Chem 112B Lab ManualSpring 2016 Chem 112B Organic Chemistry Laboratory Manual UC Riverside Spring 2016 Page | 1 Chem 112B Lab Manual CHEMISTRY 112B LABORATORY EXPERIMENTS Spring 2016 TEXTBOOKS The Organic Chem Lab Survival Manual Zubrick, 9th edition John Wiley & Sons Spring 2016 Darling Model Kits (UCR Edition) Lab Coat Student Lab Notebook: 100 Spiral *NOTE: Hold onto this book. It is used in 112C. LABORATORY INSTRUCTOR Professor Richard Hooley Chemical Sciences 1, Room 444 (951)-827-4924 email:
[email protected] ACADEMIC COORDINATOR Dr. Rena Hayashi Science Laboratories 1, Room 103 (951) 827-3143, email:
[email protected] LECTURE INSTRUCTORS Prof. Michael Marsella Chemical Sciences 1, Room 440 email:
[email protected] SPECIAL LABORATORY INFORMATION (1) It is not possible to get a passing grade for the course without completing the laboratory with a passing grade. (2) Academic dishonesty in any form will not be tolerated in this lab. In addition to the sanctions imposed on laboratory grades, all such incidents will be reported to the Office of Student Conduct for administrative review. Students found to be cheating will receive a zero grade for the experiment and may be subject to dismissal from the class with a failing grade. Cheating includes (but is not limited to) turning in a report without doing the experiment, interfering with another student's work, removing chemicals or glassware from the laboratory, or providing test questions or answers to other sections. All students enrolled in this class are also responsible for familiarizing themselves with the Student Code of Conduct. The general rules and student rights in that document apply to this lab. (3) Attendance at your assigned laboratory meetings is mandatory. If you miss a laboratory you will not be able to make-up that laboratory. For one absence only, with a verifiable medical excuse accepted by Dr. Hayashi, your laboratory score will be pro-rated. You must contact Dr. Hayashi by telephone [(951) 827-3143] immediately upon learning you will miss a lab, leave a phone number where you can be reached, and provide a medical excuse (signed by a licensed medical doctor (M.D.)) to Dr. Hayashi as soon as you return to campus. Your TA may not alter this policy. (4) Lab Preparation Write-ups (Pre-Labs) are due at the beginning of the lab period in which the experiment is to be done. (5) Laboratory Reports are due at the beginning of the lab period following completion of the experiment. (6) Enrollment questions concerning laboratory or lecture must be directed to Dr. Hayashi. (7) Note on laboratory fees: Your laboratory fee will be paying for chemicals, glassware, hotplates, and other allowable teaching items and apparatus. (8) Cellular Phones: For safety reasons cellular phones may not be operated in the laboratory. Make certain that your phone is in the off position before entering. (9) Important: Be sure to record key information about this lab, including TA name, lab room, locker number, and combination, in a place that is secure and will be accessible to you during lab. Page | 2 Chem 112B Lab Manual Spring 2016 CHEMISTRY 112 LABORATORY POLICIES on SAFETY AND PERSONAL PROTECTIVE EQUIPMENT (PPE) INSTRUCTOR Professor Richard Hooley Chemical Sciences 1, Room 444 (951)-827-4924 email:
[email protected] ACADEMIC COORDINATOR Dr. Rena Hayashi Science Laboratories 1, Room 103 (951) 827-3143, email:
[email protected] This document establishes the safety policies for students enrolled in the Organic Chemistry teaching laboratory (Chem 112LA, 112LB and 112LC) and is incorporated by reference into the course syllabus. Students failing to comply with all safety rules herein as well as any safety direction from any course staff member (TA, Academic Coordinator, or the Instructors) are subject to a variety of sanctions, including dismissal from a particular laboratory session (resulting in a zero grade for the experiment), and may be subject to dismissal from the course. Personal Protective Equipment a) Wear safety goggles at all times while in the laboratory. b) Lab coats must be worn at all time while in the laboratory. c) No exposed legs or arms are permitted in the laboratory – shorts or skirts may never be worn. d) No sandals, open-toed or perforated shoes, or shoes with absorbent soles are allowed in the laboratory. e) Nitrile gloves are supplied, and must be worn while performing all transformations. It should be noted that while gloves provide a barrier to chemicals coming into contact with skin, they do not provide perfect protection. Nitrile gloves are permeable to a number of organic liquids (especially chlorinated solvents and dimethylsulfoxide). If you spill chemicals on your gloves, remove and replace the gloves immediately. Good practices are to a) minimize spillage and other modes of contact with chemicals, and b) immediately wash your hands with soap and water after contact with any harmful reagent or solvent. General Safety a) No hats, scarves, neckties, long unrestrained hair, or overly loose clothing are permitted. b) Cellular phones may never be used in this laboratory. Make certain that your phone is turned off before entering. If you use a cellphone during lab, it will be confiscated by your TA for the duration of the lab period. c) No eating, drinking, or smoking in the laboratory. Food and drinks may never be present. This includes all visible water bottles or mugs, containers of water or flavored drinks, containers of ice intended for consumption, etc. A food or drink container may be present only if it is empty / unopened and out of sight, such as inside a backpack. d) Bicycles, skateboards, in-line skates, roller-skates, and unicycles are not allowed in the laboratory. Their use is also not allowed inside the Science Laboratories building. If skateboards are brought into the building, they may not be placed on the floor. Medical Conditions a) You should not work in the laboratory if you are pregnant or you might be pregnant. Contact course staff in this situation. In addition, notify the Academic Coordinator if you have any other medical conditions (diabetes, allergies, etc.) that may require special precautions to be taken. Page | 3 Chem 112B Lab Manual Spring 2016 Fire and Emergency a) Make sure to know the locations of safety showers, eyewash fountains, fire extinguishers, emergency telephones, fire alarms and all exits. These are clearly marked in the laboratory. b) FIRE: Immediately notify the supervising TA. A fire confined to a small flask or container can usually be extinguished by covering the flask with a large nonflammable container (e.g. beaker). Only attempt this is the fire can be easily contained: otherwise pull the fire alarm and exit the building. Go to the designated assembly area and do not use the elevator. If a person's clothing is on fire, use the safety shower to put out the flames. If this is not possible, douse the person with water, cover them with a fire resistant coat and roll the person on the floor. c) INJURY: Immediately report ANY injury to a TA, no matter how minor. The TA will initiate emergency procedures and arrange transportation to a medical facility. If you are a member of the Campus Student Health Plan, then during normal business hours go to the Campus Health Center (for current business hours go to www.campushealth.ucr.edu) After hours until 9 pm: go to Riverside Medical Clinic Urgent Care All other times: Riverside Community Hospital If you are NOT a member of the Campus Student Health Plan, then during normal business hours go to the Campus Health Center and inform them that you are not on the health plan but were injured while on campus. At all other times, obtain medical treatment through your personal health insurance coverage (i.e. HMO, PPO) d) CHEMICAL SPILL: Chemical contact with eyes and skin must be washed immediately with water for at least 15 minutes (use the eye wash/safety shower). Remove contaminated clothing and immediately report the incident to a TA. Other Laboratory Rules Do not put lab chemicals in your drawer, unless specifically instructed to do so by your TA. NO ignition sources (matches, lighters, etc) are allowed in the laboratory. There is absolutely no smoking allowed anywhere at any time in the Sciences Laboratories building. Do not pour chemicals into the sink or dispose into the trash: use the proper waste containers. Dispose of chemical waste in the specified containers - some chemicals are dangerous if mixed. Do not use unlabeled chemicals, and if you find any, report this to your TA Do not drink from lab faucets or use the ice from lab ice machines to chill food. The water may not be safe to drink. NEVER mix chemical reagents unless instructed to do so by your TA as part of your lab procedure. NEVER taste or smell chemicals. Page | 4 6: DielsAlder reaction 05/15 05/16 Exp. 1: Hydrogenation Wednesday 05/24 05/31 Check-out Reports due 05/18 05/25 06/01 05/19 05/26 06/02 05/20 05/21 05/27 05/28 06/03 06/04 Page | 5 . 04/03 04/04 04/10 04/17 04/24 05/01 04/11 Exp. 7: Electrophilic Aromatic Substitution 05/22 05/29 05/30 Academic Holiday 04/20 04/27 05/03 05/10 05/04 05/11 Thursday 03/31 04/07 04/14 04/21 04/28 05/05 05/12 Friday Saturday 04/01 04/02 04/08 04/09 04/15 04/16 04/22 04/23 04/29 04/30 05/06 05/07 05/13 05/14 05/17 05/23 Exp. 3: NMR analysis of bromoindanol 04/19 04/25 Exp.Chem 112B Lab Manual Sunday Spring 2016 Monday Tuesday 03/28 03/29 Lab Safety & Check-in. 5: Chemoselective Epoxidation 03/30 04/05 Exp.4: Alcohol Oxidation 04/26 05/08 Exp. 8: Synthesis of a Cyclic Acetal 04/13 05/09 04/06 04/12 05/02 Exp. 2: Hydroboration 04/18 Exp. Read Safety Handout. 04/25-04/29 Experiment 4: Oxidation of a Secondary Alcohol . Mon. 04/04-04/08 Experiment 1: Catalytic Transfer Hydrogenation of an Olefin (30 pts).Chem 112B (Spring 2016) For each experiment. Read Klein 2nd Ed pp 435-439 (olefin hydroxybromination). 77-83 (clean and dry).Synthesis of a Cyclic Acetal (30 pts). Read Klein 2nd Ed section 20. Lab Handout p 29-30. p 20-22. 77-79 (clean and dry). Read Klein 2nd Ed pp 648-651 (alkene epoxidation). 269-303 (IR spectroscopy). (30 pts). Lab Handout p 12-14. Read Klein 2nd Ed pp 428-431 (olefin hydrogenation). Page | 6 . 141-144 (liquid-liquid extraction). Klein 2nd Ed pp 422-428 (olefin hydroboration). 1195-1197 (Amino Acids).5. 889-893 (Electrophilic Aromatic Substitution). Read Klein 2nd Ed pp 876-879. 8 lab reports) 05/31-06/03 Check-Out --. pp 1-37. You MUST make sure that you have all of the necessary lab equipment and glassware in your assigned drawer before you leave. Experiment-specific reading is stated below. Lab Handout p 18-19. Read Klein 2nd Ed pp 609-612 (alcohol oxidation). Lab Handout p 26-28. These can be found in Zubrick: pp 1-37. 798-803 (Diels-Alder Reaction). Laboratory is worth a total of 240 points. 04/18-04/22 Experiment 3: Hydroxybromination of Indene . Read Zubrick. pp 939-947 (acetal formation). May 30 Academic Holiday (*Monday sections arrange time with TA to turn in Expt.Synthesis of Camphor. 04/11-04/15 Experiment 2: Hydroboration of Indene . 8 Reports due. 195-199 (rotary evaporator). pp 1079-1083 (conjugate addition). you should be familiar with the standard techniques taught in Chem 112A.Chem 112B Lab Manual Spring 2016 Schedule of Experiments . 684-706 (IR spectroscopy). Lab Handout p 9-11. Lab Handout. Lab Handout p 23-25. 05/23-05/27 Experiment 8: Protecting Groups . 222-233 (thin layer chromatography). 05/02-05/06 Experiment 5: Chemoselective Epoxidation of a Natural Terpene (30 pts). Read Klein 2nd Ed pp 684-706 (IR spectroscopy). 87-92 (melting point).Structural Analysis by NMR (30 pts).Exp. Lab Handout p 15-17.NMR Determination of Regioselectivity (30 pts). 05/09-05/13 Experiment 6: Dueling Pericyclics: Cheletropic Cycloreversion and Diels-Alder Cycloaddition (30 pts). Dates Experiment 03/28-04/01 Laboratory Safety & Check-in. (30 pts). pp 120-126 (recrystallization). Lab Manual Special Section (p31-44). Lab Manual Special Section (p31-44). Lab Manual Special Section (p31-44). 732766 (1H NMR spectroscopy). 767-768 (13C NMR spectroscopy). 05/16-05/20 Experiment 7: Synthesis of a Thyroid Hormone Precursor Analog via Electrophilic Aromatic Substitution. which you will test by experiment. Some guidelines are given below: a) The laboratory notebook must not be loose leaf. A copy of your notebook pages containing observations noted during the lab experiment. This can be written on separate loose-leaf paper. This is due at the start of each experiment. Part III . NO red ink!) c) Other textbooks.Prelab Report. g) Prelab question answers. f) Outline of procedure. It is your responsibility to propose what you expect to determine from each experiment. PRELAB REPORT (10 pts) The initial part of your lab report must be written in your laboratory notebook. Make sure you note any necessary safety precautions. I. e) List of equipment (sketch complex apparatus). A copy of your lab notebook pages containing the lab writeup and answers to any prelab questions. iPads or cellphones are not allowed in the laboratory. d) List of chemicals: masses or volumes. b) The title and number of the experiment. Lab notebooks are available from the campus bookstore and are designed so that they permanently contain the original pages of your Prelab and Postlab reports. e) Your TA may periodically inspect your notebook.Results. A summary of results and answers to postlab questions. loose sheets of paper. Look up molecular masses and calculate the material amount in moles (if appropriate). c) Objectives. d) Copies of your lab notebook pages are required for grading. Page | 7 . lab manuals. lab section and the name of your TA (on each page). The assigned notebooks are designed so that the carbon copies can be removed and handed in to your TA. b) Use permanent blue or black ink only (ballpoint pen. The complete outline of procedures must be written in your laboratory notebook prior to performing the experiment. This must be sufficiently detailed to allow you to perform the experiment. Part II .Chem 112B Lab Manual Spring 2016 FORMAT FOR LABORATORY NOTEBOOK REPORTS Keeping an accurate laboratory notebook is essential to your success in this class. It will consist of: a) Your name. These will always require an analysis of the hazards and risks associated with the experiment. YOUR LAB REPORT CONSISTS OF THREE (3) PARTS (30 pts) Part I . The carbon copy pages of this report must be handed in BEFORE you begin the experiment. This should include hypotheses about the outcome of the lab. boiling/melting points (bp/mp) and density (if appropriate).Postlab Report. A copy of the original pages of this report will be collected prior to the experiment and will be returned to you after the whole lab is graded. Describe problems that may have occurred and possible solutions. etc) recorded during the lab session. and consists of: a) Your name. d) Characterization materials: include copies of spectra. lab section and the name of your TA (on each page). Page | 8 . lab section and the name of your TA (on each page). Staple Parts II and III together and turn into your TA at the beginning of the next week's lab session. b) The title and number of the experiment. c) Analysis of results: In 5-10 sentences.it can be written on separate loose leaf sheets and stapled to your results copy pages.Chem 112B Lab Manual Spring 2016 II. A combined copy of the Results/Postlab report will be stapled and turned in to your TA after the experiment is complete. comment on the outcome of your experiment. You should keep a copy of Part III for yourself. III. RESULTS (3 pts) This section should be started on a fresh page of your notebook. measured mp/bp of your products and any other observations (color changes. Turn in your product(s) from the experiment in a suitably labeled vial to your TA at the end of the lab session. How and why did the outcome differ from that predicted in your prelab report? What was learned from the experiment? d) Answers to postlab questions. after the prelab report. notably the quality of your results. POSTLAB REPORT (17 pts) This section does not need to be written in your lab notebook . measured masses and volumes used in the experiment (if you use different amounts from the procedure. c) Results: Date. This section should be completed during the lab session and consists of: a) Your name. note this). times. It is to be completed after the lab period at home. b) The title and number of the experiment. etc. recorded during the lab session.. add the ethanol only after swirling the reagents together in the flask. In industry. hydrogen gas is used with a metal catalyst at high pressure and temperature. Make sure you correctly calculate the molar amounts of your reactive materials. so you will use a hydrogen "surrogate" .-eq.00 Ammonium formate 10% Palladium on carbon Ethanol amount 472 mg -- --- -- -- 42 mg -- 16 mL product 3) Based on your answers to Q2. A hydrogenation that uses something other than molecular hydrogen is called a transfer hydrogenation.virtually all synthetic menthol (mint flavoring) requires a catalyzed alkene hydrogenation for manufacture. 2) Fill in the reaction table below. assuming 100% conversion to product. the mass you would expect to recover. but only one of them is reactive towards hydrogen (you'll learn why this is later in the course). There are a number of double bonds in ethyl cinnamate.ammonium formate. i. you will perform a selective alkene hydrogenation. and then add 16 mL ethanol to the flask. This method is unsuitable for a teaching lab. Experiment 1. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product. 684-706 (IR spectroscopy). not Page | 9 . 472 mg ammonium formate. (NOTE . Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a).e. MW mmol 168 μL 1. Hydrogenation is a vital reaction in the chemical industry . NOTE . Reaction Setup To a 50 mL round bottom flask equipped with a magnetic spin bar add 168 μL ethyl cinnamate. name formula Ethyl Cinnamate mol. and analyze the reaction with IR spectroscopy and thin layer chromatography. Swirl the flask to mix the contents. Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn.Catalytic Transfer Hydrogenation of an Olefin Reading: Klein 2nd Ed pp 428-431 (olefin hydrogenation). Transfer the flask to a sand bath on a magnetic stirrer. You will reduce ethyl cinnamate using a transfer hydrogenation process. and the safety precautions you will take when handling this material. Introduction In this experiment.clamp the flask joint.Chem 112B Lab Manual Spring 2016 Experiment 1 . and 42 mg palladium on carbon (10 wt%). analyze the product by running TLC with two lanes: one lane for starting material and another one for the product. Extract the aqueous layer with an additional 5 mL of ether and combine the two ether solutions. Evaporate the ether in vacuo. Characterization Weigh the product and calculate the percent yield. draw the next two most favorable resonance structures (ignore resonance with the aromatic ring).Chem 112B Lab Manual Spring 2016 the condenser!). b) For your hydrogenation product. On a silica gel TLC plate. Rinse the flask with 5 mL of ether and transfer this rinse to the separatory funnel. Transfer the ether solution into a clean flask and dry it with anhydrous sodium sulfate for 15 min. Rinse the reaction flask with 2 mL of ethanol and pass it though the filter pipette into the flask containing the product solution.5 mL of ether. Remove the solvent from the product solution via rotary evaporation. Filter the dried ether solution through a cotton-clogged funnel and collect the filtrate in a clean. Pour the ether layer (containing your product!) into another labeled flask. The palladium catalyst must be kept wet. Page | 10 . Figure 1. draw one more favorable resonance structure. rinse the pipette with 3 mL of water into a small beaker. as it is an ignition risk. 2. Wash the ether solution with 5 mL of water and drain the aqueous layer. then remove the flask and cool in an ice bath for 5 min. 3. Isolation of product After heating. dry. NOTE . weighed 50 mL round bottom flask. Post Lab Questions (1) Identify the peak(s) in the IR spectra of ethyl cinnamate and your hydrogenation product that correspond to the C=O stretch in each molecule. Drain the aqueous layer into a labeled flask. Attach a water-cooled reflux condenser to the flask and heat the reaction mixture at 60°C for 1h. spot the product dissolved in ether. Prepare the reference TLC solution by dissolving 1 drop of ethyl cinnamate in 0. While waiting for ether solution to dry. Dip the TLC plate in permanganate stain to visualize. Develop the TLC plate in Ethyl acetate:Hexane = 30:70. Schematic of the reaction apparatus. Transfer the cooled reaction mixture into the filter pipette (via pipette) and collect the filtration in a 100 mL round bottom flask. Add 5 mL of water and 20 mL of ether to the crude product in the flask and transfer the mixture to a separatory funnel. (2) These are the most important resonance structures for ethyl cinnamate and the product: a) For ethyl cinnamate.immediately after you have collected your product from the filter pipette. Prepare a filter pipette packed with approximately 1 cm of Celite. raise the reaction from the sandbath and let cool. Take an IR spectrum of the product. (5) Draw the product of the hydrogenation of the deuterated equivalent of trans-ethyl cinnamate shown below. indicating all stereochemistry. explain why the frequency of the C=O stretch in the hydrogenation product is higher than in ethyl cinnamate. would you expect any difference in product? Explain your answer. (8) Why does the starting material react with KMnO4 stain and not the product (read Klein p444)? Page | 11 . (7) Explain why there is little difference between the Rf values for starting material and product in the TLC analysis. (6) If you performed the reaction from Q5 on the deuterated version of cis-ethyl cinnamate rather than trans-ethyl cinnamate.Chem 112B Lab Manual Spring 2016 (3) What single factor mainly determines the stretching frequency in IR spectroscopy? (4) Based on your answers to Q1-3. 00 Borane:THF (1M) amount 0. the most important technique for structure determination is NMR Spectroscopy. and can distinguish them based on their chemical environment.-eq. the mass you would expect to recover. Always close the borane-containing flask tightly once you have collected your sample. name formula Indene mol. assuming 100% conversion to product.NMR Determination of Regioselectivity Reading: Klein 2nd Ed pp 422-428 (olefin hydroboration).8 mL 30% hydrogen peroxide -- -- -- -- 1 mL 3M NaOH solution -- -- -- -- 0. MW mmol 1. you will perform a selective hydroboration/oxidation reaction of indene. Introduction So far. In this experiment. To a 10 Page | 12 . 767-768 (13C NMR spectroscopy).e. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product. hydrogen atoms) and 13C (i. Lab Manual Special Section (p31-44).5 mL -- 2. Reaction Setup NOTE: make sure your glassware is DRY for this experiment: the borane is water-sensitive. Experiment 1. NMR spectroscopy detects different atomic nuclei in the molecule. 2) Fill in the reaction table below. While melting points. Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. and use 13C NMR to determine the structure of your product. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a). i.Chem 112B Lab Manual Spring 2016 Experiment 2: Hydroboration of Indene . IR spectra and mass spectra are useful. carbon atoms). and the safety precautions you will take when handling this material. The two most common (and useful) nuclei detected by NMR are 1H (i. Make sure you correctly calculate the molar amounts of your reactive materials.e.e.7 mL product 3) Based on your answers to Q2. you have used a limited number of methods to determine the structure of the products you synthesize in lab. Purification by Recrystallization The crude product is contaminated with a polymer which is insoluble in hot hexanes. If the product does not crystallize.5 mL of indene. 2. how many peaks would you expect to see in the 13C NMR spectra of the following molecules? Page | 13 . Can it distinguish between the two products of the reaction? Explain your answer. which contains your product. broadness. Characterization Weigh your purified product to determine the yield. and place in a clean flask. Your TA will give you a 13C NMR spectrum of your product. Dissolve your product in a minimum amount of hot hexanes. Your product should solidify. strength) of the new peak in the product spectrum. with one big difference. isolate the product by vacuum filtration. 3. Your product will not crystallize if this is present. Compare your observed melting point to the literature value. Remove the reaction flask from the ice-water bath and heat the flask with stirring at 50 ºC for 30 min. 4. Extract the aqueous layer with ether (3 x 4 mL) and be sure to combine all your organic layers. After the addition of water is complete. Hand this in with your postlab report. Describe the nature (frequency. They will be rather similar. With that in mind. Make sure to leave behind the oily polymer. Place the reaction flask in an ice-water bath to cool. Pipette out the hexanes solution. Place the flask that contains your product dissolved in hexanes on the rotary evaporator and remove the solvent. Post Lab Questions (1) Write the mechanism for the two steps of the hydroboration/oxidation reaction of indene. and explain what functional group this new peak denotes. only one peak is seen in the spectrum. (2) Compare the IR spectra of your purified product and the indene starting material. Filter off the Na2SO4 and remove the solvent by rotary evaporation.Chem 112B Lab Manual Spring 2016 mL round bottom equipped with a magnetic spin bar add 0. Wash the combined organic layers with brine (~5 mL) and dry with Na2SO4 for 10 mins. (4) The key concept in 13C NMR spectroscopy is symmetry . Isolation of Product After 30 min of stirring. Take an IR spectrum of both your purified product as well as the indene starting material.if two carbon atoms are related by symmetry. add 0. and determine the melting point of your purified product. add BH3•THF dropwise (with stirring) at 0 ºC. Pour the two-phased mixture into a separatory funnel and remove the organic layer. Once cooled. Let stir for 20 min at room temp before cooling in an ice-water bath and adding water DROPWISE (~1 mL) with stirring while keeping the solution cool. remove the flask from the hot plate and let the reaction mixture cool to room temperature (~5 min) and then add ether (~1 mL). scratch the bottom of the flask with a glass pipette to aid the crystallization process. If crystals still do not form then recrystallize from hot hexanes by dissolving in a minimal amount of hot hexanes and allow to cool to room temperature slowly. (3) IR can tell the presence or absence of functional groups in a molecule. Once recrystallization is complete.7 mL of 3M NaOH followed by 1 mL of 30% H2O2. Explain the observed regioselectivity of the reaction. Which isomer was formed? Explain your answer with respect to the NMR data. why do you get the isomer from Q6? Page | 14 . i. How many peaks are present in the aromatic region of the 13C spectrum? How many peaks are present in the aliphatic/sp3 region of the spectrum? (6) Based on your answers to Q4/5. determine the structure of your product. (7) Go back to the mechanism of reaction you wrote in Q1.Chem 112B Lab Manual Spring 2016 (5) You were provided with a 13C NMR spectrum of your product. in chemical terms.e. 732-766 (1H NMR spectroscopy). The reaction here is very short.36 g of Page | 15 .36g 1:1 CH3CN:water -- -- -- -- 10 mL product 3) Based on your answers to Q2. p732-766 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Introduction In this experiment.00 Ammonium bromide 215 mg OxoneTM.Chem 112B Lab Manual Spring 2016 Experiment 3: Hydroxybromination of Indene . i. notably to determine coupling constants and to discuss more complex coupling patterns than the simple examples you use in lecture. assuming 100% conversion to product.-eq. and the safety precautions you will take when handling this material. You will use 1H NMR in your analysis of this experiment.Structural Analysis by NMR Reading: Klein 2nd Ed pp 435-439 (olefin hydroxybromination). You will use the end of the lab period to analyze the MS and NMR spectra of your product. MW mmol amount 233 μL 1. the mass you would expect to recover. To this solution add 215 mg of ammonium bromide and 1. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product. Reaction Setup In a 50 mL round bottom flask equipped with a magnetic spin bar added 233 μL of indene and 10 mL of a 1:1 mixture of acetonitrile and water. but this time you will perform a hydroxybromination reaction. Experiment 1. Prelab Questions . The outcome of this reaction is more complicated than in Expt 2. Make sure you correctly calculate the molar amounts of your reactive materials. KHSO5 1. 2) Fill in the reaction table below. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a). and you will perform a more detailed NMR analysis to confirm the product structure. in consultation with your TA. you will again use indene as your alkene starting material.e. Lab Manual Special Section (p31-44).Read Klein. name formula Indene mol. (4) There is a cluster of peaks in the 1H NMR spectrum between δ 7-8 ppm. Filter off the white solid by vacuum filtration and allow to dry under vacuum (~5-10 min). Dissolve your product in a minimal amount of hot ethanol (~1 mL should be sufficient) and allow to cool slowly to room temperature.5 ppm labeled 1 . Which hydrogen atoms in your product do those peaks correspond to. 37).Chem 112B Lab Manual Spring 2016 oxone. Your TA will provide you with a 1H NMR and Mass spectrum of your bromoindanol product. Add another 5 mL of water to aid in precipitating out all of your product. Purify your product by recrystallization. and that of the indene starting material. you do not need to hand in a discrete "analysis" section (i. Post Lab Questions. to a very faint yellow. 4. and describe two pieces of information that the mass spectrum provides that confirm the identity of the product. At this point you should see some solid present in your flask.c. triplet. How many chemically inequivalent hydrogen atoms are left in this molecule? Explain how you determined your answer. How can these spectra help you determine whether the reaction worked? (3) Can the IR spectra help with determining the regioselectivity of the reaction (i. Compare your observed melting point to the literature value. (2) Describe the difference between the IR spectrum of your product. Page | 16 .e. Identify the M+ peak. Now.e. page 8). and why? (5) Read p43 of this handout. The postlab questions will help you perform this analysis and will comprise the entirety of your part III grade. IR/MS Analysis (1) Look at the mass spectrum of the product. p31-44 For this experiment. to yellow. Read the "Special Section". doublet. (Ammonium bromide is hygroscopic. Collect your product by vacuum filtration. Purification by Recrystallization At this point your product is mostly pure but contains some slight impurities.e. Note . III. (7) a) Describe the coupling pattern (i.31. and identify the peak in the 1H NMR spectrum corresponding to the OH hydrogen in the product. 3. (6) You have now assigned five of the protons in the molecule. Isolation of Product After 2 minutes. you will identify which product isomer you formed by analyzing the 1H NMR spectrum in stages. 2. Be sure to cap the reagent bottle when you have finished weighing out what you need!) Let the reaction stir for 2 minutes at room temperature.the 1H NMR spectrum was obtained on a 300 MHz spectrometer. which isomer is formed)? Why/why not? NMR Analysis Here. filter off the precipitate by vacuum filtration. doublet of doublets etc) for the peak at δ 5. Pour your filtrate into a round bottom flask and remove the acetonitrile by rotary evaporation. the acetonitrile should be gone. Obtain an IR spectrum of the product and the indene starting material. This is your product which is insoluble in water. and calculate the coupling constant (J) value(s) (see p34. You will not be able to remove the water on the rotovap so when the volume has decreased to about half. Characterization Weigh your purified product to determine the yield and obtain a melting point. You will see the reaction mixture change color from orange.4 in the 1H NMR spectrum. consider the peaks from δ 3-5. and why that product is the one you characterized. While the experimental procedure is more tedious than the method you used.Chem 112B Lab Manual Spring 2016 b) Describe the coupling pattern (i. (10) An O atom is more electronegative than a Br atom. is X OH or Br).60. (11) Another (less effective) way to perform this reaction is to use hypobromous acid (Br-OH) as reagent. (9) I have labeled the 4 protons in the product Ha . (8) Using the coupling constants you calculated in Q7.e. which of the numbered peaks 1-4 correspond to protons HAD?). d) Describe the coupling pattern (i.e. doublet of doublets etc) for the peak at δ 4. doublet.29. and thus which isomer of bromoindanol you formed. c) Describe the coupling pattern (i. doublet. and calculate the coupling constant (J) value(s). Explain why you chose that stereochemical outcome of the reaction. Look at the relative chemical shift of peaks 1-4 and identify the nature of X and Y in your product (i. draw the actual product obtained. does 1 couple with 2.e. Page | 17 . identify which protons 1 . (12) We have been focused on regiochemistry so far. and calculate the coupling constant (J) value(s). doublet of doublets etc) for the peak at δ 3. Based on the mechanism you drew in Q11 (and having read Klein p438). Write an arrow pushing mechanism for the reaction below. etc). triplet. and calculate the coupling constant (J) value(s). and explain why a single product is formed.Hd below.e. Use your answer to Q8 to help.e. Ignoring the identity of X and Y (we'll get to that later) assign the 1H NMR spectrum (i. with the correct relative stereochemistry assigned.e.4 couple to each other (i. doublet of doublets etc) for the peak at δ 3.25. triplet. doublet. triplet. the mechanism is easier to write. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product.glacial acetic acid is corrosive and toxic .15% aqueous solution) -- -- -- 3. Prelab Questions Figure 1. you will oxidize a secondary alcohol (isoborneol) to the corresponding ketone. 2) Fill in the reaction table below.e. but it is now known that Cr(VI) salts are not only heavy metal pollutants. Note . It is generally preferable in modern organic chemistry to use reagents and solvents that have minimal environmental impact.-eq.0 mL Glacial Acetic Acid -- -- -- 0. dichromate salts were used in oxidation reactions. assuming 100% conversion to product. Reaction Scheme. MW mmol amount Isoborneol 1. Remove the ice bath following the addition. Make sure you correctly calculate the molar amounts of your reactive materials. i.0 mL of Clorox. but will still perform the reactions we wish to achieve. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a).all manipulations should be performed in the fumehood. Page | 18 . name formula mol.Chem 112B Lab Manual Spring 2016 Experiment 4: Oxidation of a Secondary Alcohol . but is much more rapidly broken down. Dispense the glacial acetic acid in the hood by means of an automatic delivery pipette.9 mL product 3) Based on your answers to Q2. Cool the resulting solution in an ice bath and add dropwise. This is an example of a (relatively) “green” experiment. but also carcinogens. the mass you would expect to recover. Add the Clorox by inserting the pipette down the neck of the reflux condenser just into the throat of the round bottom flask. 3.Synthesis of Camphor Reading: Klein 2nd Ed pp 609-612 (alcohol oxidation) Introduction Primary and secondary alcohols can be oxidized to form a number of carbonyl compounds. Add 900 μL of glacial acetic acid and then attach the flask to an air-cooled reflux condenser. Instead we will use hypochlorite (household bleach) – this compound still has an environmental impact to be sure. 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. with stirring.00 300 mg NaOCl (6. In this experiment. camphor. and the safety precautions you will take when handling this material. Experiment 1. Historically. Reaction Setup Weigh and place 300 mg of isoborneol in a 10 mL round bottom flask containing a magnetic spinbar. 4. Characterization Weigh the product and calculate the percent yield. Stop stirring the mixture and allow the layers to separate. Pour the mixture over 6 mL of brine (saturated NaCl) and ice [take 6 mL brine and add a little bit of ice]. using HOCl as reagent. 3. Post Lab Questions (1) Describe the difference between the IR spectrum of your ketone product. Isolation of Product Using a Pasteur pipette. Vacuum filter the precipitate and wash with cold water. Use of bleach is a more "green" process. however. Purification by Recrystallization Dissolve the crude product into a small amount (LESS THAN 1 mL) of boiling 2:1 Ethanol:H2O solution. cool it to room temperature then keep it in an ice bath for 5 min. When all the crude is dissolved. Remove a few drops of the aqueous layer with a pipette and drop them on a small piece of dampened starch/iodide test paper. Determine the melting point and obtain an IR spectrum of the product. 2. Draw the arrow pushing mechanism of your reaction. How can these spectra help you determine whether the reaction worked? (2) The 1H NMR spectrum of camphor is complex. so we won't use that for characterization. A positive KI-starch test should be obtained at this point (white KI-starch paper will turn blue-violet for positive test). collect the solid by vacuum filtration using a Hirsch funnel. (6) A more usual technique for this reaction is to use chromic acid (HCrO4). Instead. add a saturated aqueous sodium bisulfite solution dropwise to the reaction mixture until the solution gives a negative KI-starch test (white paper stays white). Air-dry the solid and weigh the crude product. Dry the resulting solid on the filter. (7) Why did you add sodium bisulfite at the end of the reaction? Page | 19 .Chem 112B Lab Manual Spring 2016 Stir the resulting solution at room temperature for 30 min. which is the active ingredient in this reaction. and that of the alcohol starting material. How many chemically different hydrogen atoms are present in camphor? (5) The combination of sodium chlorite and acetic acid forms hypochlorous acid (HOCl). Explain why the method you used is more environmentally friendly than use of chromic acid. consider the structures of starting material and product and describe how 13C NMR analysis could determine whether your oxidation was successful. (3) How many stereocenters are there in isoborneol? How many are there in camphor? (4) Q3 explains why the 1H NMR spectra are complex. and wash it with saturated sodium bicarbonate solution until CO2 gas is no longer evident. This test is intended to indicate whether insufficient or excess bleach was added to the solution: the indicator paper will turn black in the presence of bleach. 5 mL methanol -- -- -- 8 mL product 3) Calculate the Theoretical Yield of your product. employing spectroscopic and mechanistic analysis. the mass you would expect to recover (assuming 100% conversion to product). Introduction Synthesis of more complex targets often requires the selective reaction of one functional group in the presence of another similar group.Chemoselective Epoxidation of a Natural Terpene Reading: Klein 2nd Ed pp 648-651 (alkene epoxidation). you can selectively epoxidize either of those alkene groups. you will perform a chemoselective epoxidation reaction on the natural terpene (D)-(+)carvone (an essential oil isolated from caraway seeds). 2) Fill in the reaction table below.0 0. B and C is quite challenging by IR spectroscopy alone . name formula mol. Make sure you correctly calculate the molar amounts of your reactive materials. MW mmol amount (D)-(+)-carvone 1. In this lab. (D)-(+)-Carvone has two different alkene groups: by varying the reaction conditions.-eq. Understanding the mechanism of the reaction is vital for predicting whether a reaction can be chemoselective. 4) Distinguishing between the products A. Possible epoxidation products of (D)-(+)-Carvone. a process called chemoselectivity. Some reactions are incapable of good chemoselectivity. pp 1079-1083 (conjugate addition).72 g 6M Aqueous NaOH -- -- -- 1 mL 30% Aqueous H2O2 -- -- -- 1.e. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a). You will perform a base catalyzed epoxidation using hydrogen peroxide and determine which double bond reacts. Which functional groups are the same. Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. and which are different? Page | 20 . and the safety precautions you will take when handling this material.explain the differences and similarities that you would expect to see in the corresponding IR spectra.Chem 112B Lab Manual Spring 2016 Experiment 5 . i. as they do not sufficiently differentiate between the two reactive groups. Figure 1. 0. TLC Analysis of your product Dissolve a small amount of the crude product (a few mg will be enough) in 3-5 mL of dichloromethane. Page | 21 . Your TA will give you partial 1H NMR spectra of your starting material and product. Separate the layers. Hand these in with your postlab report. showing the double bond regions. Which of the two possible ionic species is more reactive towards electrophiles? Note . Dry the organic extract with sodium sulfate. Wash the flask with another 5 mL of ether and 10 mL brine.72 g) and methanol (8 mL) in a 50 mL round bottom flask containing a stir bar. Spectroscopic Analysis of your product Weigh your purified product and determine the yield. 2. Hb and Hc.Chem 112B Lab Manual Spring 2016 5) Draw the mechanism of reaction of H2O2 with NaOH. Obtain an IR spectrum of your product. Develop the TLC plate in a TLC chamber using hexane/ethyl acetate (10:1) as the eluent.0 ppm). Cool the mixture to 0°C in an ice bath and add 1. and transfer to a separatory funnel. 4. Based on chemical shift or coupling considerations. NaOH solution dropwise over a period of 1-2 minutes.remember this question when you answer postlab question 1… Experiment 1. There are three peaks in this region in the carvone spectrum. the reaction of an alkene with H2O2 and base. assign the peaks for Ha and Hb/c (you can't distinguish between Hb and Hc. making sure you stir the solution well. Add 1 mL of 6N aq. use methyl vinyl ketone as your alkene: (2) The other method of epoxidation is the use of a peracid.7. transferring the organic (upper) layer to an Erlenmeyer flask. Spot (D)-(+)-carvone onto the TLC plate for comparison as well.e. Analyze the composition of the product mixture. and add the organic layer to your Erlenmeyer flask containing the other ether layer.5 mL of 30% H2O2 dropwise. Remove the TLC plate from the chamber and allow the solvent to evaporate completely. Isolation of Product Add 10 mL of ether to the flask. Stir the mixture at 0°C for 15 minutes and then at room temperature for 20 minutes. remove the solid by gravity filtration. Extract the aqueous layer with another 10 mL of ether.75 mL. Apply a small amount of the sample solution to a piece of TLC plate with a capillary. and remove the ether by rotary evaporation.0 . Post Lab Questions (1) Draw the mechanism of the reaction you performed. 3. using a pipette. so just label both peaks Hb/c). Visualize the TLC plate by immersing it briefly into a 3% ethanolic solution of phosphomolybdic acid and then heat it with a hot-air gun. and returning the aqueous layer to the separatory funnel. Reaction Setup Combine (D)-(+)-Carvone (0. and add those solutions to the separatory funnel. corresponding to Ha. For simplicity. Draw the mechanism of this reaction. i. so we've only given you partial spectra (from δ 3. using cyclohexene as your alkene: (3) The 1H NMR spectra of carvone and the epoxidation product(s) are extremely complicated. like meta-chloroperbenzoic acid (m-CPBA). i. which alkene was epoxidized and which alkene (if any) was not? (5) Explain why the reaction with H2O2 gives this specific product. B or C) would you expect to obtain? Explain why. A or B? Explain why. You may want to refer to Expt 1. (7) While IR spectroscopy isn't the best method for analysis here. (6) If you reacted (D)-(+)-carvone with m-CPBA. Is the product A.e. higher frequency) C=O stretch. based on your mechanistic analysis from Q1 and Q2. based on your mechanistic analysis from Q1 and Q2.e. Which of the products will have a stronger (i. determine the structure of the product. what product (A.Chem 112B Lab Manual Spring 2016 (4) Based on your answer to Q3 and the partial 1H NMR spectrum of your epoxidation product. Q2-4… Page | 22 . it can be used to distinguish the products. B or C. Chem 112B Lab Manual Spring 2016 Experiment 6: Dueling Pericyclics: Cheletropic Cycloreversion and Diels-Alder Cycloaddition Reading: Klein 2nd Ed pp 684-706 (IR spectroscopy). you will perform a combination of a Diels-Alder cycloaddition and a "cheletropic cycloreversion". In this experiment. 2) Fill in the reaction table below. Discovery of this novel type of reactivity led to a Nobel Prize for Otto Diels and Kurt Alder in 1950. a reaction that involves neither a nucleophile or an electrophile. Introduction The Diels-Alder reaction is the most famous example of a a pericyclic reaction.3 diene and an olefin (called the dienophile. it can form 1. and the safety precautions you will take when handling this material.25 g Maleic anhydride 1. pericyclic reactions are reversible. Experiment Before starting this experiment.3-butadiene upon heating by expelling gas molecule. the mass you would expect to recover. Since then. As you are aware from class. preheat a sand bath to 140°C.5 mL Toluene - - - 7 mL - - - ~1 mL Petroleum ether (ligroin) - 750 mg Product 3) Based on your answers to Q2.-eq Mw mmol 3-sulfolene amount 1. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product.e.e. The compound sulfolene is a diene surrogate. name formula mol. i. because it likes dienes). This reaction is controlled by favorable overlap of π orbitals between a conjugated 1. You will perform the combination process and analysis the two mechanisms present in the reaction. so the cycloreversion reaction merely means that we will perform the reverse of a cycloaddition. i. A cheletropic reaction is a subclass of the Diels-Alder reaction whereby both new bonds are made to the same atom.00 Xylenes - - - 0. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a). 798-803 (Diels-Alder Reaction).e. Make sure you correctly calculate the molar amounts of your reactive materials. assuming 100% conversion to product. i. Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. as sufficient heating is crucial. Page | 23 . a vast number of different types of pericyclic reactions have been discovered (as you will discover in Chem 112C). Ensure your temperature is high enough before running the reaction. Remove the Hirsch funnel and pour the solution into a 50 mL Erlenmeyer flask.the second is the easiest.25 g). the tip of a spatula. Bring this mixture to a boil and filter it hot (quickly!) through a Hirsch funnel into a 25mL filter flask. spot each of the solutions above onto the corresponding position on the TLC plate. Draw the structure of SO2 including lone pairs (if any).Chem 112B Lab Manual Spring 2016 1. bearing in mind the structure of SO2 and the fact that this is essentially a reverse Diels-Alder. and why is has that particular stereochemistry. 2. Post Lab Questions. 3. Attach a water-cooled condenser and transfer the flask to your sand bath. or glass pipette for liquids) of your starting material (maleic anhydride) and recrystallized product to the appropriately labeled test tube. additional hot toluene can be used to redissolve it. Sulfolene decomposes to a gas molecule and 1. Reheat the filtrate in the flask until all particulates redissolve.3-butadiene. and 0. as well as an IR spectrum of maleic anhydride. and set aside in a test tube for TLC analysis later. (1) The mechanism has two steps . then use hexane:ethyl acetate (1:1) as the eluent to develop the TLC plate and visualize using KMnO4 stain. (2) That leaves the question of how sulfolene decomposes to 1. Allow the ethyl acetate to evaporate. maleic anhydride (750 mg). Explain why one product is formed. so we'll do that first. First. Collect the crystalline solid by vacuum filtration using your Hirsch funnel and side-arm flask. Note: If product crystallizes in the filter funnel. Add petroleum ether dropwise to the hot solution while swirling until the mixture appears cloudy. Characterization Weigh the product and determine a yield for your reaction. Heat the solution again until clear and then cool on an ice bath to crystallize your product. Begin cooling the condenser immediately. consider the SO2 molecule (think back to Chem 1). add 3-sulfolene (1. Transfer the reaction to a larger flask and add 7mL of toluene and 500mg of powdered activated carbon. draw a baseline and mark 2 positions for the maleic anhydride and Product. Draw two resonance structures of SO2. Diels-Alder Reaction Into a 10 mL round bottom flask containing a magnetic spinbar. Analysis by TLC: Set up two clean. Carefully remove 1 small drop from the reaction mixture using a glass pipette. dry test tubes and label them as Maleic Anhydride and Product. (3) Now. Obtain a melting point and IR spectrum of your purified product. Using a micropipette. Isolation and purification of product Remove the flask from the hot plate and let the reaction mixture cool for about 5 minutes. On a silica TLC plate. Add 0.5 mL ethyl acetate and shake to dissolve. The butadiene formed can then react with maleic anhydride. (4) Only one (cis) isomer of product is formed in the Diels-Alder cycloaddition. Draw the mechanism of this Diels-Alder cycloaddition.5 mL xylenes. making sure to observe a steady reflux (~1 drop every few seconds). Dry the precipitate on the filter. Heat the reaction for 30 minutes.3-butadiene and SO2. draw the mechanism of the cycloreversion reaction.g. Transfer a small amount (e. Page | 24 . determine the frequency of the C=O stretch in maleic anhydride and your product. and looking back to Expt 1 postlab questions 1-4. (6) This does not hold for other dienes. Draw the exo and endo products of the reaction of cyclohexadiene with maleic anhydride. and explain why the distinction is irrelevant here. (7) From your two IR spectra. Draw the "endo" and "exo" products of your Diels-Alder reaction. How can these spectra help you determine whether the reaction worked? Page | 25 . explain the difference in C=O stretching frequencies between maleic anhydride and your product. Make sure you label your answers properly as endo or exo. Which molecule has a higher C=O stretching frequency? What single factor mainly determines the stretching frequency in IR spectroscopy? (8) Based on your answer to Q7.Chem 112B Lab Manual Spring 2016 (5) One of the benefits of using butadiene as diene is that you don’t have to worry about assigning endo vs exo. 00 0. Unfortunately. 2) Fill in the reaction table below. the difference in structure between T3 and T4 is the number of iodine atoms attached to the aromatic rings. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product. assuming 100% conversion to product. whereby we will brominate a substituted phenol with copper (II) bromide. name formula mol. analyze the regioselectivity of your reaction by 1H NMR spectroscopy and compare the NMR spectrum with that of natural iodotyrosine. In this experiment.10g Acetonitrile - - - - 3mL Product 3) Based on your answers to Q2.-eq Mw mmol amount 4-tert-butylphenol 1.00 1.250g Copper (II) Bromide 3.Chem 112B Lab Manual Spring 2016 Experiment 7: Synthesis of a Thyroid Hormone Precursor Analog via Electrophilic Aromatic Substitution Reading: Klein 2nd Ed pp 876-879. you will synthesize a thyroid hormone precursor analog via an electrophilic aromatic substitution reaction. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a). so we will use an alternate method of halogenation. Introduction One of the supplements often prescribed to patients with lowered thyroid activity is a combination of iodine and tyrosine. Make sure you correctly calculate the molar amounts of your reactive materials. Page | 26 . 889-893 (Electrophilic Aromatic Substitution). i. 1195-1197 (Amino Acids). the mass you would expect to recover. and its iodination product is a precursor to the essential thyroid hormones (thyroxines) T3 and T4: in fact. and the safety precautions you will take when handling this material. elemental iodine is a controlled substance (see Breaking Bad for why). Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn.e. You will synthesize bromo-4-tert-butylphenol. Tyrosine is a natural amino acid. Place the flask in a sand bath on top of a magnetic stirrer. 3. You will have already determined the R f value of your product from TLC . leave the reaction to heat for another 30 mins. Replace the condenser as soon as you are done! Dilute this sample with 0. as it involves the copper ions. Once cool. assign their configuration as R or S. remove the air condenser from the flask and using a Pasteur pipette. Remove the TLC plate from the chamber and allow the solvent to evaporate completely. Combine the organic layers.10g of copper (II) bromide to the flask.make sure you note this in your lab report. transfer to a 125 mL Erlenmeyer flask and dry using sodium sulfate. Based on these resonance structures and your reading of Klein (p891). Pour the reaction mixture into a separatory funnel and add 10 mL of ethyl acetate. However. Filter the solid and remove the ethyl acetate using rotary evaporation. Analysis of Your Product Weigh your purified product and determine the yield. 4. explain why you obtained your specific product isomer. repeat the TLC analysis: when no 4-tert-butylphenol remains in the reaction. add 15 mL brine and 15mL distilled water to the flask and swirl to mix until the solution turns light blue. (1) Determine the how many stereocenters are present in (-)-tyrosine and.Chem 112B Lab Manual Spring 2016 Experiment 1. Post Lab Questions. Your TA will give you 1H NMR spectra of your product and iodotyrosine for postlab analysis. do you have ortho-bromo-4-tert-butylphenol. Add 1. Hand these in with your postlab report. Spot 4-tert-butylphenol onto the TLC plate for comparison as well. (3) Draw the three most favorable resonance structures of 4-tert-butylphenol. If starting material is still present. 2. (4) The exact mechanism of this reaction is a little complicated. Develop the TLC plate in a TLC chamber using hexane/ethyl acetate (9:1) as the eluent. Using the 1H NMR spectra and the data given in the special section (p44 and 45). determine the structure of your product . Visualize the TLC plate under the UV lamp and analyze the composition of the product mixture. Isolation of Product After the reaction is complete by TLC. or meta-bromo-4-tert-butylphenol? Explain (using the 1H NMR) how you came to your decision. (2) Your TA gave you 1H NMR spectra of your product and iodotyrosine. After 1h. TLC Analysis Of The Reaction Mixture To Determine Reaction Progress After 30 mins heating.5 mL ethyl acetate (in a clean test tube) and apply a small amount of this solution to a TLC plate with a capillary. Attach an air condenser to the flask and heat to 60°C for 1 hour with stirring. obtain a small sample of the reaction mixture (just dip the end of the pipette into the solution and allow capillary action to bring some sample into the end of the pipette). you are ready to isolate your product. Reaction setup Combine 250 mg of 4-tert-butylphenol and 3 mL of acetonitrile in a 50 mL round bottomed flask containing a stir bar. the process involves the formation of small amounts Page | 27 . Be sure to rinse the reaction flask with a small amount of ethyl acetate. using the Cahn-Ingold-Prelog rules.e. remove the flask from the hotplate and allow to cool to room temperature.i. Shake the funnel to mix the layers and extract the aqueous layer with a second 10 mL portion of ethyl acetate. Draw the mechanism of the bromination of 4-tert-butylphenol with Br2. determine which peak in the 1H NMR spectrum corresponds to which proton in the product molecule and iodotyrosine. Page | 28 . (7) Fully assign the two spectra you were given.e. Explain why it is successful with 4-tertbutylphenol.Chem 112B Lab Manual Spring 2016 of bromine in situ.the protons on the -NH2 and-CO2H exchange with the deuterated solvent. (5) If this reaction is attempted with benzene. The two protons from the CH2 group in iodotyrosine show up as two separate peaks in the 1H NMR spectrum. i. (6) The 1H spectrum of iodotyrosine (it is up to you to determine whether it’s ortho or meta compare with the NMR spectrum of your product!) is a little more complicated. Use both chemical shift and coupling analysis to finalize your assignment. Why is this? What is the correct term to describe these protons (see Klein p738)? NOTE . and are missing from the spectrum. nothing happens. 2) Fill in the reaction table below.-eq. you will perform a transacetalization reaction.75 mL) and dichloromethane solvent (3 mL).3-diol as an acetal. add benzaldehyde dimethyl acetal (0.3-diol 0. methanol is formed as byproduct when reacted with 2methylpropane-1. you will perform your first stereoselective reaction by protecting a 1. which can be experimentally irritating. Experiment 1.50 mL 2-Methylpropane-1. pp 939-947 (acetal formation). 2-methyl-1. Instead. Introduction In this experiment. 10-camphorsulfonic acid (5 mg).e. MW mmol 1. and the safety precautions you will take when handling this material. By using benzaldehyde dimethyl acetal as aldehyde surrogate. not the Page | 29 .5.50 mL). Reaction Setup To a 50 mL round bottom flask equipped with a magnetic stirbar.3-propane diol (0.3-diol: this process is far easier to drive to completion. Reaction Scheme. Figure 1.clamp the flask joint. Read these and answer the following questions: a) Which chemical is the most dangerous in this lab? b) Explain why you chose your answer for part a).Chem 112B Lab Manual Spring 2016 Experiment 8: Protecting Groups . Prelab Questions 1) The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. The classical acetalization reaction involves either a diol or multiple alcohols and a carbonyl species such as an alcohol or ketone. This process relies on efficient removal of water from the reaction. i. the mass you would expect to recover. (NOTE . multiple isomers are possible and you will analyze the structure of your product by 1H NMR spectroscopy. assuming 100% conversion to product. which is the limiting reagent in this reaction? 4) Calculate the Theoretical Yield of your product. Make sure you correctly calculate the molar amounts of your reactive materials. Transfer the flask to a sand bath on a magnetic stirrer.00 amount 0.75 mL Camphorsulfonic acid -- -- -- 5 mg Dichloromethane -- -- -- 3 mL product 3) Based on your answers to Q2. As you are forming a sixmembered ring.Synthesis of a Cyclic Acetal Reading: Klein 2nd Ed section 20. name Benzaldehyde Dimethyl Acetal formula mol. Make sure you account for all steps in the mechanism. identify it and explain your reasoning. explain what coupling pattern it has and why it has that pattern. and make sure you use the chair conformation of the 6-membered ring. and transfer the solution into a 125 mL separatory funnel. Remove the spinbar from the flask. Isolation of Product After 30 min of stirring.remember. and add the dichloromethane layer back into the separatory funnel.Chem 112B Lab Manual Spring 2016 condenser!). 3. (8) The 1H NMR peaks corresponding to Ha and Hb in your product (shown on the right) appear at δ 4. Post Lab Questions (1) Draw the mechanism of the reaction. Transfer the filtrate into a weighed 50 mL round-bottomed flask and remove the solvent via rotary evaporation to obtain your product as a clear oil. (5) The 1H NMR spectrum has peaks (marked with "x") for a minor byproduct . You may write "H+" instead of the full structure of camphorsulfonic acid.pressure buildup) and drain the lower layer into a 125 mL Erlenmeyer. Weigh your purified product and determine the yield.what might that be? (6) Why did we use solid camphorsulfonic acid rather than aqueous H2SO4? (7) Identify the peak in the 1H NMR spectrum corresponding to the CH3 group. Hand this in with your postlab report. Transfer the aqueous layer to a different flask.17 and δ 3.50 ppm respectively. as will section 4 of the attached special section) Page | 30 . Rinse the flask with an additional 5 dichloromethane and add the rinse to the separatory funnel. Describe the observed coupling pattern for each peak. 2. add 15 mL dichloromethane to the flask.3-diol starting material.based on your answer to Q3. remove the flask from the hot plate and let the reaction mixture cool to room temperature (~5 min). (4) There is only one major product of this reaction . Add 15 mL distilled water to the separatory funnel. Dry the dichloromethane solution with anhydrous sodium sulfate for 10 mins and filter the solid off using a Hirsch funnel and side-arm flask. (3) Which of those two conformations is the most favorable? Explain your answer. Attach a water-cooled reflux condenser to the flask and heat the reaction mixture at 40°C for 30 mins. Obtain an IR spectrum of your product and the 2methylpropane-1. making sure to keep track of the aqueous and organic layers. Draw them. shake (caution . Your TA will give you a 1H NMR spectrum of your product. This is the organic layer that contains your product . Repeat the aqueous wash two more times with 15 mL distilled water. dichloromethane is heavier than water. Characterization. (2) There are two possible isomers of the product acetal that could conceivably be formed. and explain why the two peaks show different coupling patterns (your chair structures from Q2 may help. Chem 112B Lab Manual Spring 2016 Special Section . Chemically equivalent nuclei have the same resonance frequencies (i. Also chemically equivalent nuclei DO NOT couple to EACH OTHER (they CAN couple to other nuclei. The two CH2 in chloropropane are termed "enantiotopic" protons. This may be achieved in a number of ways: Symmetry: if a molecule is symmetric. notably chemical shift (δ). so the signal will average out – we will see a single peak. appear at the same chemical shift). p 732-772. This only applies if there are no chiral centers in the molecule! Free rotation: free rotation is particularly important for alkyl groups. This type of phenomenon requires discussion of Page | 31 . For NMR basics. 1) Equivalence Before we commence the discussion of coupling constants. magnetic equivalence is a far more complex matter and is beyond this course. The rate of rotation (fs to ps) is very much faster than can be resolved at the timescale of an NMR experiment (ms to s). but what it means here is that the two protons in the CH2 group are identical and have the same chemical shift. just not to each other). the barrier to rotation between the rotamers is very small – at room temperature. Read Klein p737-738 for a full definition. it is important to establish the concept of equivalence of nuclei. etc. then nuclei will have the same chemical shifts as their symmetry counterparts. please read Klein 2nd Ed Ch 16. Nuclei are chemically equivalent when they experience identical chemical environments.NMR Coupling Constants and Variable Patterns NMR Basics: Chemical Shift. we may consider the rotation about the C-C bond to be effectively barrierless (free rotation). Only systems that are chemically equivalent will be covered here. This section assumes you are familiar with the basics of 1H NMR. Generally we speak of two types of equivalence in NMR – chemical and magnetic equivalence. however.e. However. We may perform a conformational analysis of an alkyl group and find that the chemical environment is slightly different for each nucleus. The peak integral corresponds to the area under the peak.8cm.multiply all your heights by 4/3 and you get a Page | 32 . and so cannot be determined by just looking at the spectrum.Chem 112B Lab Manual Spring 2016 a term seen often in NMR experiments – the NMR timescale.2cm:1. You have to convert this ratio so that the sum corresponds to the total #H in your molecule. Stereocenters: If there is a chiral center anywhere in the molecule. In chloropropane.2cm:1. If we integrate the resonance peaks. measure the height of this curve (with a ruler!). This does not apply to CH3 groups . and they couple to each other (see section 4).the three H in CH3 groups are always identical. You will obtain a ratio of heights. this timescale is of the order of ms to s. there are 7 total H . consistent with the number of each type of atom. These protons are termed diastereotopic (Klein p738). we find that the ratio of the peak integrals is equivalent to the ratio of protons resonating to generate that peak. rather than multiple distinct signals. As stated above. Any type of change in the molecule which occurs at a timescale lower than this will lead to an average signal. ALL protons in CH2 groups are different. It is usually represented by a curve above the peaks: How to determine an integral: To determine the integral. each signal with a different chemical shift. Integration of each of the signals gives peak integrals with ratios of 2:2:3. Consider 1-chloropropane: This compound will give rise to three distinct signals. and have different chemical shifts. for example 1. due to a different type of hydrogen atom in the molecule. 2) Peak Integration The intensity of an NMR peak is proportional to the number of protons that resonate at a given frequency. and integrate between these points. If we work the other way. you've added wrong… Other points about integrals: The simple description above holds quite well. and consider the effect of the C-H proton on the resonant frequencies of the methyl group. Peak broadness: Most spectrometers identify the beginnings and ends of peaks by sharp changes in the slope of the obtained spectrum (deviations from baseline). and integration of noisy peaks will often be unsatisfactory. Page | 33 . Consider 1.all protons must be present in a 1H NMR spectrum. We usually set a spectrometer delay time that is much larger than the relaxation time of the slowest signal: for a proton NMR this is usually 5 seconds. There are a number of factors that can cause errors in the integral. If your ratio doesn't add up to the total #H in the molecule. Broad and noisy peaks will often not be well defined for integration purposes. we find that we generate a coupling fine structure that is a doublet – two peaks with relative intensities 1:1. Also note .two 2H peaks. This fine structure is produced by spin-spin coupling.05:1.1-dichloroethane. but it is important to note that the size of the integral is not simply a function of the number of protons corresponding to a resonance peak. We may do this by considering the possible spin states for the hydrogens in the methyl group: Possible Nuclear Spin Configurations for the CH3 group: We will have our signal split into four components.05 protons in your molecule! Some factors are: Relaxation time: most NMR spectrometers acquire spectra using multiple radiofrequency pulses.Chem 112B Lab Manual Spring 2016 ratio of 2:2:3 . 3) Spin-Spin Coupling (Klein p752-758) We know that the localized magnetic field around a nucleus may be affected by the presence of electron density (with its associated magnetic moment) and by the presence of other magnetic nuclei. it doesn't mean there are 1. and one 3H peak. The ratio can also be given to you (the numbers beneath the peaks). If the temporal (time) spacing between the two pulses is not sufficiently large. but it isn't always! Make sure you understand what an integral is. with relative signal intensities (and integrals) of 1:3:3:1 – a quartet. then the system will not be allowed to relax back to its starting state – the signal for the next pulse is correspondingly smaller. Sample dilution: dilute samples will have lower S/N ratios. Be flexible when interpreting integration if the ratio is 1. and let us consider the possible localized magnetic field acting on the single proton in the presence of a free rotating methyl group. there are two types of coupling observed. the further away (through bond) the protons are. Peak intensities of multiplets may be determined by referring to Pascal’s triangle (binomial distribution function): # H on Adjacent C Relative Intensity of Multiplet Multiplicity 0 1 Singlet 1 1 1 2 1 3 1 4 5 1 2 3 4 5 1 1 3 6 10 Doublet Triplet 1 4 10 Quartet 1 5 Quintet 1 Sextet Vicinal and Geminal Protons How far away can the coupling protons be? Generally. 300.) Since the coupling constant is measured in a unit of frequency (Hz). Simply put. The two resonances are a sextet and a triplet . so remember what they mean: Longer range coupling is possible (for example coupling between meta H on an aromatic ring). The coupling constant for the splitting of the C-H resonance signal and the resonance signal for the methyl group must be equal in magnitude. and three for the CH3. etc.six peaks for the CH2. Page | 34 . vicinal and geminal coupling. and is defined by: J = Δδ (ppm) x νinstrument (MHz) where Δδ is the spacing between peaks of the multiplet in ppm and νinstrument is the frequency of the NMR spectrometer (i. How to measure a coupling constant The picture below is of the upfield region of chloropropane (i.e. The multiplicity of a coupled peak is determined by the (2S+1) rule: each individual proton attached to adjacent carbon atoms contributes a spin S of ½.Chem 112B Lab Manual Spring 2016 Three other points need to be made: The resonance frequencies are evenly spaced – the spacing between the peaks is the coupling constant. We will use the words "vicinal" and "geminal" constantly.e. just showing the CH 2 and CH3 groups). i. 400 MHZ. J. Coupling constants smaller than 1 Hz are generally not observed with a common 300 or 400 MHz instrument. We will use this to illustrate how to calculate a coupling constant. but those coupling constants are small and we won't discuss them here. the lower the coupling constant between them. peaks that couple to each other must have the same coupling constant (J). its magnitude is independent of the strength of the magnetic field.e. 9977ppm .0222 ppm. i. To calculate the J value for the triplet.remember that ppm just means 106 and is unitless . three signals are observed: 3H triplet (Ha). 4) Complex Spin-Spin Coupling (Klein p758-760) Coupling Constants are not all the same! The "simple" spin-spin coupling described above refers to vicinal protons that all have the same coupling constant.0235 ppm. multiply this by the magnet frequency (300 MHz in this case . and the exact position of each peak (the "peak pick") is shown above each peak: Think about how you get a triplet .7656 ppm .e.0465ppm and the center peak at 1.e.35 Hz. This usually applies to substituted alkanes . Therefore.7421 ppm = 0.35 Hz. each with the same constant.all the coupling constants are the same. Hence in chloropropane (see above). the J value is the space between each peak (i.multiply ppm by MHz and you get Hz): 0. between the left peak at 1. Page | 35 . 1.both those spaces are the same). i.e.0235 ppm x 300 MHz = 7. or between the center peak at 1. J = 7.0465 ppm . you need two things .0222 ppm and the right peak at 0. i.vicinal to CH3 and CH2).1. 2H sextet (Hb .35 Hz Note that the two J values must be the same . As a rule.there is free rotation about all C-C bond and the distance between the H atoms averages out. This spectrum was taken on a 300 MHz instrument. and the frequency of the spectrophotometer.the exact chemical shift of each peak.Chem 112B Lab Manual Spring 2016 To determine a coupling constant.0222 ppm = 0. and a 2H triplet (2H sextet (Hd . To convert to Hz. the vicinal coupling constant in a substituted alkane will be 7 Hz.35 Hz Repeat with the sextet . 1. J = 7. so the Pascal's Triangle rule applies.e.we'll use the rightmost peaks (the spacings are all the same.the original peak is split by coupling to two H. This will allow you to calculate the J value in Hertz (not ppm!).peaks that couple to each other have the same coupling constant by definition. subtract one value from the other. calculate the spacing between the peaks in ppm. so it doesn't matter which you pick).1.vicinal to CH2 only) .0235 ppm 0.0235 ppm x 300 MHz = 7. and so all three H are different. The relationship between Ha. Hb and Hc is different to that displayed by a normal alkane . and couple to each other with different coupling constants. angle and rigidity. think about what happens when you couple a proton to 2H with the SAME coupling constant. As an exercise. Hc. The alkene group has three protons on it. and there are three corresponding peaks in the NMR spectrum. then the diagram looks like this: Page | 36 . which gives us a triplet. if the coupling constants are different. Hb. We can use the following diagram. Consider a simple alkene.Chem 112B Lab Manual Spring 2016 What happens if the molecule isn't an alkane? Coupling constant magnitude relies on three things distance. 2. just the alkene.there is no rotation around the C=C.9 ppm). The alkene region of the NMR spectrum is shown below.2-dimethylbutene. as we expect: However. Ha. We won't consider the tertbutyl group (a 9H singlet at 0.85 ppm) shows four peaks – this comes from coupling to 2 protons with DIFFERENT coupling constants. Resonance Ha (δ 5. the two coupling constants are: Jb = [δ (peak 1) . the inner peaks are often higher than the outer ones: you can think of this as either "leaning" towards each other.8 Hz Ja = [δ (peak 1) . they're the same. Measuring Coupling constants in a Doublet of Doublets.6 Hz The two coupling constants of 10.again.8 Hz and 17. or forming a "roof" shape (thank the Germans for that one…)."Why are my peaks of different height?" We won't go into this in detail.891 . but coupling effects are more complex than the simple Pascal's Triangle rules we discuss in lecture. This also works for 3/4 . respectively.Hc) and trans (Ha . This is the same procedure as described above.it couples to both Hb and Hc.δ (peak 3)] x 400 MHz = [5.just subtract the shift of peak 2 from that of peak 1. An example of this is shown below: Page | 37 .6 Hz correspond to the cis (Ha . there is no peak at the position of the "1st coupling" lines. Look at the doublet of doublets from our alkene example: Now consider how we determined the coupling pattern: Measuring the small J is easy .Hb) couplings.864] x 400 MHz = 0. but with different J values.044 ppm x 400 MHz = 17.they're the same! Unfortunately.891 . What you do to determine the Ja is subtract the shift of peak 3 from that of peak 1 (or 4 from 2 . If two protons are coupled to each other.027 ppm x 400 MHz = 10. For the alkene example (which was taken on a 400 MHz machine). The easiest effect to use in analyzing 1H NMR spectra is called "leaning" or "roofing".δ (peak 2)] x 400 MHz = [5.5.Chem 112B Lab Manual Spring 2016 Hence Ha shows four lines with the same area (a 1:1:1:1 ratio) . Second Order Effects .847] x 400 MHz = 0.5. You just need to know on which peaks to perform the subtraction. alcohols. you can assume that OH peaks will be broad (and easy to identify) and will not couple to adjacent protons. As we mentioned above. Hence the peak is not sharp and at a single δ.e.Chem 112B Lab Manual Spring 2016 This effect generally occurs when the two peaks are close in chemical shift. and is broad. even solvents such as CDCl3). If not. amide N-H. Why are OH peaks broad? This is a complex subject. they're coupling to other protons. This process may be used to our advantage: if we have a compound that we suspect contains a labile proton. protons attached to electronegative atoms (such as alcohol O-H. and varies with magnet strength. i. The H-bond strength is variable in the solution . In solution. etc. phenols. In a solution. these molecules move around rapidly. For this course.e. An example is shown to the right. then proton/deuterium exchange may occur. changes the chemical shift. H-bonding changes the amount of electron density on the H atom.50 belongs to the CH2 adjacent to the OH. etc) are capable of H-bonding to other H-bond acceptors in solution (i.some molecules have strong contacts and some have weak contacts. however. and only couples to its adjacent CH2. If the compound contains labile protons (eg. an average of the chemical shifts. or variable hydrogen bonding. The reason for this is that many NMR solvents (particularly CDCl3) have a small amount of D2O or DCl in them. but they are all moving around rapidly.e.65 . The 2H triplet at δ 3. but the general answer is either chemical exchange (as described above). this is a complex area. i. so don't expect your doublets and triplets to be exactly level. What you see in an NMR spectrum (and a solution-phase IR. anything with a lone pair. for that matter) is an average of the H-bonding in the solution. FASTER than the NMR timescale. then they can be coupling.this is the OH peak. amines. and there are many exceptions. Most "real" spectra exhibit this to some degree. a carboxylic acid). An additional result of this is that the OH does not couple to adjacent CH protons. but is broad. we can add D2O to the NMR tube and shake it: the disappearance of an NMR signal is usually good evidence for the presence of a labile group such as those listed above. The good thing is that this helps you determine which peaks couple to each other: if the peaks lean towards each other. Page | 38 . not the OH. Exchange Sometimes expected signals may disappear from the 1H NMR spectrum: this may occur for the following types of compounds: carboxylic acids. for 1-hydroxy-4-pentanone: Note the 1H peak at δ 3. 30 ppm.g. etc.g. Aromatic rings with meta directing. and coupling constants between protons that are para to each other are <1 Hz. COOH. and we won't discuss them in depth here. so remember that number! When considering substituted benzene rings. This is easiest to explain for electron donating groups (e. NH2. Some examples of coupling patterns in multisubstituted aromatic Page | 39 .30 ppm. The exact amount of shift from that of benzene depends on the strength of the activating/deactivating group: stronger donors shift the protons more. activating groups (e. NO2). Coupling constants between protons that are ortho to each other are usually 8 Hz. the nature of the substituted group can be determined by the change in chemical shift for the protons on the ring. the coupling constants in different benzene rings are quite consistent.g. The protons ortho and para are shifted further upfield than the meta protons. This causes deshielding of the protons attached to the ring. NO2. no matter the nature of the substituent.30 ppm. We will be comparing all chemical shifts to that of benzene. The protons ortho and para are shifted further upfield than the meta protons. Other groups can be a little complex. CH3. OH. OH) and electron withdrawing groups (e. but they are all shifted upfield from 7.g. and generally cannot be seen. CN. deactivating groups (e. CHO. etc) have protons with δ>7. but they are all shifted upfield from 7.30 ppm. etc) have protons with δ<7. especially halides. Numerical examples: 6) Coupling Patterns in Aromatic Rings You can assign the structure of a substituted benzene ring by looking at the coupling pattern.30 ppm. The result of all this is that aromatic rings with ortho/para directing. and so the protons on benzene display a chemical shift δ = 7. coupling constants between protons that are meta to each other are usually 2 Hz.Chem 112B Lab Manual Spring 2016 5) Chemical Shift Determination in Aromatic Rings The major difference between aromatic rings and aliphatic chains in chemical shift determination is the π electron cloud that resides above and below the benzene ring (Klein p747). As the aromatic ring is flat and there are no angle changes to worry about. OR. Page | 40 .that depends on the nature of the group.these patterns have nothing to do with chemical shift . Coupling is essentially independent of that. B and C are functional groups. where A.Chem 112B Lab Manual Spring 2016 rings are shown below. although there are always exceptions. NOTE . mass of 13C = 13. but different number of neutrons in the nucleus.e. This means that the intensity of the M+1 peak tells you how many carbons are present: (M+1 intensity) = 1. but there are three carbons that can be 13C in propane. so can be ignored.e.1% (i. This is used for WEIGHING bulk amounts of chemicals.e. These have different masses! “Atomic Mass” is the number found in your Periodic Table.011.2% What if M is not the base peak? Page | 41 . 1. The possible isotopes are: Mass = 44: 12CH312CH212CH3 Mass = 45: 13CH312CH212CH3 OR 12CH313CH212CH3 OR 12CH312CH213CH3.5% Dodecane (C12H24): intensity (M+1) = 13. The atomic mass is NOT used in mass spectrometry.0000.1% x 3). All atoms have multiple isotopes – i.1%)2 = 0. so the average mass of carbon atoms is 12. The probability of ONE 13C is 1.3% Pentane (C5H12): intensity (M+1) = 5. same number of protons.0034. Note that the probability of two 13C being present is (1. one for 13C.e.1%.3% (i.1 (M+1) m/z 14 16 18 20 22 M is the Molecular Ion – i. 13C has an abundance of 1.Chem 112B Lab Manual Spring 2016 Isotopes In Mass Spectrometry Mass spectrometry detects the m/z (mass:charge ratio) of each INDIVIDUAL molecule that strikes the detector.e. m/z = 16) looks like this: Relative Abundance / % 100 (M) 1. EACH isotope is detected. More than one Carbon? Propane (CH3CH2CH3) has three carbons. This is the atomic mass of “carbon”. and all have the same mass – the intensity of the M+1 (m/z = 45) peak is 3. so for a mass spectrum of carbon. i. M+1 is the label given to a peak one mass unit larger than the molecular ion.1% of all carbon atoms are 13C). It is the AVERAGE of all known isotopes. CH4+. The INTENSITY of the peaks is proportional to the abundance. the mass of your target molecule. 1.1% x #C Propane (C3H6): intensity (M+1) = 3. you will see TWO peaks – one for 12C. So – a mass spectrum of methane (CH4.012%.: Mass of 12C = 12. just representations): CH3Cl (mass = 50) Relative Abundance / % 100 (M) 32 (M+2) 1.2%. 2-pentanol can fragment in the mass spectrometer.33 (M+3) m/z 50 51 52 53 Page | 42 . losing a CH3 group.1% x #C x (M intensity) So for 2-pentanol. If a molecule contains ONE Bromine atom (e.g. 35Cl / 37Cl and 79Br / 81Br NOTE that the mass difference is 2 amu! Ratio (35Cl / 37Cl) = 75:25 = 100:30 ~ 3:1 Ratio (79Br / 81Br) = 100:98 = 50:49 ~ 1:1 Therefore. M (the molecular ion.1 (M+1) 0. if a molecule contains ONE Chlorine atom (e.g. intensity 100%. N. the base peak is m/z = 75. The important atoms are Cl and Br. you will see an M+2 peak with intensity = M. O. These have two isotopes each. What if other atoms are present? The natural abundance of isotopes of H. The base peak does NOT have to be the molecular ion (and often isn’t).011 x 5 (# of C) = 2. Examples (NOTE – the peak heights are not exact. you will see an M+2 peak with intensity = 1/3 x M. CH3Br).2 (M+1) m/z 74 76 78 80 82 84 86 88 90 The intensity of the M+1 peak is ALWAYS relative to the intensity of M.Chem 112B Lab Manual Spring 2016 The BASE PEAK is the most intense peak in the spectrum and ALWAYS has a relative abundance of 100%. You therefore get a large peak at m/z = 75 as well as the molecular ion at 88: Relative Abundance / % 100 (BASE) 40 (M) 2. m/z = 88) has an intensity of 40% and so M+1 = 40 x 0. F or I is negligible – these can be ignored. CH3Cl). (M+1 intensity) = 1. a molecule with a Cl and more than one C: CH3CH2CH2CH2Cl (mass = 92) Relative Abundance / % 100 (M) 32 (M+2) 4.4 (M+1) 1. M+1 = 13 CH335Cl. 12 CH335Cl.4 (M+3) m/z 92 93 94 95 Page | 43 .Chem 112B Lab Manual Spring 2016 REMEMBER – there are 13C isotopes in this molecule too.1 (M+1) 1.1 (M+3) m/z 94 95 96 97 Finally. So M = 12 CH337Cl and M+3 = 13CH337Cl. M+2 = CH3Br (mass = 94) Relative Abundance / % 100 (M) 98 (M+2) 1. u.011 14. It is the AVERAGE of all known isotopes.0034 14.9949 1.m.Chem 112B Lab Manual Spring 2016 Table of Elemental Masses Element Hydrogen Isotope 1 H C 13 C 14 N 16 O 12 Carbon Nitrogen Oxygen Fluorine 19 F Cl 37 Cl 79 Br 81 Br 127 I 35 Chlorine Bromine Iodine Unit Mass (a.904 “Atomic Mass” is the number found in your Periodic Table.0067 15.9994 18.9984 35.m.4527 79.0079 19 35 37 79 81 127 18.9045 12. Use the Isotopic Mass! DO NOT USE ATOMIC MASS WHEN ANALYZING MASS SPECTRA!!!! Page | 44 . It is NOT used in mass spectrometry.9688 36.0000 13.00783 12.9163 126.) “Atomic Mass” 1 12 13 14 16 1.u. This is used for WEIGHING bulk amounts of chemicals. you are looking at ONE ISOTOPE.904 126.0031 15.9659 78.9984 34. In mass spectrometry.9183 80.) Isotopic Mass (a.