Phenols and Ethers TOP Concepts: 1. PHENOLS AND ETHERS Alcohols.CHEMISTRY ALCOHOLS.com 2 . phenols and ethers 2. Structure of alcohols. Preparation of alcohols www.topperlearning. the boiling points decrease with increase in branching in the carbon chain. PHENOLS AND ETHERS 3. This is because of increase in van der Waals forces with increase in the surface area. Physical properties of alcohols and phenols a. Boiling points: Boiling points of alcohols and phenols are higher in comparison to other classes of compounds. Preparation of phenols 4. In alcohols. This is because of decrease in van der Waals forces with decrease in the surface area. namely hydrocarbons. www. haloalkanes and haloarenes of comparable molecular masses.com The boiling points of alcohols and phenols increase with increase in the number of carbon atoms. 3 .CHEMISTRY ALCOHOLS.topperlearning. This is because the –OH group in alcohols and phenols is involved in intermolecular hydrogen bonding. ethers. Chemical properties of alcohols a. Reaction with metals: b. 5. Reactions of alcohols and phenols involving cleavage of O–H bond a. The solubility of alcohols decreases with increase in the size of alkyl/aryl (hydrophobic) groups. Esterification: www.topperlearning. Solubility Alcohols and phenols are soluble in water due to their ability to form hydrogen bonds with water molecules. Reactions involving cleavage of O–H bond: Alcohols react as nucleophiles b. Reactions involving cleavage of carbon–oxygen (C–O) bond in alcohols: Protonated alcohols react as electrophiles c. Oxidation 6. Dehydration d.CHEMISTRY ALCOHOLS.com 4 . PHENOLS AND ETHERS b. Reaction with hydrogen halides: conc.573K or KMnO4 Tertiary alcohol Alkene Acidified potassium permanganate Alcohol Carboxylic acid www. PHENOLS AND ETHERS 7. Reactions of alcohols involving cleavage of the carbon–oxygen (C–O) bond: a.573K or CrO3 alcohol Ketone Cu.573K or CrO3 or PCC Pr imary alcohol Aldehyde Secondary Cu.topperlearning.com 5 .CHEMISTRY ALCOHOLS. Dehydration: c.HCl ZnCl 2 RX + H O ROH + HX Lucas reagent 2 b. Oxidation: Cu. Reaction with phosphorus trihalides: 3ROH + PX3 → 3R–X + H3PO3 (X = Cl. Br) c. The ionisation of an alcohol and a phenol occurs as follows: www. The sp2 hybridised carbon has higher electronegativity than the sp3 hybridised carbon. the hydroxyl group is directly attached to the sp2 hybridised carbon of the benzene ring which acts as an electron-withdrawing group. Whereas in alcohols. This decreases the polarity of the O–H bond.topperlearning. the hydroxyl group is attached to the sp3 hybridised carbon of the alkyl group. the polarity of the O–H bond of phenols is higher than that of alcohols. PHENOLS AND ETHERS 8. Thus. or it has electron-releasing inductive effect (+I effect). the acid strength decreases. Acidic nature a. Chemical properties of phenols 9. Hence. Phenol > H2O > Primary alcohol > Secondary alcohol > Tertiary alcohol The acidic character of alcohols is due to the polar nature of the O–H bond.CHEMISTRY ALCOHOLS. Whereas in alcohols.com 6 . the ionisation of phenols is higher than that of alcohols. the hydroxyl group is directly attached to the sp2 hybridised carbon of the benzene ring. Phenol is more acidic than alcohol because In phenol. the electron density on oxygen increases. The alkyl group is an electron-releasing group (–CH3. –C2H5). Hence. b. Due to the +I effect of alkyl groups. the hydroxyl group is attached to the alkyl group which has an electron-releasing inductive effect. In phenol. If it is a secondary alcohol.topperlearning.HCl ZnCl 2 RCl + H O ROH + HCl Lucas reagent 2 If it is a primary alcohol. the negative charge is localised on oxygen. The delocalisation of the negative charge makes the phenoxide ion more stable and favours the ionisation of phenol. How to distinguish between some important pair of organic compounds a. while in phenoxide ion. then no turbidity appears at room temperature. decrease the acidic strength. then turbidity appears immediately. whereas alcohols do not give purple colour. c. such as alkyl groups. then turbidity appears in 5 minutes. secondary and tertiary alcohol: Lucas reagent test: conc. Although there is charge delocalisation in phenol. PHENOLS AND ETHERS In alkoxide ion. electron-releasing groups. 6C6H5OH + Fe3+ → [Fe(OC6H5)6]3− + 6H+ Purple colour b. 10. Phenol and alcohol: Phenol on reaction with neutral FeCl3 gives purple colour. Primary.CHEMISTRY ALCOHOLS. the charge is delocalised. On the other hand. the presence of electron-withdrawing groups such as the nitro group enhances the acidic strength of phenol. Turbidity appears only on heating. If it is a tertiary alcohol.com 7 . It is because electron-withdrawing groups lead to effective delocalisation of the negative charge in the phenoxide ion. its resonance structures have charge separation due to which the phenol molecule is less stable than the phenoxide ion. In substituted phenols. www. CH3OH + I2+ NaOH No yellow ppt.topperlearning. Boiling points: Ethers have much lower boiling points than alcohols. C2H5OH + 4I2+ 6NaOH CHI3 + 5NaI + 5H 2O + HCOONa Yellow ppt. Physical properties of ethers a. This is due to the presence of hydrogen bonding in alcohols. Methanol and ethanol: Iodoform test: Ethanol when reacted with I2 and NaOH or NaOI gives a yellow ppt.CHEMISTRY ALCOHOLS. Preparation of ethers 12. 11. This is because similar to alcohols. PHENOLS AND ETHERS a. of iodoform because of the presence of the CH3–CH (OH)− group. Miscibility: Miscibility of ethers with water resembles those of alcohols of the same molecular mass. www.com 8 . b. oxygen of ether can also form hydrogen bonds with the water molecule. Hydrogen bonding is absent in ethers. CHEMISTRY ALCOHOLS. then the alkyl halide is always tertiary.topperlearning. If a tertiary alkyl group is present. Cleavage of C–O bond in ethers: R–O–R’ + HX → R–X + R’OH Excess The order of reactivity of hydrogen halides is as follows: HI > HBr > HCl The alkyl halide formed is always the lower alkyl group. In phenolic ethers.com 9 . the cleavage occurs with the formation of phenol and alkyl halide. Electrophilic substitution reaction in aromatic ethers: www. PHENOLS AND ETHERS 13. b. Chemical properties of ethers a. Alcohol from Grignard’s reagent: R' R' H2O H2O RCHO R 'MgX RCH OMgX RCH OMgX Mg(OH)X www. Some important reactions for conversions a.topperlearning. PHENOLS AND ETHERS 14.com 10 . Conversion 2: c. Conversion 1: b.CHEMISTRY ALCOHOLS.
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