How would you account for the following?
i) Phenols are much more acidic than alcohols.
ii) The boiling points of ethers are much lower than those of alcohols of comparable molar masses.
i) Phenols are much more acidic than alcohols.
ii) The boiling points of ethers are much lower than those of alcohols of comparable molar masses.
Solution
(i) The phenoxide ion spreads its negative charge over the ring (resonance), so phenol ionises readily; an alkoxide keeps the charge on one oxygen, intensified by the alkyl +I — alcohols barely ionise. Hence phenols ≫ alcohols in acidity.
(ii) Alcohol molecules associate through O–H···O hydrogen bonds, which must be broken on boiling; ethers lack an O–H and are held only by weak dipole/van der Waals forces — so, for similar masses, ethers boil far lower (ethanol 351 K vs methoxymethane 249 K).
(ii) Alcohol molecules associate through O–H···O hydrogen bonds, which must be broken on boiling; ethers lack an O–H and are held only by weak dipole/van der Waals forces — so, for similar masses, ethers boil far lower (ethanol 351 K vs methoxymethane 249 K).
CBSE Class 12 Board · 2007 · Delhi · Subjective