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CBSE Class 12 · 2001 · All India Compartment · Alcohols Phenols and EthersShort Answer

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a) Give reasons for the following: phenol does not undergo protonation readily.
b) Give a chemical test to distinguish between the following pair of compounds: 2-butanol and 2-methyl-2-propanol.

Solution

(a) In phenol the oxygen lone pairs are tied up in resonance with the ring; the reduced electron density on O makes it a poor proton acceptor — protonation is difficult.
(b) Lucas reagent (conc. HCl + anhydrous ZnCl):
2-methyl-2-propanol (tertiary) — turbidity \textbf{immediately};
2-butanol (secondary) — turbidity after \textbf{about 5 minutes}.

CBSE Class 12 Board · 2001 · All India Compartment · Subjective

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