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CBSE Class 12 · 2020 · Alcohols Phenols and EthersLong Answer

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(a) Out of t-butyl alcohol and n-butanol, which one undergoes acid-catalysed dehydration faster, and why? (2)
(b) Carry out the following conversions: (1×3)
(i) phenol to salicylaldehyde
(ii) t-butyl chloride to t-butyl ethyl ether
(iii) propene to propanol

Solution

(a) \textbf{t-Butyl alcohol} dehydrates faster: ionisation gives the stable tertiary carbocation (rate 3° > 2° > 1°).
(b)(i) Reimer–Tiemann: CHCl + NaOH(aq) at 340 K, then acidify → salicylaldehyde.
(ii)

(the 1° halide must be the S2 partner, or elimination wins).
(iii) Hydroboration–oxidation: BH, then HO/OH → CHCHCHOH.

CBSE Class 12 Board · 2020 · Subjective

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