CBSE Class 12 · 2020 · Alcohols Phenols and EthersLong Answer

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(a) Give the mechanism for the formation of ethanol from ethene. (2)
(b) Predict the reagent for carrying out the following conversions: (1×3)
(i) phenol to benzoquinone
(ii) anisole to p-bromoanisole
(iii) phenol to 2,4,6-tribromophenol

Solution

(a) Acid hydration mechanism:

CH $_{2}$ =CH $_{2}$ + H $^{+}$ → CH $_{3}$ CH $_{2}^{+}$ (slow, rate-determining).
H $_{2}$ O attacks the cation → CH $_{3}$ CH $_{2}$ \overset{+}{O}H $_{2}$ .
Loss of H $^{+}$ → CH $_{3}$ CH $_{2}$ OH.

(b)(i) \textbf{Na

_{2}

_{2}

_{7}

_{2}

_{4}

} (chromic acid) → p-benzoquinone.
(ii) \textbf{Br

_{2}

in ethanoic acid} — mono-bromination, para major.
(iii) \textbf{Bromine water} (excess) → white 2,4,6-tribromophenol.

CBSE Class 12 Board · 2020 · Subjective

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