CBSE Class 12 · 2017 · Alcohols Phenols and EthersShort Answer

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(a) Arrange the following compounds in increasing order of their acid strength: p-cresol, p-nitrophenol, phenol.
(b) Write the mechanism (using curved-arrow notation) of the following reaction:

C H_{2} = C H_{2} H_{3} O^{+} C H_{3} C H_{2}^{+} + H_{2} O

Solution

(a) –CH

_{3}

(+I) destabilises the phenoxide, –NO

_{2}

(−I, −M) stabilises it:

p - cresol < phenol < p - nitrophenol

(b) Electrophilic protonation of the alkene:
the C=C π-pair swings onto one carbon's H of H

_{3}

^{+}

(curved arrow from the double bond to H), the O–H pair falling back onto oxygen —

C H_{2} = C H_{2} + H - O + H_{2} \to C H_{3} - C H_{2}^{+} + H_{2} O

forming the ethyl carbocation (the first step of acid hydration).

CBSE Class 12 Board · 2017 · Subjective

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