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JEE Main levelSingle correct optionDifficulty 2 of 3co036

The rate of formation of an oxime from acetone and $NH X_{2} OH$ is greatest near pH 4.5 and falls at both lower and higher pH. The best explanation is

Athe reaction is catalysed only by $OH X^{-}$ , which is optimal near pH 4.5
Bat lower pH the nucleophile is protonated, at higher pH there is too little acid to catalyse dehydration of the carbinolamine
Cat lower pH the carbonyl group is reduced, at higher pH the oxime hydrolyses to a nitrile
Dat higher pH $NH X_{2} OH$ is protonated, at lower pH acetone enolises completely

Answer: B

In strong acid

NH X_{2} OH

is converted to the non-nucleophilic

NH X_{3} OH X^{+}

. In weak acid or base, the loss of water from the tetrahedral carbinolamine lacks acid catalysis, so the maximum lies in between.

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