Which of the following nucleophilic additions to the carbonyl group are essentially IRREVERSIBLE under the reaction conditions (before work-up)?

Aaddition of $CN X^{-}$ to a ketone to give the cyanohydrin anion
Baddition of hydride from $LiAlH X_{4}$ to a ketone
Caddition of methanol to an aldehyde under acid catalysis
Daddition of $CH X_{3} MgBr$ to a ketone

Answer: B, D

Carbanion and hydride are very poor leaving groups, so the alkoxide formed by

R X^{-}

H X^{-}

addition does not expel them. Cyanide and alcohols are good leaving groups from the tetrahedral intermediate, so cyanohydrin and hemiacetal formation are reversible equilibria.

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Which of the following nucleophilic additions to the carbonyl group are essentially IRREVERSIBLE under the reaction conditions (before work-up)?

Answer: B, D

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