During the specific nucleophilic addition of sodium bisulphite () to aldehydes and ketones, which atom acts as the primary nucleophilic center that directly attacks the carbonyl carbon?

Question

During the specific nucleophilic addition of sodium bisulphite ($NaHSO_3$) to aldehydes and ketones, which atom acts as the primary nucleophilic center that directly attacks the carbonyl carbon?

Prashant Kotian · Accepted Answer

Correct answer: D. In the bisulphite ion (), the negative charge is distributed among the oxygen atoms via resonance. However, the Sulfur atom has a lone pair and is less electronegative/more polarizable, making the S-site significantly more nucleophilic than the O-site. Thus, Sulfur attacks the carbon.

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