Cyanohydrin Formation by Nucleophilic Addition

Steps:

• Carbonyl compounds like aldehydes (RCHO) or ketones (R₂CO) have a polar C=O bond, with electrophilic carbon.
• HCN dissociates to provide CN⁻ nucleophile, which attacks the carbonyl carbon.
• The oxygen gains a proton, forming a cyanohydrin (RCH(OH)CN or R₂C(OH)CN).
• The diagram's structure shows two carbon substituents on the product carbon, indicating X is a ketone (R₂C=O).

Why D is correct:

• Nucleophilic addition to ketones follows the mechanism where CN⁻ adds to R₂C=O, yielding R₂C(OH)CN, matching the product's functional group and structure.

Why the others are wrong:

• A: Electrophilic addition is incorrect; the carbonyl carbon acts as electrophile, attacked by nucleophile CN⁻, not vice versa; aldehyde irrelevant here.
• B: Electrophilic addition wrong; mechanism is nucleophilic, though ketone is correct.
• C: Nucleophilic addition correct, but X is ketone (two R groups), not aldehyde (one R and one H).

Final answer: D