Nucleophilic Addition to Carbonyl Groups

Steps:

• Aldehydes and ketones contain a polar C=O bond, making the carbon electrophilic.
• HCN + NaCN generates CN⁻, a strong nucleophile.
• CN⁻ attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate.
• Protonation yields the cyanohydrin product via addition.

Why C is correct:

• Nucleophilic addition occurs when a nucleophile like CN⁻ bonds to the electrophilic carbonyl carbon, following the mechanism for carbonyl reactions (e.g., R₂C=O + CN⁻ → R₂C(OH)CN).

Why the others are wrong:

• A: Electrophilic addition involves an electrophile attacking a nucleophilic site like alkenes, not the electrophilic carbonyl carbon.
• B: Electrophilic substitution replaces a hydrogen or group on an aromatic ring, irrelevant to carbonyl addition.
• D: Nucleophilic substitution requires a leaving group to depart, but no such group exists in carbonyls for this reaction.

Final answer: C