Concept:The carbonyl group (\( C=O \)) features an electrophilic carbon atom due to the electronegative oxygen pulling the pi electrons away from it.
Solution:- In the reaction with \( HCN \), the attacking species is the cyanide nucleophile (\( CN^- \)).
- The nucleophile attacks the partially positive carbonyl carbon, breaking the \( \pi \) bond and transferring the electrons onto oxygen.
- Oxygen is subsequently protonated to form an alcohol group. Since two molecules (acetone and HCN) combine completely to form one molecule (a cyanohydrin) without any leaving group, the mechanism is a Nucleophilic addition.
Why other options are incorrect:Electrophilic addition is typical of non-polar \( C=C \) bonds. Substitution reactions require an atom or group to leave, which does not happen in cyanohydrin formation.
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