Nucleophilic addition to aldehydes with HCN under basic conditions

Steps:

• Recognize nucleophilic addition involves electron-rich species attacking an electron-deficient center, common in carbonyls.
• Eliminate options without carbonyls: A and B involve alkyl halides, favoring substitution or elimination.
• Focus on C and D: both feature propanal (aldehyde) with HCN, but check conditions for mechanism and yield.
• Alkaline conditions generate CN⁻ nucleophile for efficient addition; acidic conditions protonate CN⁻, reducing yield.

Why C is correct:

• Under alkaline conditions, CN⁻ adds to propanal's carbonyl carbon, forming a stable cyanohydrin via nucleophilic addition (rate depends on [CN⁻]).

Why the others are wrong:

• A: Hot ethanolic NaOH promotes E2 elimination in 1-bromopropane, yielding alkene, not addition.
• B: Alkaline HCN with secondary 2-iodopropane undergoes SN1 substitution, not addition to a carbonyl.
• D: Acidic conditions protonate HCN to HCN, preventing nucleophilic CN⁻ formation and yielding poor cyanohydrin.

Final answer: C