Radical Cyanation Mechanism of Ethanol

Steps:

• Recognize the reaction involves HCN and NaCN, suggesting a radical pathway for C-H substitution in ethanol.
• Examine choices for initiation, propagation, and termination steps typical of radical mechanisms.
• Eliminate options lacking complete radical sequences or incorrect products.
• Select B for its coherent propagation leading to CH3CH2H (ethane) and cyanide radical.

Why B is correct:

• B depicts a radical propagation where ethanol loses H• to form CH3CH2•, then abstracts from another molecule, aligning with homolytic cleavage in HCN-initiated reactions.

Why the others are wrong:

• A: Shows invalid cyanohydrin formation on non-carbonyl ethanol, with unbalanced arrows.
• C: Lacks cyanide involvement and radical notation, incomplete mechanism.
• D: Misrepresents initiation (HCN doesn't homolyze easily) and propagation products.

Final answer: B