Reaction types in alcohol to nitrile conversion

Steps:

• First step (X): CH3CH2OH to CH3CH2Br replaces OH with Br using reagent like HBr or PBr3; Br⁻ acts as nucleophile attacking the carbon, displacing H2O.
• Second step (Y): CH3CH2Br to CH3CH2CN replaces Br with CN using KCN; CN⁻ acts as nucleophile attacking the carbon, displacing Br⁻.
• Both are SN2 mechanisms typical for primary alkyl compounds.
• Eliminate options with free-radical (alkane halogenation) or electrophilic substitution (aromatic rings).

Why B is correct:

• Option B matches both steps as nucleophilic substitution, where a nucleophile bonds to an electrophilic carbon, displacing a leaving group (per SN2 definition).

Why the others are wrong:

• A: Free-radical substitution applies to alkanes like chlorination of methane, not alcohol conversion; electrophilic substitution is for benzene derivatives.
• C: Second step is nucleophilic (CN⁻ attacks), not electrophilic substitution.
• D: Identical to C, so second step incorrectly labeled electrophilic.

Final answer: B