See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: KCN is an ambident nucleophile, meaning it can attack through either carbon (giving cyanide, -CN) or nitrogen (giving isocyanide, -NC). The major product depends on which end preferentially attacks the substrate. Step 1: Identify the substrate and reagent. Benzyl chloride (C6H5-CH2-Cl) is a primary alkyl halide. KCN in ethanol provides the cyanide ion (CN-) as the nucleophile. Step 2: Determine the preferred site of attack of CN-. Cyanide ion is a soft nucleophile and carbon is the softer end (carbon bears the negative charge more effectively in terms of polarizability). Primary alkyl halides like benzyl chloride undergo SN2 reactions. Carbon of CN- attacks the electrophilic carbon of benzyl chloride preferentially because carbon is the more polarizable (softer) end of the ambident nucleophile, and it forms a stronger C-C bond thermodynamically. Step 3: Product formed. Attack of carbon of CN- on the CH2 of benzyl chloride displaces Cl- and gives C6H5-CH2-CN, which is benzyl cyanide (also known as phenylacetonitrile). Step 4: Why not isocyanide? Isocyanide (C6H5-CH2-NC) would form if nitrogen attacked. Nitrogen attack is favored in polar aprotic solvents and with harder electrophiles. With primary alkyl halides under normal conditions (ethanolic KCN), carbon attack predominates giving the thermodynamically and kinetically preferred cyanide product. Step 5: Why not other options? (a) Benzyl ethyl ether would require reaction with ethoxide, not cyanide. (b) Benzyl alcohol would require hydrolysis conditions. These reagents are not relevant here. Therefore, the correct answer is C.