See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: Nucleophilic substitution (SN2) reactions of alkyl halides with sodium cyanide (NaCN). The cyanide ion (CN⁻) is a good nucleophile that attacks electrophilic carbon centers via SN2 mechanism. Step 1: Identify the substrate. 4-Bromobenzyl chloride has the structure: a benzene ring with a bromo substituent at the para (4) position, and a -CH2Cl (benzyl chloride) group at position 1. Step 2: Identify the reactive site. There are two C-halogen bonds: the aryl C-Br bond (on the ring) and the benzylic C-Cl bond (-CH2Cl). Aryl halides are generally unreactive toward SN2 under mild conditions because the carbon is sp2 hybridized and the back-side attack is blocked by the ring. The benzylic C-Cl bond, however, is highly reactive toward SN2 because the benzylic position is activated and the primary carbon is accessible. Step 3: Reaction outcome. CN⁻ attacks the benzylic carbon (CH2Cl) in an SN2 reaction, displacing Cl⁻ and introducing the CN group at the benzylic position. The aryl C-Br bond remains intact. Step 4: Product. The product retains the bromo group on the ring at position 4 and has a -CH2CN (cyanomethyl/benzyl cyanide) group instead of -CH2Cl. This compound is named 4-bromobenzyl cyanide. Why other options fail: - (b) 4-cyanobenzyl chloride would require substitution at the aryl C-Br position, which does not occur under these mild SN2 conditions. - (c) 4-cyanobenzyl cyanide would require substitution at both the aryl C-Br and benzylic C-Cl positions, which is not feasible under these conditions. - (d) 4-bromo-2-cyanobenzyl chloride implies CN insertion at the ortho position of the ring, which does not occur via SN2. Therefore, the correct answer is A.