The compounds A and B in the following reaction are, respectively:

Step 1: Formation of Compound A (Blanc Chloromethylation)

When benzene reacts with formaldehyde (HCHO) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst like ZnCl2, it undergoes a Blanc chloromethylation reaction.

• Mechanism: Formaldehyde is protonated to form an electrophile, which attacks the benzene ring. The resulting benzyl alcohol intermediate is quickly converted by HCl into a benzyl halide.
• Compound A: Benzyl chloride (C6H5-CH2Cl)

Step 2: Formation of Compound B (Nucleophilic Substitution with AgCN)

When benzyl chloride (A) reacts with silver cyanide (AgCN), a nucleophilic substitution reaction takes place.

• Regioselectivity Rule: Silver cyanide (AgCN) is predominantly covalent in nature. Because the silver-carbon bond is strong, the lone pair on the nitrogen atom acts as the nucleophile rather than the carbon atom.
• Result: This leads to the formation of an isocyanide (isonitrile) rather than a cyanide (nitrile).
• Compound B: Benzyl isocyanide (C6H5-CH2-NC)

Summary of Products

• A: Benzyl chloride (C6H5-CH2Cl)
• B: Benzyl isocyanide (C6H5-CH2-NC)