Identify the likely reaction sequence

In standard haloalkane/haloarene conversions, a benzylic compound is often prepared first and then reacted with cyanide-type reagents.

The key distinction is:

• With alcoholic KCN, alkyl halides generally give nitriles: $R{-}CN$
• With AgCN, alkyl halides generally give isocyanides: $R{-}NC$

Determine compound A

Since the second step must involve substitution by $CN$ or $NC$, compound $A$ should be a benzyl halide, not benzyl alcohol, because benzyl alcohol does not directly give these products under the usual cyanide substitution conditions.

Thus, $A = \text{benzyl chloride } (C_6H_5CH_2Cl)$

Determine compound B

If benzyl chloride reacts with AgCN, the nitrogen end attacks preferentially because AgCN is largely covalent. Hence the product is isocyanide: $C_6H_5CH_2Cl \xrightarrow{AgCN} C_6H_5CH_2NC$

Therefore, $B = \text{benzyl isocyanide}$

Match with options

• A: $A=$ benzyl alcohol, $B=$ benzyl cyanide $\quad \times$
• B: $A=$ benzyl chloride, $B=$ benzyl cyanide $\quad \times$
• C: $A=$ benzyl alcohol, $B=$ benzyl isocyanide $\quad \times$
• D: $A=$ benzyl chloride, $B=$ benzyl isocyanide $\quad \checkmark$

Final answer

The compounds are: $A = \text{benzyl chloride}, \qquad B = \text{benzyl isocyanide}$

So the correct option is D.