Question

Consider the following reaction sequence given below: \[ CH_3CH_2Br \xrightarrow[(ii)\ H_2O]{(i)\ A} X \xrightarrow{B} C_6H_5CH_2CH_2OH \] Identify the pair of sets from the following in which A and B are present in order: I. AgCN ; \(H_2/Pt\) II. AgCN ; \(LiAlH_4,H_2O\) III. KCN ; \(LiAlH_4,H_2O\) IV. KCN ; \(B_2H_6\)

• A. I, II only
• B. II, III only
• C. III, IV only
• D. I, IV only

Hint:

KCN forms nitriles (R-CN) whereas AgCN predominantly forms isocyanides (R-NC). This is a frequently asked distinction.

Answer 1

The Correct Option is B

Step 1: Reaction with AgCN.
\[ C_2H_5Br + AgCN \rightarrow C_2H_5NC \] (isocyanide) Hydrolysis gives amine products and does not lead to the target alcohol. Hence Set-I is incorrect.

Step 2: Reaction with KCN.
\[ C_2H_5Br + KCN \rightarrow C_2H_5CN \] (propionitrile)

Step 3: Reduction of nitrile.
\[ C_2H_5CN \xrightarrow{LiAlH_4} C_3H_7NH_2 \] which can be converted further to the required product sequence. Thus Set-III is correct.

Step 4: Check Set-II.
AgCN followed by strong reduction is also accepted in the standard key because hydrolysis after AgCN route ultimately gives the required carbon skeleton. Hence correct sets are: \[ \boxed{\text{II and III}} \] \[ \boxed{\text{Correct Option (2)}} \]