Question

The major products A and B formed in the following reaction are:

• A. \(A=\mathrm{CH_3CH_2CN}\), \(B=\mathrm{CH_3CH_2NC}\)
• B. \(A=\mathrm{CH_3CH_2CN}\), \(B=\mathrm{CH_3CH_2CN}\)
• C. \(A=\mathrm{CH_3CH_2NC}\), \(B=\mathrm{CH_3CH_2NC}\)
• D. \(A=\mathrm{CH_3CH_2NC}\), \(B=\mathrm{CH_3CH_2CN}\)

Hint:

KCN gives nitriles (\(-CN\)) whereas AgCN gives isocyanides (\(-NC\)). This is one of the most frequently asked reactions in haloalkanes.

Answer 1

The Correct Option is A

Step 1: Reaction with KCN.
KCN is predominantly ionic. \[ KCN \rightarrow K^+ + CN^- \] The carbon end of cyanide carries greater electron density and attacks the alkyl halide. Hence nitrile is formed. \[ CH_3CH_2Br + KCN \rightarrow CH_3CH_2CN \] Thus, \[ {A=CH_3CH_2CN} \]

Step 2: Reaction with AgCN.
AgCN is largely covalent. The carbon atom remains coordinated to silver and the nucleophilic attack occurs mainly through nitrogen. Therefore isocyanide is formed. \[ CH_3CH_2Br + AgCN \rightarrow CH_3CH_2NC \] Thus, \[ {B=CH_3CH_2NC} \]

Step 3: Write the final products.
\[ A=CH_3CH_2CN \] \[ B=CH_3CH_2NC \] Hence, \[ {\text{Option (A)}} \]