Benzyl isocyanide can be obtained by :
A.
B.
C.
D.
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 3 steps

For an isocyanide you need nitrogen bonded to carbon: AgCN on a halide, or chloroform and KOH on a 1° amine.

1. Two routes. An isocyanide, R-N≡C, has the alkyl group on nitrogen. You can make it by alkylating cyanide at its N end with AgCN, or by the carbylamine reaction, which works only for primary amines.
2. Which end attacks. AgCN is largely covalent, so the carbon end is tied up with silver and the free nitrogen lone pair attacks, giving R-NC. KCN is ionic, so the free CN⁻ attacks through the more nucleophilic carbon, giving the nitrile R-CN.

   Reaction	What happens	Benzyl isocyanide?
   A: C₆H₅CH₂Br + AgCN	N end of covalent AgCN attacks, giving C₆H₅CH₂-NC	Yes
   B: C₆H₅CH₂NH₂ + CHCl₃/KOH	1° amine gives the carbylamine reaction, C₆H₅CH₂-NC	Yes
   C: C₆H₅CH₂NHCH₃ + CHCl₃/KOH	2° amine has only one N–H, so no isocyanide forms	No
   D: C₆H₅CH₂OTs + KCN	Ionic CN⁻ attacks through C, giving C₆H₅CH₂-CN	No (nitrile)

3. So. Only A and B give benzyl isocyanide, so the answer is (c).

The idea to keep. AgCN gives isocyanides and KCN gives nitriles. The carbylamine test works only for 1° amines, because the nitrogen must lose both of its H atoms to form R-NC.

Answer from the NTA final answer key. Solution by PrepWiser.