Question

Assertion: $\mathrm{KCN}$ reacts with methyl chloride to give methyl isocyanide.

Reason: ${\mathrm{CN}}^{-}$ is an ambident nucleophile.

• A. Assertion is true, but Reason is false.
• B. Assertion is false, but Reason is the correct statement.
• C. Both Assertion and Reason are true. The reason is the correct explanation of Assertion.
• D. Both Assertion and Reason are true. The reason is not the correct explanation of Assertion.

Answer 1

The correct option is B

Assertion is false, but Reason is the correct statement.

Explanation of correct option

(B) Assertion is false, but Reason is the correct statement.

• $\mathrm{KCN}$ is predominantly ionic and provides cyanide ions in solution.
• Although both nitrogen and carbon atoms are in a position to donate electron pairs, the attack takes place mainly through the carbon atoms and not through the nitrogen atom since $\text{C—C}$ bond is more stable than $\mathrm{C}—\mathrm{N}$ bond.
• Because of the stable $\text{C—C}$ bond in methyl cyanide,$\mathrm{KCN}$ combines with methyl chloride $\left({\mathrm{CH}}_3\mathrm{Cl}\right)$ to produce a combination of methyl cyanide and methyl isocyanide, with methyl cyanide being predominant.
• The chemical reaction between $\mathrm{KCN}$ and ${\mathrm{CH}}_3\mathrm{Cl}$ can be depicted as:

$\mathrm{KCN}\left(\mathrm{s}\right)+{\mathrm{CH}}_3\mathrm{Cl}\left(\mathrm{aq}\right)\to {\mathrm{CH}}_3\mathrm{CN}\left(\mathrm{aq}\right)+\mathrm{KCl}\left(\mathrm{s}\right)$

Ambidentate nucleophile

• "Groups like cyanides and nitrites possess two nucleophilic centers and are called ambident nucleophiles".
• Actually, the cyanide group is a hybrid of two contributing structures and therefore can act as a nucleophile in two different ways.

Hence, the reason is the correct statement.

Explanation of incorrect options

The assertion is false, but Reason is the correct statement. Hence, the options (A), (C), and (D) are incorrect.

Therefore, the correct option is (B). The assertion is false, but Reason is the correct statement.