Assertion (A): Haloalkanes react with KCN to form alkyl cyanides as a main product while with AgCN form isocyanide as the main product.

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Solution

Q.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). [2024]
Assertion (A): Haloalkanes react with KCN to form alkyl cyanides as a main product while with AgCN form isocyanide as the main product.

Reason (R): KCN and AgCN both are highly ionic compounds.

In the light of the above statements, choose the most appropriate answer from the options given below:

1 (A) is correct but (R) is not correct

2 Both (A) and (R) are correct but (R) is not the correct explanation of (A)

3 (A) is not correct but (R) is correct

4 Both (A) and (R) are correct and (R) is the correct explanation of (A)

Ans.
(1)

KCN is an ionic compound and predominantly exists as $K^{+}$ and $C N^{-}$ . In $C N^{-}$ both C and N have lone pairs ${}^{(-)}{(\overset{∙ ∙}{C} \equiv N)}$ and can participate in nucleophilic substitution reactions with haloalkanes. But C donates its lone pair in preference to N and cyanide is formed as chief product.

AgCN is a covalent compound; hence, carbon does not have a free lone pair to react ${(Ag - C \equiv N)}^{∙ ∙}$ . As only nitrogen has a lone pair, it reacts with haloalkanes to form isocyanides.

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