JEE Main 2024 · 1 February · morning · Single correct · +4 / −1
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R) .
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 :
- (a) (A) is correct but (R) is not correct
- (b) Both (A) and (R) are correct and (R) is the correct explanation of (A)
- (c) (A) is not correct but (R) is correct
- (d) Both (A) and (R) are correct but (R) is not the correct explanation of (A)
Answer and solution
Answer (a) (A) is correct but (R) is not correct
Solution
Chemistry ma’am · 3 steps
Ask how the cyanide is held: KCN lets it go free, AgCN keeps carbon tied to silver.
- Two ends of cyanide. The cyanide ion CN⁻ is ambident: it can attack through carbon or through nitrogen. Attack through C gives an alkyl cyanide R-CN, and attack through N gives an isocyanide R-NC.
Reagent Bonding Atom that attacks Main product KCN ionic, free CN⁻ ions C, the more nucleophilic end alkyl cyanide R-CN AgCN mainly covalent, Ag-C bond N, the only free end isocyanide R-NC - Check each statement. The products in (A) are right, so (A) is correct. But AgCN is largely covalent, not highly ionic, so (R) is wrong. That covalent character is exactly why it gives isocyanide.
- So. (A) is correct and (R) is not correct. The answer is (a).
The idea to keep. With an ambident nucleophile, look at how it is bonded. Ionic salts like KCN and NaNO₂ attack through C or O. Covalent silver salts like AgCN and AgNO₂ attack through N.
Answer from the NTA final answer key. Solution by PrepWiser.