JEE Main 2023 · 24 January · morning · Single correct · +4 / −1
Assertion A : Hydrolysis of an alkyl chloride is a slow reaction but in the presence of NaI, the rate of the hydrolysis increases.
Reason R : I⁻ is a good nucleophile as well as a good leaving group.
In the light of the above statements, choose the correct answer from the options given below
- (a) A is true but R is false
- (b) A is false but R is true
- (c) Both A and R are true and R is the correct explanation of A
- (d) Both A and R are true but R is NOT the correct explanation of A
Answer and solution
Answer (c) Both A and R are true and R is the correct explanation of A
Solution
Chemistry ma’am · 5 steps
Iodide plays both roles here: it swaps in for chloride fast, then leaves even faster when water attacks.
- Why it is slow. Cl⁻ is only a moderate leaving group, and water is a weak nucleophile. So the direct reaction R-Cl + H₂O → R-OH + HCl crawls.
- Iodide steps in. I⁻ is large and highly polarisable, so it is a strong nucleophile. It displaces chloride quickly: R-Cl + I⁻ → R-I + Cl⁻.
- Iodide leaves. The C-I bond is the weakest carbon–halogen bond, and I⁻ is a very stable, weak base. So water now replaces iodide easily: R-I + H₂O → R-OH + H⁺ + I⁻.
- Catalyst returned. I⁻ comes back unchanged at the end, so a small amount of NaI keeps speeding up the hydrolysis. Both of its properties are used, one in each step.
- So. A is true, R is true, and R is exactly why A happens. The answer is (c).
The idea to keep. An ion that is both a good nucleophile and a good leaving group can act as a catalyst: it goes in fast, comes out fast, and is returned unchanged.
Answer from the NTA final answer key. Solution by PrepWiser.