1-iodobutane (an alkyl iodide) undergoes SN2 reaction faster than 1-chlorobutane (an alkyl chloride).

Question

Given below are two statements:

one labelled Assertion (A) and the other Reason (R).

Assertion (A): 1-iodobutane (an alkyl iodide) undergoes SN2 reaction faster than 1-chlorobutane (an alkyl chloride).

Reason (R): Iodine is a better leaving group because of its large size. In the light of the above statements, choose the correct answer from the options given below:

1. A. Both A and R are true and R is the correct explanation of A (Correct answer)
2. B. Both A and R are true but R is NOT the correct explanation of A
3. C. A is true but R is false
4. D. A is false but R is true

Correct Answer

Option A — Both A and R are true and R is the correct explanation of A

Detailed Solution & Explanation

The correct answer is Both A and R are true and R is the correct explanation of A.

Key Points

• In an S$_N$2 reaction the rate depends strongly on how good the leaving group is.
• Iodide (I$^-$) is a better leaving group than chloride because the larger, more polarisable iodide ion stabilises the negative charge and the C-I bond is weaker.
• Hence the alkyl iodide reacts faster, and the Reason correctly explains the Assertion.