Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): I$^-$ undergoes SN$_2$ reaction faster than Cl$^-$.
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:

• A. Both A and R are true but R is not the correct explanation of A.
• B. A is true but R is false.
• C. A is false but R is true.
• D. Both A and R are true and R is the correct explanation of A.

Hint:

In SN\(_2\) reactions, the leaving group ability increases with the size of the atom, as larger atoms can stabilize the negative charge better after departure. This is why I\(^-\) is a better leaving group than Cl\(^-\).

Answer 1

The Correct Option is D

- Assertion (A): The rate of SN\(_2\) reactions is greater for I\(^-\) than for Cl\(^-\). This is attributed to I\(^-\)'s larger ionic radius and more dispersed electron cloud, enhancing its nucleophilicity and leaving group ability in SN\(_2\) reactions.
- Reason (R): Iodine serves as a superior leaving group compared to chlorine. This superiority stems from its larger atomic size, which enables it to better stabilize the negative charge upon dissociation from the carbon atom. The increased size facilitates the accommodation of electron density, thus improving its leaving group characteristics.
Conclusion: Both the assertion and the reason are factually correct, and the reason provides a valid explanation for the assertion.
Therefore, option (4) is correct: Both A and R are true, and R is the correct explanation of A.