Question

Least reactive alkyl chloride in an \( S_N2 \) reaction is:

• A. 1-Chloro butane
• B. 1-Chloro 2-Methyl propane
• C. 2-Chloro 2-Methyl propane
• D. 2-Chloro butane

Hint:

SN2 reactivity decreases as steric hindrance near the electrophilic carbon increases. Tertiary halides are typically unreactive in SN2.

Answer 1

The Correct Option is C

The \( S_N2 \) mechanism proceeds via a backside attack by the nucleophile, and is **highly sensitive to steric hindrance**. - In **1° alkyl halides** (like 1-chloro butane), the carbon bonded to the halogen is less hindered, so reaction proceeds faster. - **2° alkyl halides** (like 2-chloro butane) have moderate steric hindrance. - **Tertiary (3°)** alkyl halides, such as **2-chloro 2-methyl propane**, are **extremely hindered** due to bulky alkyl groups around the carbon. This blocks the backside approach and makes SN2 almost impossible. Hence, **2-chloro 2-methyl propane** is the **least reactive** toward SN2.