Question

Which among the following is NOT a feature of \(\text{SN}^2\) mechanism ?

• A. Single step mechanism
• B. Backside attack of nucleophile
• C. Formation of planar carbocation intermediate
• D. Involves simultaneous bond breaking and bond forming

Hint:

SN2 is a one-step concerted process with no carbocation intermediate.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
In the \(\text{S}_\text{N}2\) (bimolecular nucleophilic substitution) mechanism the nucleophile attacks the carbon at the same moment that the leaving group departs.

Step 2: Features of SN2:
It is a single-step mechanism. The nucleophile attacks from the side opposite to the leaving group (backside attack). Bond formation and bond breaking occur simultaneously through a pentacoordinate transition state, and the configuration is inverted.

Step 3: Detailed Explanation:
Formation of a planar carbocation intermediate belongs to the \(\text{S}_\text{N}1\) mechanism, which is a two-step process. In \(\text{S}_\text{N}2\) no carbocation is formed, so option (C) is not a feature of it.

Step 4: Why the other options are wrong.
(A), (B) and (D) are all genuine features of \(\text{S}_\text{N}2\): single step, backside attack and simultaneous bond making and breaking.

Final Answer:
Planar carbocation formation is not an SN2 feature, option (C). \[ \boxed{\text{(C)}} \]