The electrophile, `E^((o+))` attacks the benzene ring to generate the intermediate `sigma`-complex. Of the following which `sigma`-complex is of lowest energy?

Options

A.
B.
C.
D.

Explanation

To determine which sigma-complex is of lowest energy among the given options, we need to analyze the stability of the sigma-complexes formed when an electrophile attacks the benzene ring. Here’s a step-by-step solution:

### Step 1: Understand the Formation of Sigma-Complex
When an electrophile (E⁺) attacks the benzene ring, it disrupts the aromaticity of the benzene and forms a sigma-complex (also known as an arenium ion). The positive charge in the sigma-complex can be stabilized by resonance.

### Step 2: Identify the Influence of Substituents
The stability of the sigma-complex is influenced by the nature of the substituents on the benzene ring:
- **Electron-withdrawing groups (EWGs)**, such as NO₂, decrease the stability of the sigma-complex by pulling electron density away from the ring, increasing the positive charge density on the carbon where the electrophile is attached.
- **Electron-donating groups (EDGs)**, such as alkyl groups, increase the stability of the sigma-complex by donating electron density to the ring, thus reducing the positive charge density.

### Step 3: Analyze the Given Sigma-Complexes
Assuming we have four sigma-complexes labeled A, B, C, and D:
- **Complexes A, C, and D** contain the NO₂ group, which is an electron-withdrawing group. This destabilizes the sigma-complex due to increased positive charge density.
- **Complex B** does not have any electron-withdrawing groups and is therefore more stable.

### Step 4: Conclusion on Stability
Since Complex B lacks destabilizing substituents, it will be the most stable among the options provided. Therefore, it will have the lowest energy.

### Final Answer
The sigma-complex of lowest energy is **B**.