Which of the following is anti`-` aromatic in nature ?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is anti-aromatic in nature, we need to follow these steps:

### Step 1: Understand the Criteria for Anti-aromaticity
Anti-aromatic compounds are characterized by:
- Having a cyclic structure.
- Being planar or nearly planar to allow for delocalization of π electrons.
- Following Hückel's rule for anti-aromaticity, which states that they must have 4n π electrons (where n is a non-negative integer).

### Step 2: Analyze Each Compound
We will analyze each of the given structures to check if they meet the criteria for anti-aromaticity.

1. **First Structure (Cyclopropene)**:
- Cyclopropene has 4 π electrons.
- It is cyclic and can be planar.
- Since it has 4 π electrons, it fits the 4n rule (where n=1).
- Therefore, this compound is anti-aromatic.

2. **Second Structure**:
- This structure has 4 π electrons and has delocalization.
- It is also cyclic and can be planar.
- Thus, it satisfies the criteria for anti-aromaticity.

3. **Third Structure (10-annulene)**:
- 10-annulene has 10 π electrons.
- Although it is cyclic, it is not planar due to steric hindrance from the hydrogen atoms.
- Therefore, it does not meet the criteria for anti-aromaticity and is classified as non-aromatic.

4. **Fourth Structure**:
- This structure is also cyclic but does not have the required π electrons for anti-aromaticity.
- It does not meet the criteria and is classified as non-aromatic.

### Step 3: Conclusion
After analyzing all the structures, the second structure is identified as anti-aromatic because it has 4 π electrons and meets the criteria for anti-aromaticity.

### Final Answer:
The compound that is anti-aromatic in nature is **option B**.

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