Which of the following structure will not have `4pi` electrons

Options

A.
B.
C.
D.

Explanation

To determine which of the provided structures does not have 4 pi electrons, we need to analyze each structure in terms of the number of pi bonds and the electrons associated with them. Here is a step-by-step solution:

### Step 1: Understand Pi Electrons
- Pi electrons are those that are involved in pi bond formation. Each pi bond consists of 2 electrons.

### Step 2: Analyze Each Structure
1. **Structure A**:
- Contains one pi bond between two carbon atoms.
- Additionally, there is a negative charge on one of the carbons, which contributes 2 extra electrons.
- Total: 2 (from the pi bond) + 2 (from the negative charge) = **4 pi electrons**.

2. **Structure B**:
- Contains two pi bonds.
- Each pi bond contributes 2 electrons.
- Total: 2 (from the first pi bond) + 2 (from the second pi bond) = **4 pi electrons**.

3. **Structure C**:
- Contains a positive charge, indicating a carbocation.
- A carbocation has an empty p orbital and does not contribute any pi electrons.
- However, it has two pi bonds, which contribute 4 electrons.
- Total: 4 (from the two pi bonds) = **4 pi electrons**.

4. **Structure D**:
- Contains three pi bonds.
- Each pi bond contributes 2 electrons.
- Total: 2 (from the first pi bond) + 2 (from the second pi bond) + 2 (from the third pi bond) = 6 pi electrons.
- Additionally, there are 2 electrons from a negative charge involved in resonance.
- Total: 6 + 2 = **8 pi electrons**.

### Step 3: Conclusion
- Structures A, B, and C all have 4 pi electrons.
- Structure D does not have 4 pi electrons; it has 8 pi electrons.

Thus, the structure that does not have 4 pi electrons is **Structure D**.