Which of the following is not a cumulated diene?

Options

A. Hexa-1,2-diene
B. Hexa-2,3-diene
C. Penta-2,3-diene
D. Penta-1,3-diene

Explanation

To determine which of the following is not a cumulated diene, we first need to understand what a cumulated diene is. A cumulated diene is a compound that has two double bonds connected to the same carbon atom.

Let's analyze each option step by step:

1. **Hexa-1,2-diene**:
- This compound has the structure:
```
H2C=CH-CH2-CH2-CH2-CH=CH2
```
- In this structure, the first carbon (C1) has a double bond with C2, and C2 also has a double bond with C1. Therefore, this compound has two double bonds connected to the same carbon atom (C1 and C2).
- **Conclusion**: Hexa-1,2-diene is a cumulated diene.

2. **Hexa-2,3-diene**:
- This compound has the structure:
```
H2C-CH=CH-CH2-CH2-CH=CH2
```
- Here, C2 has a double bond with C3, and C3 has a double bond with C2. Thus, C2 and C3 are connected by two double bonds.
- **Conclusion**: Hexa-2,3-diene is also a cumulated diene.

3. **Penta-2,3-diene**:
- This compound has the structure:
```
H2C-CH=CH-CH=CH2
```
- In this case, C2 has a double bond with C3, and C3 has a double bond with C4. However, no single carbon atom has two double bonds directly attached to it.
- **Conclusion**: Penta-2,3-diene is a cumulated diene.

4. **Penta-1,3-diene**:
- This compound has the structure:
```
H2C=CH-CH2-CH=CH2
```
- In this structure, C1 has a double bond with C2, and C3 has a double bond with C4. No single carbon atom has two double bonds. This is a conjugated diene, where the double bonds are separated by a single bond.
- **Conclusion**: Penta-1,3-diene is not a cumulated diene.

**Final Answer**: Penta-1,3-diene is not a cumulated diene.