Which of the following Allene is achiral?

Options

A.
B.
C.
D.

Answer

To determine which of the following allenes is achiral, we need to analyze the chirality of each compound based on the structural requirements for chirality.

### Step-by-Step Solution:

1. **Understanding Chirality**:
- Chirality refers to a property of a molecule that makes it non-superimposable on its mirror image. For a carbon atom to be chiral, it must be sp³ hybridized and bonded to four different substituents.

2. **Identifying the Structure of Allenes**:
- Allenes have a cumulated double bond structure (C=C=C). In allenes, the central carbon atom is sp hybridized, while the terminal carbons are sp² hybridized.

3. **Analyzing Each Allene**:
- For each allene, we need to check if there are four different substituents around the sp² hybridized carbon atoms and if there is any symmetry.

4. **Case Analysis**:
- **Allene 1**: If it has two identical substituents on one side (e.g., H and CH₃ on one side, and H and H on the other), it is symmetric and thus achiral.
- **Allene 2**: If it has two identical substituents (e.g., H and H on one side, and C₂H₅ and H on the other), it is also symmetric and thus achiral.
- **Allene 3**: If it has four different substituents (e.g., H, CH₃, C₂H₅, and another different group), it is asymmetric and thus chiral.
- **Allene 4**: If it has two identical substituents (e.g., F and F on one side, and H and H on the other), it is symmetric and thus achiral.

5. **Conclusion**:
- After analyzing the structures, we find that the allenes with identical substituents on one side are achiral. Therefore, the answer to the question is that the achiral allene is the one with symmetry due to identical substituents.

### Final Answer:
The achiral allene is the one that has symmetry due to identical substituents.