Which of the following halides undergo `E_(2)` elimination?

Options

A.
B.
C.
D.

Answer

To determine which of the given halides undergo E2 elimination, we need to understand the mechanism of E2 elimination and the structural requirements for it to occur.

### Step-by-Step Solution:

1. **Understanding E2 Elimination**:
- E2 elimination is a bimolecular elimination reaction where a leaving group (halide) and a hydrogen atom are removed from adjacent carbon atoms, resulting in the formation of a double bond.
- The elimination occurs in an anti-coplanar fashion, meaning that the leaving group and the hydrogen must be on opposite sides (anti) of the molecule.

2. **Identifying the Halides**:
- We need to analyze the structures of the halides provided in the question. Typically, these will be alkyl halides with halogens like Cl, Br, or I attached to them.

3. **Analyzing Each Halide**:
- For each halide, identify the alpha (the carbon attached to the halide) and beta (the adjacent carbon) positions.
- Check if there is a hydrogen atom on the beta carbon that is in the anti position to the halide.

4. **Example Analysis**:
- **Halide 1 (e.g., R-Br)**:
- If there is a hydrogen on the beta carbon that is anti to the bromine (Br), then E2 elimination can occur.
- **Halide 2 (e.g., R-Cl)**:
- Similarly, check if there is a hydrogen on the beta carbon that is anti to the chlorine (Cl).
- **Halide 3 and 4**:
- If the hydrogens on the beta carbon are not in the anti position to the halide, E2 elimination cannot occur.

5. **Conclusion**:
- After analyzing all the halides, we conclude which ones can undergo E2 elimination based on the presence of anti hydrogens relative to the leaving group.

### Final Answer:
- Based on the analysis, the halides that can undergo E2 elimination are **Halide 1 and Halide 2**.