Which of the following reactions(s) is/are sterospecific but non-steroselcetive?

Options

A. `SN^(2)`
B. `E1`
C. `E2`
D. `ElcB`

Explanation

To determine which of the following reactions are stereospecific but not stereoselective, we will analyze the reactions: SN2, E1, E2, and E1CV.

### Step-by-Step Solution:

1. **Understanding Stereospecificity and Stereoselectivity**:
- **Stereospecificity**: A reaction is stereospecific if the configuration of the starting material determines the configuration of the product. This means that a specific stereoisomer of the reactant will lead to a specific stereoisomer of the product.
- **Stereoselectivity**: A reaction is stereoselective if it preferentially forms one stereoisomer over another from a mixture of stereoisomers.

2. **Analyzing SN2 Reaction**:
- The SN2 reaction is stereospecific because it involves a backside attack on the substrate, leading to inversion of configuration. However, it is also stereoselective because it selectively forms one stereoisomer from a chiral substrate.
- **Conclusion**: SN2 is not the answer.

3. **Analyzing E1 Reaction**:
- The E1 reaction involves the formation of a carbocation intermediate. While the formation of the carbocation is specific, the elimination step can lead to a mixture of products (both E and Z isomers).
- **Conclusion**: E1 is not stereospecific as it does not lead to a specific stereoisomer.

4. **Analyzing E2 Reaction**:
- The E2 reaction is stereospecific because it requires anti-periplanar geometry for the elimination to occur. However, it can also lead to the formation of multiple stereoisomers depending on the substrate and the elimination pathway.
- **Conclusion**: E2 is not the answer as it is also stereoselective.

5. **Analyzing E1CV Reaction**:
- The E1CV (Elimination Unimolecular Conjugate Base) reaction is stereospecific because the initial step involves the loss of a beta-hydrogen to form a specific carbocation. However, the subsequent steps can lead to a mixture of products, including different stereoisomers (enantiomers or diastereomers).
- **Conclusion**: E1CV is stereospecific but not stereoselective.

### Final Answer:
The reaction that is stereospecific but not stereoselective is **E1CV**.