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

Options

A. `SN^(1)`
B. `E1`
C. `E2`
D. `ElcB`

Explanation

To determine which of the reactions are both non-stereospecific but stereoselective, let's analyze each reaction type mentioned in the question: SN1, E1, E2, and E1CB.

### Step-by-Step Solution:

1. **Understanding Stereospecificity and Stereoselectivity**:
- **Stereospecific** reactions yield a specific stereoisomer from a specific reactant stereoisomer.
- **Stereoselective** reactions preferentially form one stereoisomer over others, but do not necessarily require a specific starting stereoisomer.

2. **Analyzing SN1 Reaction**:
- The SN1 reaction involves the formation of a carbocation intermediate after the leaving group departs.
- The nucleophile can attack from either side of the planar carbocation, leading to a mixture of stereoisomers.
- Therefore, SN1 is **non-stereospecific** but not stereoselective as it does not favor the formation of one stereoisomer over another.

3. **Analyzing E1 Reaction**:
- The E1 reaction also involves the formation of a carbocation intermediate.
- After the formation of the carbocation, a base abstracts a beta-hydrogen, leading to the formation of a double bond.
- The carbocation can rearrange, and the base can abstract a hydrogen from either side of the carbocation, leading to different products.
- However, typically, one product is favored due to stability (for example, the more substituted alkene). Thus, E1 is **non-stereospecific** but **stereoselective**.

4. **Analyzing E2 Reaction**:
- The E2 reaction is a concerted mechanism where the base abstracts a beta-hydrogen while the leaving group departs.
- This reaction is stereospecific because the orientation of the hydrogen abstraction and leaving group must be anti-periplanar for the reaction to occur.
- Therefore, E2 is **stereospecific**.

5. **Analyzing E1CB Reaction**:
- The E1CB mechanism involves the formation of a carbanion intermediate, which can lead to the formation of a double bond.
- Similar to E1, the reaction can lead to different products, but it does not favor a specific stereoisomer.
- However, it is not typically classified as stereoselective since it does not preferentially form one stereoisomer over another.

### Conclusion:
Based on the analysis, the only reaction that is both **non-stereospecific** and **stereoselective** is the **E1 reaction**.

### Final Answer:
**E1 reaction is both non-stereospecific and stereoselective.**

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