Which of the following staements are correct about `ElcB` reaction ?

Options

A. It proceeds via the formation of carbanion intermediate.
B. Strong `EWG` and poor leaving groups favour the reaction.
C. It is a unimolecular reaction with secound order kinetics.
D. When `D` is incorporated in the staring material by the solvent `EtOD` and the reaction is interupted before completion, no `D` is found either in the substrare or in the product.

Explanation

To determine which statements are correct about the E1CB (Elimination Unimolecular Conjugate Base) reaction, let's analyze the characteristics and steps involved in this reaction mechanism.

### Step-by-Step Solution:

1. **Understand the E1CB Mechanism**:
- The E1CB mechanism involves the formation of a conjugate base as an intermediate. This reaction typically requires a strong base and a poor leaving group.

2. **Identify the Steps in the Reaction**:
- **Step 1**: A strong base abstracts a proton (H⁺) from the beta carbon, leading to the formation of a conjugate base (carbanion).
- **Step 2**: The poor leaving group departs, resulting in the formation of an alkene.

3. **Evaluate the Statements**:
- **Statement A**: "The reaction requires a strong base and a poor leaving group."
- This statement is correct. The E1CB mechanism indeed requires a strong base to remove a proton and a poor leaving group for the reaction to proceed.

- **Statement B**: "Strong electron-withdrawing groups and poor leaving groups favor the reaction."
- This statement is also correct. Electron-withdrawing groups increase the acidity of the hydrogen on the beta carbon, making it easier for the base to abstract it, thus favoring the reaction.

- **Statement C**: "It is a unimolecular reaction."
- This statement is correct as well. The rate-determining step involves only one molecule (the substrate), making it unimolecular.

- **Statement D**: "When deuterium is incorporated in the starting material, no deuterium is found in the substrate or in the product."
- This statement is incorrect. If deuterium is present in the starting material, it can be found in the product as well, assuming the reaction proceeds to completion.

4. **Conclusion**:
- The correct statements about the E1CB reaction are A, B, and C. Statement D is incorrect.

### Final Answer:
The correct statements about the E1CB reaction are:
- A: Correct
- B: Correct
- C: Correct
- D: Incorrect

Thus, the answer is A, B, and C are correct.