Which of the following is a `beta`-elimination reaction ?

Options

A.
B. (2) `CHCl_3 + KOH overset(Delta)to C Cl_3`
C.
D.

Explanation

To determine which of the given reactions is a beta-elimination reaction, we need to understand the definition of a beta-elimination reaction. A beta-elimination reaction involves the removal of two atoms or groups from adjacent carbon atoms in a substrate molecule.

### Step-by-Step Solution:

1. **Understanding Beta-Elimination**:
- In a beta-elimination reaction, two atoms or groups are removed from adjacent carbon atoms (C1 and C2). This process typically leads to the formation of a double bond between these two carbon atoms.

2. **Analyzing the First Reaction**:
- In the first reaction, we have a substrate that reacts with sodium hydroxide to form a three-membered ring.
- The atoms eliminated are bromine (Br) from carbon 1 and a hydrogen atom from an oxygen (not from carbon 2).
- Since the hydrogen is not from the adjacent carbon (C2), this reaction does not qualify as a beta-elimination reaction.

3. **Analyzing the Second Reaction**:
- The second reaction involves CHCl3 reacting with a base, resulting in the formation of CCl3.
- Here, only hydrogen is eliminated, and there is no elimination from adjacent carbon atoms. Thus, this is also not a beta-elimination reaction.

4. **Analyzing the Third Reaction**:
- In the third reaction, a substrate reacts with a hydroxyl radical to form a cyclic compound.
- In this case, bromine is eliminated from one carbon and hydrogen from another carbon, but they are not adjacent (1,3 elimination). Therefore, this is not a beta-elimination reaction.

5. **Analyzing the Fourth Reaction**:
- In the fourth reaction, chlorine (Cl) is eliminated from carbon 1 and hydrogen from carbon 2.
- Here, we see that both atoms are eliminated from adjacent carbon atoms (C1 and C2), which fits the definition of a beta-elimination reaction.

6. **Conclusion**:
- Based on the analysis, the fourth reaction is the only one that qualifies as a beta-elimination reaction.

### Final Answer:
The fourth reaction is a beta-elimination reaction.

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