Aldehyde, ketone, acid and acid derivatives contain `gtC=O` group. Aldehyde and ketones gives nucleop addition reactions where as acid and acid derivatives gives nucleophilic addition followed by ellmination reaction Nucleophilic addition reactions followed by ellimination of acid derivatives is known as acyl substitution reacts This subsitution reaction takes places by formation of tertrahedral intermediate.
Which of the following compounds has very poor leaving group?

Options

A.
B.
C.
D.

Answer

To determine which of the compounds has a very poor leaving group, we need to analyze the nature of the leaving groups in the given options.

### Step-by-Step Solution:

1. **Understanding the Reaction Mechanism**:
- Aldehydes and ketones undergo nucleophilic addition where a nucleophile attacks the electrophilic carbon of the carbonyl group (C=O).
- In the case of acid derivatives, the reaction involves nucleophilic addition followed by elimination, leading to acyl substitution.

2. **Identifying the Leaving Group**:
- The leaving group is the part of the molecule that departs during the reaction. The stability of the leaving group after it departs is crucial in determining its effectiveness.
- Generally, a good leaving group is one that can stabilize the negative charge formed after leaving.

3. **Evaluating the Options**:
- **Option A**: C=O with H as the leaving group. When H leaves, it forms H⁻, which is highly unstable and thus a very poor leaving group.
- **Option B**: C=O with Cl as the leaving group. Chlorine (Cl⁻) is a stable ion and a good leaving group.
- **Option C**: C=O with OH as the leaving group. Hydroxide (OH⁻) can also stabilize the negative charge, making it a decent leaving group.
- **Option D**: C=O with OR as the leaving group. Alkoxide ions (OR⁻) are also relatively stable and can act as good leaving groups.

4. **Conclusion**:
- Among the options, the compound with H as the leaving group (Option A) is the one with a very poor leaving group due to the instability of H⁻.

### Final Answer:
The compound with a very poor leaving group is **Option A** (C=O with H as the leaving group).