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 one of the following is least reactive compound for nucleophilic acyl substitution.

Options

A.
B.
C.
D.

Answer

To determine which compound is the least reactive for nucleophilic acyl substitution, we need to analyze the effects of different substituents on the carbonyl carbon's electrophilicity. The reactivity of these compounds depends on the electron-donating or withdrawing nature of the groups attached to the carbonyl carbon.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Acyl Substitution**:
- Nucleophilic acyl substitution involves the addition of a nucleophile to the carbonyl carbon, forming a tetrahedral intermediate, followed by elimination of a leaving group.
- The reactivity of the carbonyl compound is influenced by the nature of the substituents attached to the carbonyl carbon.

2. **Analyzing the Options**:
- We need to evaluate each option based on how the substituents affect the positive charge on the carbonyl carbon.

3. **Option A**: CH3-C(=O)-Cl
- The methyl group (CH3) is an electron-donating group (through +I effect), which decreases the positive charge on the carbonyl carbon, making it less reactive.

4. **Option B**: CH3-C(=O)-NH-CH3
- The NH group is a +R group, which also donates electrons to the carbonyl carbon, further decreasing its positive charge. This makes it even less reactive than option A.

5. **Option C**: CH3-C(=O)-NH-C6H5
- The NH group is still present, but now it is connected to a phenyl ring (C6H5). The resonance effect of the benzene ring can stabilize the carbonyl carbon but also allows for some electron donation, making it more reactive than option B.

6. **Option D**: CH3-C(=O)-NH-C6H5(NO2)
- The presence of the nitro group (NO2) on the benzene ring is an electron-withdrawing group (-R effect). This increases the positive charge on the carbonyl carbon, making it more reactive compared to the previous options.

7. **Conclusion**:
- Comparing the effects of the substituents, we find that option B (CH3-C(=O)-NH-CH3) has the least positive charge on the carbonyl carbon due to the electron-donating effects of both the methyl and the amine groups. Therefore, it is the least reactive compound for nucleophilic acyl substitution.

### Final Answer:
**Option B: CH3-C(=O)-NH-CH3 is the least reactive compound for nucleophilic acyl substitution.**