Which of the following is strongest `-m` group

Options

A. `-SO_(3)H`
B. `-COOH`
C. `-NO_(2)`
D. `-C-=N`

Answer

To determine which of the given groups is the strongest -M (minus mesomeric) group, we need to analyze the electron-withdrawing effects of each group. The -M effect refers to the ability of a substituent to withdraw electron density through resonance.

### Step-by-Step Solution:

1. **Understanding the -M Effect**:
- The -M effect is a resonance effect where a substituent withdraws electron density from a conjugated system. This effect is typically seen in groups that have a lone pair of electrons or pi bonds that can delocalize into the system.

2. **Identifying the Groups**:
- The groups provided in the question are:
- SO3H (sulfonic acid)
- COH (aldehyde)
- NO2 (nitro group)
- C≡N (nitrile)

3. **Ranking the Groups Based on -M Effect**:
- The strength of the -M effect can be ranked based on the ability of the groups to withdraw electrons:
- **NO2 (Nitro group)**: This group is known to be a very strong electron-withdrawing group due to the presence of electronegative oxygen atoms and the resonance structure it can form.
- **C≡N (Nitrile)**: This group is also a strong electron-withdrawing group, but not as strong as NO2.
- **SO3H (Sulfonic acid)**: This group has a significant -M effect but is generally weaker than NO2 and C≡N.
- **COH (Aldehyde)**: This group has a weaker -M effect compared to the others listed.

4. **Conclusion**:
- Based on the analysis, the group with the strongest -M effect is **NO2**. Therefore, the answer to the question is **NO2**.

### Final Answer:
The strongest -M group among the given options is **NO2**.

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