Some meta-directing substituents in aromatic substitution are given which one is the most deactivating?

Options

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

Explanation

To determine which of the given meta-directing substituents is the most deactivating in aromatic substitution, we need to analyze the nature of each substituent and its effect on the electron density of the benzene ring.

### Step-by-Step Solution:

1. **Identify the Groups**: The groups provided are CN (cyano), SO3H (sulfonic acid), COOH (carboxylic acid), and NO2 (nitro).

2. **Understand Deactivating Groups**: Deactivating groups are those that withdraw electron density from the benzene ring. This makes the ring less reactive towards electrophilic substitution.

3. **Electronegativity Consideration**: The strength of the deactivating effect depends on the electronegativity of the atoms in the substituent. The more electronegative the atom, the stronger the electron-withdrawing effect.

4. **Analyze Each Group**:
- **CN (Cyano)**: The carbon in the cyano group is bonded to a nitrogen, which is relatively electronegative, but not as much as oxygen or nitrogen in other groups.
- **SO3H (Sulfonic Acid)**: Sulfur is less electronegative than nitrogen and does withdraw electrons, but not as effectively as a nitro group.
- **COOH (Carboxylic Acid)**: The carbon in the carboxylic acid is also less electronegative than nitrogen.
- **NO2 (Nitro)**: The nitrogen in the nitro group is highly electronegative and is known to be a strong electron-withdrawing group.

5. **Comparison of Effects**: Among the groups analyzed, the NO2 group has the highest electronegativity due to the nitrogen atom, making it the strongest electron-withdrawing group.

6. **Conclusion**: Therefore, the most deactivating group among the given options is **NO2 (Nitro)**.

### Final Answer:
The most deactivating meta-directing substituent is **NO2 (Nitro)**.