Out of benzene, m–dinitrobenzene and toluene which will undergo nitration most easily and why?

Explanation

To determine which compound among benzene, m-dinitrobenzene, and toluene undergoes nitration most easily, we need to analyze the electronic effects of the substituents on the benzene ring. Nitration is an electrophilic substitution reaction where an electrophile (the nitronium ion, NO2+) attacks the benzene ring.

### Step-by-step Solution:

1. **Understanding Nitration**:
- Nitration is an electrophilic substitution reaction where the nitronium ion (NO2+) acts as the electrophile. The reaction requires a benzene ring that is electron-rich to facilitate the attack by the electrophile.

2. **Analyzing Benzene**:
- Benzene (C6H6) has no substituents. It is a neutral compound and has a moderate electron density. Therefore, it can undergo nitration, but not as easily as compounds with electron-donating groups.

3. **Analyzing Toluene**:
- Toluene (C6H5CH3) has a methyl group (–CH3) as a substituent. The methyl group is an electron-donating group through the +I (inductive) effect. This increases the electron density on the benzene ring, making it more reactive towards electrophiles like the nitronium ion. Thus, toluene will undergo nitration more easily than benzene.

4. **Analyzing m-Dinitrobenzene**:
- m-Dinitrobenzene (C6H3(NO2)2) has two nitro groups (–NO2) in the meta position. Nitro groups are strong electron-withdrawing groups due to their –M (mesomeric) and –I (inductive) effects. They decrease the electron density on the benzene ring, making it less reactive towards electrophilic substitution. Therefore, m-dinitrobenzene will undergo nitration the least easily among the three compounds.

5. **Comparing Reactivity**:
- Based on the analysis:
- Toluene (most reactive due to electron-donating methyl group)
- Benzene (moderately reactive)
- m-Dinitrobenzene (least reactive due to electron-withdrawing nitro groups)

### Conclusion:
Toluene will undergo nitration most easily, followed by benzene, and then m-dinitrobenzene.