Reactivity of Aromatic Compounds towards Electrophilic Substitution Reaction

I. Toluene
II. Benzene
III. Chlorobenzene
IV. Nitrobenzene

Aromatic compounds undergo electrophilic substitution reactions where an electrophile attacks the electron-rich benzene ring and substitutes one of the hydrogen atoms. The reactivity of aromatic compounds towards electrophilic substitution reactions depends on the electron density on the benzene ring, which is influenced by the presence of electron-donating or electron-withdrawing groups.

1. Nitrobenzene (IV)
Nitrobenzene is the most reactive among the given compounds towards electrophilic substitution reactions. The nitro group (-NO2) is a strong electron-withdrawing group, which decreases the electron density on the benzene ring. This makes the benzene ring more susceptible to attack by electrophiles, resulting in a higher reactivity.

2. Chlorobenzene (III)
Chlorobenzene is less reactive compared to nitrobenzene because the chlorine atom is a weak electron-withdrawing group. Although it withdraws electron density from the benzene ring, its effect is not as strong as the nitro group. Hence, chlorobenzene is less reactive towards electrophilic substitution reactions than nitrobenzene.

3. Benzene (II)
Benzene is less reactive than chlorobenzene because it does not contain any electron-withdrawing group. It has a balanced electron density on the benzene ring, which makes it less susceptible to attack by electrophiles. However, benzene can still undergo electrophilic substitution reactions, albeit at a slower rate compared to compounds with stronger electron-withdrawing groups.

4. Toluene (I)
Toluene is the least reactive among the given compounds towards electrophilic substitution reactions. It contains a methyl group (-CH3), which is an electron-donating group. The methyl group increases the electron density on the benzene ring, making it less susceptible to attack by electrophiles. As a result, toluene undergoes electrophilic substitution reactions at a slower rate compared to benzene and other compounds with electron-withdrawing groups.

In summary, the correct order of reactivity towards aromatic electrophilic substitution reactions is:
IV (Nitrobenzene) > III (Chlorobenzene) > II (Benzene) > I (Toluene)