Compare Electrophilic Substitution with Different Substituents

In this JC2 webinar let's compare the reactivity of electrophilic substitution of benzene, methylbenzene and phenol.

1. Bromination

The reagents and conditions are as follows:

Benzene: Br2 in FeBr3 catalyst
Methylbenzene: Br2 in FeBr3 catalyst
Phenol: Br2 in CCl4 solvent

compare ES with different substituents bromination

Notice methyl group is a typical activating group which should make benzene more reactive, but the reagents and conditions remain the same as compared to benzene.

Phenol is much more reactive in terms of electrophilic substitution as -OH is a highly activating group and makes benzene very electron rich and attractive to electrophiles.

2. Nitration

The reagents and conditions are as follows:

Benzene: conc HNO3 in conc H2SO4 catalyst, 50 to 60oC
Methylbenzene: conc HNO3 in conc H2SO4 catalyst, 30oC
Phenol: dilute HNO3 at 20oC

compare ES with different substituents nitration

Activating methyl group will make benzene slightly more reactive so a lower temperature is required, but we still need concentrated HNO3 and catalyst.

For phenol the reagents and conditions are significantly different. Catalyst is not required and the reaction can be done at cold conditions.

By comparing the reagents and conditions required for different activating groups, we can better remember these electrophilic substitution reactions of benzene as we treat them as a bundle.

This comparison approach is useful in Organic Chemistry as there are many functional groups that undergo similar reactions such as oxidation, reduction, neutralisation and hydrolysis.

Topic: Hydroxy Compounds & Arenes, Organic Chemistry, A Level Chemistry, Singapore

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