Electrophilic Substitution of Methylbenzene vs. Electrophilic Substitution of Nitrobenzene

Attribute	Electrophilic Substitution of Methylbenzene	Electrophilic Substitution of Nitrobenzene
Starting Material	Methylbenzene (toluene)	Nitrobenzene
Electrophile	Electrophile attacks the benzene ring	Electrophile attacks the benzene ring
Activating/Deactivating Group	Methyl group is activating	Nitro group is deactivating
Reaction Rate	Reaction is faster due to activating group	Reaction is slower due to deactivating group
Major Product	Ortho and para substitution products	Meta substitution product

Introduction

Electrophilic substitution is a common reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. Methylbenzene, also known as toluene, and nitrobenzene are two aromatic compounds that undergo electrophilic substitution reactions. In this article, we will compare the attributes of electrophilic substitution of methylbenzene and nitrobenzene.

Electrophilic Substitution of Methylbenzene

Methylbenzene is a derivative of benzene with a methyl group attached to the benzene ring. When methylbenzene undergoes electrophilic substitution, the methyl group is considered to be an activating group. This means that it increases the electron density on the benzene ring, making it more reactive towards electrophiles. The methyl group donates electron density through the inductive effect and the hyperconjugation effect, making the benzene ring more nucleophilic.

One of the most common electrophilic substitution reactions of methylbenzene is the nitration reaction, where nitric acid and sulfuric acid are used to introduce a nitro group onto the benzene ring. The presence of the methyl group activates the benzene ring towards electrophilic attack, leading to a faster reaction compared to benzene itself. The product of the nitration reaction is methyl nitrobenzene.

Another important electrophilic substitution reaction of methylbenzene is the Friedel-Crafts acylation reaction, where an acyl group is introduced onto the benzene ring. The presence of the methyl group activates the benzene ring towards electrophilic attack, allowing for the acylation reaction to proceed smoothly. The product of the acylation reaction is methyl phenyl ketone.

In summary, the presence of the methyl group in methylbenzene activates the benzene ring towards electrophilic substitution reactions, making it more reactive compared to benzene itself.

Electrophilic Substitution of Nitrobenzene

Nitrobenzene is a derivative of benzene with a nitro group attached to the benzene ring. When nitrobenzene undergoes electrophilic substitution, the nitro group is considered to be a deactivating group. This means that it decreases the electron density on the benzene ring, making it less reactive towards electrophiles. The nitro group withdraws electron density through the resonance effect, making the benzene ring less nucleophilic.

One of the most common electrophilic substitution reactions of nitrobenzene is the halogenation reaction, where a halogen such as chlorine or bromine is introduced onto the benzene ring. The presence of the nitro group deactivates the benzene ring towards electrophilic attack, leading to a slower reaction compared to benzene itself. The product of the halogenation reaction is halonitrobenzene.

Another important electrophilic substitution reaction of nitrobenzene is the sulfonation reaction, where sulfuric acid is used to introduce a sulfonic acid group onto the benzene ring. The presence of the nitro group deactivates the benzene ring towards electrophilic attack, making the sulfonation reaction less favorable compared to benzene itself. The product of the sulfonation reaction is nitrobenzene sulfonic acid.

In summary, the presence of the nitro group in nitrobenzene deactivates the benzene ring towards electrophilic substitution reactions, making it less reactive compared to benzene itself.

Comparison of Attributes

• Methylbenzene has an activating group (methyl group) that increases the reactivity of the benzene ring towards electrophiles, while nitrobenzene has a deactivating group (nitro group) that decreases the reactivity of the benzene ring.
• Electrophilic substitution reactions of methylbenzene are faster and more favorable compared to benzene itself, while electrophilic substitution reactions of nitrobenzene are slower and less favorable compared to benzene.
• Methylbenzene is more prone to undergo electrophilic substitution reactions due to the electron-donating nature of the methyl group, while nitrobenzene is less prone to undergo such reactions due to the electron-withdrawing nature of the nitro group.