A2 Chem - Benzene and Methlybenzene - Reactivity

Can someone explain to me why benzene needs a higher temperature than Methlybenzene when reacting some mechnisms/explain to me the difference in reactivity between methylbenzene and benzene...

Thanks! :smile:

OP

anyone? Bumpz.

explanation straight out of notes:
Methylbenzene is more reactive than benzene because the methyl increases the electron density of the pi ring orbital by induction.

The methyl group alters the electron density of each carbon atom so that the 2,4 and 6 positions have the max density and the 3 and 5 positions have min density. Therefore, electrophilic substituion reactions of methylbenzene produce two monosubstitued isomers, i.e 1,4 and 1,2

You can usually consider that alkyl groups are +I (positive electron inducing) i.e. that they are relatively positive comparted to the other groups to which they are attached as other groups can pull electron density from them.

A methyl group, then, can be thought to 'push' electrons into the benzene ring, increasing its electron density. As the normal reaction of the benzene ring is electrophilic substitution this makes the ring more reactive (the ring has a relatively greater electron density than a benzene ring without substituents)

As AMH189 says, this also confers directional characteristics on the ring, in this case 2,4,6, directing.

Reply 4

arsenalfan.

OP

1

thanks for all your help.

Reply 5

A Y A Z

11

Methylbenzene has an alkyl group; any compound with an alkyl group is more stable, as the alkyl group tends to 'donate' electrons (the move towards the) to the positively charged Carbon atom.

This is an important property of alkyl groups. Remember it.

For the same reason, in reaction mechanisms, the carbo cation surrounded by more number of alkyl groups is more stable, and thus forms the greater percentage of the product.

A Y Z

Methylbenzene has an alkyl group; any compound with an alkyl group is more stable, as the alkyl group tends to 'donate' electrons (the move towards the) to the positively charged Carbon atom.

This is an important property of alkyl groups. Remember it.

For the same reason, in reaction mechanisms, the carbo cation surrounded by more number of alkyl groups is more stable, and thus forms the greater percentage of the product.

'fraid you cannot apply this argument as, while it is true for aliphatic compounds, the same argument does not apply to benzene rings with methyl substituents. They increase the electron density of the ring making the ring MORE reactive (and hence the compound less stable thermodynamically)

Reply 7

A Y A Z

11

Like I said, this is just am important property of alkyl groups, not a specific answer for the question.

That had already been answered :smile:

Reply 8

ChemClues

i agree with majority

The methyl group on the benzene ring has a positive inductive effect, essentially the e- in the methyl group get pushed closer to the benzene ring increasing the e- density about the ring and thus increasing its reactivity and its ability to donate e- to form new bonds, the longer the chain the greater the inductive effect will be, this theory is most associated with amines.

Reply 9

cpchem

14

There is hardly any difference between the inductive contribution of a methyl group or a higher alkyl substituent, as far as I can think...

A2 Chem - Benzene and Methlybenzene - Reactivity

Related discussions

Latest

Trending

Trending

Articles for you