2021 P1 Q17 - Electrophilic Substitution of Methylbenzene

Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 17.

2021 p1 q17 question

We are required to determine the main reaction involving methylbenzene with bromine chloride.

First let us identify the functional groups present in methylbenzene and their reactions.

2021 p1 q17 functional groups in methylbenzene

alkane - free radical substitution
benzene - electrophilic substitution

The conditions of the reaction were also given.

2021 p1 q17 absence of sunlight

Due to the absence of sunlight, there will be no free radical substitution of alkane since UV light is needed for the initiation step.

Due to the presence of an iron-containing catalyst, there will be electrophilic substitution of benzene.

Hence we can eliminate options A and B where there is substitution into the methyl side chain.

2021 p1 q17 eliminate FRS

Next we need to decide which halogen will be substituted into the benzene ring by determining the electrophile.

2021 p1 q17 deduce electrophile

Bromine is less electronegative than chlorine, hence bromine will be partial positively charged in BrCl.

This makes bromine the electrophile since electrophiles are electron deficient.

Therefore only bromine can be substituted into benzene and option C has to be the answer.

2021 p1 q17 answer

Topic: Arenes, Organic Chemistry, A Level Chemistry, Singapore

Back to list of questions for 2021 A Level H2 Chemistry Paper 1.

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