Question Video: Identifying the Reaction That Is Not a Substitution Reaction of Benzene | Nagwa Question Video: Identifying the Reaction That Is Not a Substitution Reaction of Benzene | Nagwa

Question Video: Identifying the Reaction That Is Not a Substitution Reaction of Benzene Chemistry • Third Year of Secondary School

Which of the following reactions is not a substitution reaction of benzene? [A] Conversion of benzene to hexachlorocyclohexane [B] Conversion of benzene to nitrobenzene [C] Conversion of benzene to chlorobenzene [D] Conversion of benzene to toluene [E] Conversion of benzene to benzenesulfonic acid

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Video Transcript

Which of the following reactions is not a substitution reaction of benzene? (A) Conversion of benzene to hexachlorocyclohexane. (B) Conversion of benzene to nitrobenzene. (C) Conversion of benzene to chlorobenzene. (D) Conversion of benzene to toluene. (E) Conversion of benzene to benzenesulfonic acid.

A substitution reaction is a type of reaction where parts of a molecule are removed and replaced with other functional groups. When benzene undergoes a substitution reaction, one or more hydrogen atoms are removed and replaced with other functional groups.

Let’s begin by looking at answer choice (B). During the conversion of benzene to nitrobenzene, a hydrogen atom on the benzene ring is replaced with a nitro or NO2 group. This type of reaction is known as a nitro substitution reaction or, more simply, nitration. Since we are looking for a reaction that is not a substitution reaction, we can eliminate answer choice (B).

Now let’s take a look at answer choice (C). During the conversion of benzene to chlorobenzene, a hydrogen atom on the benzene ring is replaced with a chlorine atom. This type of reaction is known as a halogen substitution reaction. Because the halogen used here is chlorine, this reaction is also known as chlorination. Since chlorination is a substitution reaction, we can eliminate answer choice (C).

Now let’s look at answer choice (D). During the conversion of benzene to toluene, a hydrogen atom on the benzene ring is replaced with a methyl group. When an alkyl group like a methyl group replaces hydrogen atoms on benzene, the reaction is known as an alkyl substitution or alkylation reaction. Because alkylation is a substitution reaction, we can eliminate answer choice (D).

As for answer choice (E), during the conversion of benzene to benzenesulfonic acid, a hydrogen atom on the benzene ring is replaced with a sulfo or SO3H group. This type of substitution reaction is known as a sulfo substitution or sulfonation reaction. Because sulfonation is a substitution reaction, we can eliminate answer choice (E).

That leaves only answer choice (A). In the conversion of benzene to hexachlorcyclohexane, six chlorine atoms are added to the benzene molecule, but no atoms are removed from benzene. This reaction is not a substitution reaction, but a type of addition reaction known as halogen addition. In a halogen addition reaction, a molecule combines with one or more halogen molecules to form a larger molecule. In the reaction shown, three molecules of the halogen chlorine react with the benzene molecule to form hexachlorocyclohexane and no other product.

In conclusion, the reaction that is not a substitution reaction of benzene is answer choice (A): conversion of benzene to hexachlorocyclohexane.

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