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.
