Arenes Pop Quiz 2

An electrophile is _____________________________________________.

• a lone pair acceptor.

• an electron pair acceptor.

• a positively charged ion.

• a species with a partial positive charge.

Answer explanation

Note: an electron pair can either be a lone pair OR a bond pair of electrons.

Benzene...

• has sp² carbon atoms

• electrons is delocalised around the ring

• electrons from π orbital are shared only among 2 carbon with double bond

GCE 'A' Level 2017 P3 Q1d(i): When benzene is heated with BrCl in the presence of AlCl₃, a monohalogenobenzene is formed. Which of the following is the monohalogenobenzene formed?

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Answer explanation

Bromine carries a delta + (electron-deficient) as it is less electronegative than chlorine, hence the electrophile generated is Br⁺.

What is the product formed?

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• CH₃Cl

Answer explanation

AlCl₃ reacts with CH₃COCl to generate the electrophile CH₃C⁺O, which attacks the benzene ring (electrophilic substitution).

What is the product formed?

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Answer explanation

Note that Cl⁺ is an electrophile and can take part in both electrophilic addition with the alkene and electrophilic substitution with benzene.

What is the product formed?

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Answer explanation

The more stable carbocation is the secondary carbocation, which acts as the electrophile in electrophilic substitution.

Match the following

• Concentrated sulfuric acid, concentrated nitric acid, 80 degrees Celsius

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• Concentrated sulfuric acid, concentrated nitric acid, 30 degrees Celsius

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• Concentrated sulfuric acid, concentrated nitric acid, 60 degrees Celsius

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Arrange the steps in the correct sequence.

• KMnO₄, dilute H₂SO₄, heat

• CH₃Cl, anhydrous AlCl₃, room temp

• Br₂, anhydrous FeBr₃, room temp

Which of the following explains why benzene does not undergo addition reactions?

• Benzene is fully saturated.

• Benzene is electron-rich.

• Benzene contains a delocalised π electron cloud.

• Addition will cause benzene to lose the resonance stability.