Benzene

Question 1

Bonding in benzene

Answer 1

• does not take part in addition reactions as it has no double bonds
• sigma bonds between carbons
• unhybridised p orbitals on each of the 6 carbons

Question 2

Why does benzene not undergo addition reactions?

Answer 2

Because it is relatively stable due to the delocalised electrons in the pi electron cloud. Addition reactions would lead to a disruption of the pi electron cloud and delocalisation and so would reduce the stability of the benzene ring.

Question 3

What kind of reactions does benzene undergo?

Answer 3

Electrophilic aromatic substitution as the electron rich pi cloud makes benzene susceptible to attacks by electrophiles

Question 4

Reactions

Answer 4

• alkylation
• halogenation
• nitration
• sulfonation

Question 5

Alkylation

Answer 5

Benzene will react with a haloalkane in the presence of aluminium chloride as a catalyst. The haloalkane and the aluminium chloride react together to form the alkyl electrophile. The CH3+ is the electrophile

Question 6

Halogenation

Answer 6

Benzene will react with bromine or chlorine in the presence of aluminium chloride, iron(III) bromide or iron(III) chloride as a catalyst. The Cl+ or Br+ acts as the electrophile.

Question 7

Nitration

Answer 7

Benzene will react with a concentrated nitric acid and concentrated sulphuric acid to make nitrobenzene. The concentrated acids react together to form the nitronium ion (NO2+) which is the electrophile.

Question 8

Sulfonation

Answer 8

Benzene will react with concentrated sulphuric acid to make benzesulfonic acid. The electrophile is generated by concentrated sulphuric acid (HOSO4+)