Arenes

State the general formula of benzene

1. C6H6.

Compare the reactivity between benzene and alkene

1. For both benzene and alkene, the pi electrons are loosely held and hence are available to react with electrophiles. Hence, both benzene and alkene undergo electrophilic reactions.

2. Benzene requires stronger electrophile to react. Resonance stabilisation causes the pi electron cloud to be less reactive than C=C and requires a stronger electrophile to react.

3. Benzene undergoes substitution rather than addition due to the resonance stabilisation from the delocalisation of the pi electron cloud. Addition will destroy the stable aromatic structure of the ring.

State the reagents and conditions necessary for electrophilic substitution of halogens of benzene

1. Br2(l), AlBr3 catalyst, r.t.p.

2. Cl2(g), AlCl3 catalyst, r.t.p.

State the reagents and conditions necessary for nitration of benzene

1. Concentrated HNO3, concentrated H2SO4, maintained at 50 degrees celcius.

State the reagents and conditions necessary for friedal crafts alkylation of benzene

1. CH3CH2Cl, AlCl3 as catalyst, r.t.p.

State the reagents and conditions necessary for free radical substitution of benzene side chain

1. Limited Cl2(g), UV light, r.t.p.

State the reagents and conditions necessary for oxidation of benzene side chain

1. Acidified KMnO4(aq), heat under reflux.

2. Hot alkaline KMnO4(aq), dilute acid.

Describe the effect of electron donating R groups on the reactivity of benzene

1. Electron donating R groups activates the benzene ring towards electrophilic substitution by increasing electron density in the ring and hence the benzene ring becomes more reactive.

2. 2- and/ or 4- directing.

Describe the effect of electron withdrawing groups on the reactivity of benzene

1. Electron withdrawing groups deactivates the benzene ring towards electrophilic substitution by decreasing the electron density within the ring and hence the benzene ring is less reactive.

2. 3- directing.