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1

Why was Kekule's model disproved?

Hydrogenation energy is less exothermic than expected - benzene is more stable than Kekule's model
All bond lengths are equal
Lack of reactivity - bromine does not decolourise bromine water or undergo electrophilic addition

2

What type of reaction does benzene undergo?

Electrophilic substitution

3

Nitration of benzene

Conc HNO3 and conc H2SO4 (catalyst)
NO2+

4

Halogenation of benzene

Halogen (Cl/Br) and halogen carrier (AlCl3, AlBr3, FeCl3, FeBr3, catalyst)
Cl+/Br+

5

Friedel-crafts alkylation of benzene

Chloroalkane + AlCl3 (catalyst, anhydrous)

6

Friedel-crafts acylation of benzene

Acyl chloride + AlCl3 (catalyst, anhydrous)

7

Comparing reactivity: alkenes vs arenes
Bromination

Benzene does not react with bromine without a halogen carrier due to the delocalised pi electrons which have a lower electron density than C=C and therefore cannot polarise Br2

8

What is phenol?

OH directly attached to C6H6
Non polar benzene ring makes phenol less soluble and is classified as a weak acid
When OH is attached to a side chain (benzene) it is classified as an alcohol

9

Neutralisation
Phenol + NaOH

Salt + H2O

10

Bromination
Phenol + 3Br2

2,4,6-tribromophenol + 3H2

11

Nitration
Phenol + HNO3 (dilute)

2-nitrophenol/4-nitrophenol

12

Why does phenol react more readily than benzene?

Lone pair of electrons from the oxygen p orbital (OH) is donated in the pi system of phenol - increased electron density attracts electrophiles therefore more susceptible to attack. The electron density is sufficient enough to polarise bromine molecules

13

Directing groups OH, NH2, NO2

OH, NH2 : 2,4-directing
Electron donating
Activates aromatic ring
NO2 : 3-directing
Electron withdrawing
Deactivates aromatic ring