Aromaticity and aromatic compounds:
- Planar with delocalized π electrons
- Multiple resonance structuresVery stable
- All C-C bond angles are 120°
- Each carbon is hybridized
- Each carbon has a p orbital perpendicular to the plane of the ring
Rule1: it must have an uninterrupted cyclic cloud of π electrons above and below the plane of
- π cloud: molecule must be a planar.
- Cyclic: the molecule must be cyclic and have double bonds
- Uninterrupted: All carbon atoms are carbons.
Rule 2: the π cloud must have an odd number of pairs of π electrons.
- Ends with –benzene
-alkyl group: Propylbenzene
-nitrate group: Nitrobenzene (NO )
- Alternate groups:
- Toluene(-CH )
- Aniline(-NH )2
- Benzoic acid(-COOH) Disubstituted benzene:
- Ortho-(o): 1, 2 disubstituted
- Meta-(m): 1, 3 disubstituted
- Para-(p): 1,4 disubstituted
More than 2 substituent’s
- Substituent’s listed alphabetically
- Lowest possible numbers used
Reactivity of benzene:
Reactants: halogens+ catalyst (FeBr )
Example: - Nitration/ Sulfonation:
Reactants: HNO / SO +Catalyst (H SO )
3 3 2 4
- Fredial-Crafts Alkylation/Acylation:
Reactant: alkyl halides/ acyl halides + catalyst (AlCl ) 3
Example: - Oxidation of the alkyl groups: * aromatic ring don’t react with the catalyst.
Reactant: alkylbenzene + Catalyst (KMnO +H 4) 2
Effect of the Substituent’s:
Formation of the carbocation is the rate determining step and anything that helps or hinders
this affects reactivity.
- Donating and withdrawing electron inductively through the Ϭ bonds
Alkyl substituents: the electrons in the Ϭ bond move towards benzene.
making it more stable
Substituents is more electronegative than carbon: the electrons in the Ϭ bond move
away from benzene
making it less stable
Example: -NO ;2Cl ;-Br
- Donating and withdrawing electrons by resonance through the π bonds
Substituent is directly attached to the benzene has a lone pair, the lone pair can be
delocalized into the ring
A –ve charge makes the ring more reactive (activators)