Reactions and Reagents:
The following table contains a summary of the key reactions of aromatic systems covered by this topic. More detailed information on each reaction can be accessed by following the link above. Note that the reagent combination and reaction conditions for reactions of benzenes are usually more severe than reactions of alkenes.... this tends to make them more readily recognisable.
The notes on the physical propoerties, are followed by the reacions. The biggest group of reactions is the electrophilic subsitutions. there are two addition reactions and a subsitution in "4"
| 1 | Structure of Benzene | ||||
| 2 | A Modern view of the Structure of Benzene | ||||
| 3 | Spectral evidence | ||||
| 4 | Addition Reactions | H2 Cl2 And Combustion | H2 Cl2 O2 | Combustion is not an addition reaction! | |
| Reaction | Reagents | Electrophile | Product | Comments | |
| 4 | Halogenation | Cl2 / Fe or FeCl3 | Cl+ |
 |
E+ formed by Lewis acid removing Cl- |
| 5 |
|
|
|
 |
E+ formed by loss of water from nitric acid |
| 6 |
|
H2SO4 or SO3 / H2SO4 |
|
 |
Reversible |
| 7 |
|
|
|
 |
E+ formed by Lewis acid removing Cl- |
The following pointers may aid your understanding of the subsitution reactions:
- Recognise the electrophile present in the reagent combination
- The electrophile adds first to the arene
- Substitution is preferred over addition in order to preserve the stable aromatic character
© LEV