Electrophilic Attack on Derivatives of Benzene | Organic Chemistry 2

The electrophilic attack on derivatives of benzene are studied in this chapter: the electrophilic substitution of substituted benzenes, the activators and deactivators substituents, the meta- ortho- para- directing substituents, the synthetic strategies.

Electrophilic Substitution of Substituted Benzenes

Substituents on benzene can be grouped into:

- activators (electron donors) ⇒ second electrophilic attack to the ortho and para positions
- deactivators (electron acceptors) ⇒ second electrophilic attack to the meta positions

Induction and Resonance = 2 main effects for the activation or the deactivation

 

Activated Benzene:

 

D ⇒ Donor:
- NH2, OH (strongly activating)
- NHCOR, OR (moderately activating)
- alkyl, aryl (weakly activating)
- halogen


 

Deactivated Benzene:

 

A ⇒ Acceptor:
- N+R3, NO2, CF3, CN, SO3H (strongly deactivating)
- COH, COR, COOH, COOR, CONH2 (moderately deactivating)


 

Selectivity:
- the position of attack is controlled by the strongest activator (and then by steric effects).
- para product is preferred over ortho product because of steric effects.

Synthetic Strategies

Changing the sense of the directing power of substituents:
 


 

Blocking / Deblocking a position:
 


 

Moderation of Strong Activators ⇒ change the selectivity of the Electrophilic Attack: