6.1.4 Directing Effects

Electron donating and electron withdrawing sides groups

• Side groups on a benzene ring can affect the position on the ring of substitution reactions
• Groups which are electron donating such as -CH₃, -OH and -NH₂ will force further substitutions to occur in the 2- and 4- positions on the benzene ring
• Groups that are electron withdrawing such as -NO₂ will forces substitution in the 3- position 
• We can use the directing effect of substitute the groups when planning an organic synthesis
• If a -OH group, a Cl atom or an -NH₂ group is directly bonded to a benzene ring, the delocalisation in the ring will extend to include the lone pairs from the N, O and Cl atoms
• This changes the properties and the reactions of the side group

• Due to the electron donating alkyl group in methylbenzene, nitration of methylbenzene will occur on the 2 and 4 position

Nitration of methylbenzene 

Chlorobenzene 

• Typical halogenoalkane and elimination reactions do not occur 
• Electron rich benzene ring will repel nucleophiles

Phenol 

• Delocalisation makes the C-O bond stronger and the O-H bond weaker
• It is more acidic than alcohols and also will not oxidise 

Phenylamine

• Phenylamine is less base aliphatic amines as lone pair is delocalised
• Therefore it the lone pair is less available for accepting a proton 

Phenylamine is less basic than an amine such as ethylamine due to the lone pair involvement of the delocalised electron ring