We find, for example, that nitration of nitrobenzene occurs smoothly at 95 ºC, giving meta-dinitrobenzene, whereas bromination of nitrobenzene ferric catalyst requires a temperature of 140 ºC.
These groups are called meta-directing groups, e.
We have already analyzed the activating or deactivating properties of substituents in terms of , and these same factors may be used to rationalize their influence on substitution orientation.
The mechanism above shows that when electron density is withdrawn from the ring, that leaves the carbons at the ortho, para positions with a parital positive charge which is unfavorable for the electrophile, so the electrophile attacks the carbon at the meta positions.
Its molecular fragment can be written as C 6H 5CH 2-R, PhCH 2-R, or Bn-R.
When the molar ratio of benzene to alkyl halide falls below 1:1, para-ditert-butylbenzene becomes the major product.