[JohnTan]

Hi everyone,
I just have a query about the products of an electrophilic aromatic substitution. In my notes, there is an example where toluene undergoes nitration to give 2,4,6-trinitrotoluene. I realise that since the alkyl substituent is activating, nitronium ions will add to ortho and para positions. However, in all other examples in my notes, e.g. toluene + Br2/FeBr3 there are two products, one with the bromine in the ortho position and a seperate one with the bromine in the para position. Is trinitrotoluene an anomaly where substituents are added to all 3 positions? How can I anticipate if there will be two seperate products or just one?
Many thanks in advance

[Schrödinger]

Case 1 : Nitration :

Nitro group is meta directing... methyl group is ortho/para directing. So, when one nitro group has been added to the ring(say ortho to the methyl), the 2nd one can be added to 4/6, both of which are activated positions for nitration because of reinforcement from both the groups present. i.e., both methyl and the nitro group direct the next nitro group to the same positions.


Case 2 : Bromination :

Br and CH₃ are both ortho/para directors. So, lets say one Br has been added to the ring (say the product is orthobromotoluene). Now to which position is the next Br directed by the groups that are already present?
Answer : CH3 directs the next Br to 4 and 6. Br directs it to 3 and 5. As you can see, there is no position that predominates the other in preference of being substituted...All are possible to the same extent. Hence, the 2 major products can be regarded as ortho and para bromotoluene. Monobrominated products will be produced in more yield than the di/tri substituted ones.

I hope I've made myself clear... If not, please don't hesitate to ask

[JohnTan]

ahh terrific.
Thanks very much.