[daf44]

Hi,

Why does the bromination of toluene mainly gives para-bromotoluene, while the nitration of toluene mainly gives ortho-nitrotoluene?

[Nosterius]

This is a really good question.

Are you new to electrophilic aromatic substitution? Do you have some basis in frontier orbitals? And in hard-soft acids and bases?

[daf44]

I'm not new to E.A.S. and I have some basis about HOMO/LUMO and soft/hard bases ans acids.

[Nosterius]

You should take a look into Ian Fleming's "Frontier Orbitals and Organic Chemical Reactions".

In short, what I was able to find in there is that the harder the electrophile, the less ortho/para selective it is. That is, nitronium (NO2+) is much harder than bromine (Br2).

I am still trying to find the "why" of this, but I currently do not have the time to reread chapters 1-3 of this book right now.

I hope this helps...

[discodermolide]

This is a really good question.

Are you new to electrophilic aromatic substitution? Do you have some basis in frontier orbitals? And in hard-soft acids and bases?

Perhaps you should take a look at this review in Angewandte chemie
Farewell to the HSAB Treatment of Ambident Reactivity
Herbert Mayr,* Martin Breugst, and Armin R. Ofial
DOI: 10.1002/anie.201007100
Published this year in the ASAP's