# Ipso substitution and its rules

I was taught that the following reaction happens:

It is called the "ipso-substitution". My professor had told me that it occurs in the case of $\ce{-SO3H}$ and $\ce{-COOH}$. But he had ended the topic there. My textbook doesn't detail any more either.

My searches landed me up at the fact that ipso-substitution is also employed in the preparation of picric acid from nitrobenzene. But I couldn't find answers all my other questions, which are:

1. Does the ipso-substitution occur only for these two groups, or are there more? I guess there is a "threshold" value for some parameter, above (or below) which ipso substitution cannot occur, but I am unable to come up with what that parameter is. I guess it's the high stability of the leaving group $\ce{SO3-}$, but I am not sure.
2. Is ipso-substitution affected by the choice of the electrophile and the solvent? What if, instead of bromine water, I chose bromine in acetic acid? Or something even simpler as $\ce{FeCl3/Cl2}$. Would ipso substitution occur then?
3. I know that no organic reaction produces 100% of only one compound, as its other isomers are always also formed. Ipso substitution should be no exception. But how do we decide whether the ipso product is a major product or a minor product? I know how to decide major/minor products between ortho/meta/para substitution (electron density/steric hindrance/H-bonding), but I haven't been taught any logic to decide the same for ipso substitution.
• I can't say that there is a set of rules for ipso substitution. For the loss of a more complex group by an ipso protonation, see chemistry.stackexchange.com/questions/50866/… – user55119 Apr 13 '18 at 20:45
• All "ipso" substitution means is that it occurs where the leaving group was. That's all. Essentially all of the $\mathrm{S}_{N}\mathrm{Ar}$ reactions you learn are ipso substitutions. – Zhe May 22 '18 at 20:51
• Trick to remember. All o/p positions wrt strongest activating group becomes br on addition on bromine water(irrespective of the group's there) – user600016 Jan 4 '19 at 15:16