Is the sulphonic acid group a benzene ring activating [ortho-para directing] or deactivating group [meta directing] ?

My thought: As highly electronegative O atoms are attached, the sulphonic acid group will take electron from benzene ring by negative inductive effect...So it would be meta directing.


It is a meta-directing group and a deactivating group because the $\rm -I$ effect of the group is quite strong and significantly outweighs that stabilization caused by conjugation (that you can describe with resonant structures).

Your question has some confusion in the concepts. A ortho-para-directing group is not necessary an activating group. Halogen is a typical counter example.

Your reasoning that highly electronegative O is attached and hence the group is meta-directing is incomplete because you fail to consider the conjugation. $-\rm OH$ is an example. It has $\rm -I$ effect, but is an ortho-para-directing and activating group.


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