4
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This is (alkanesulfinyl)benzene:

enter image description here

I didn't draw it, but we know that the sulphur atom also has a lone pair. So, the sulphur atom can increase electron density in the ring by donating a lone pair. However, oxygen can also withdraw electron density from the ring by pulling back an electron pair. They both are contradictory, so which effect dominates? What is the final directing effect of the alkanesulfinyl group?

That said, I am not entirely sure if what I said above is 100% correct. The reason being that since the sulphur atom is sp3 hybridized, it is tetrahedral in shape, and not planar. So, either the sulphur's lone pair or the oxygen's pi bond will be out of the plane (but not both at once), and won't take part in any delocalisation. But we can't theoretically predict which one it would be, can we?

If there could be experimental evidence to support the claim whether it is meta-directing or o/p-directing, that would be even more beneficial. I have checked both Wikipedia and masterorganicchemistry, and neither even mentions this functional group, let alone its directional nature.

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  • $\begingroup$ chemistry.stackexchange.com/questions/88111/… confirms it's tetrahedral $\endgroup$ – Mithoron Mar 17 '18 at 20:34
  • $\begingroup$ Situation may be similar as in chemistry.stackexchange.com/questions/8509/… or in protonated amines $\endgroup$ – Mithoron Mar 17 '18 at 20:35
  • $\begingroup$ I think it will be o-p directing. I don't have any theoretical reasoning for it but just a comparison with Ph-NO. In this molecule too there is a lone pair on N and a pi bond. As a fact I know that NO is o-p directing. So, I'm assuming that the compound you gave might also be o-p directing. $\endgroup$ – FreakyLearner Mar 22 '18 at 13:43
  • $\begingroup$ @user26732 Thanks for dropping by! Though I think the distinction here between Ph-NO and Ph-SOR is that - correct me if I'm wrong though - the former is linear but the latter is tetrahedral. $\endgroup$ – Gaurang Tandon Mar 22 '18 at 13:50

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