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Is there a group that would attached to a benzene ring, donate electrons by inductive effect and withdraw them by conjugation?

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    $\begingroup$ Well, I guess a $\ce{-BH2}$ group attached to benzene ring would have this effect. It has an empty $\ce{p}$ orbital that would withdraw electrons via conjugation, but $\ce{B}$ is less electronegative than $\ce{C}$ and so it would have a positive inductive effect. $\endgroup$ – Philipp Sep 2 '14 at 19:58
  • $\begingroup$ Thank you for the answer. Now, an additional question: Where would substitution happen on the aromatic ring? $\endgroup$ – RBW Sep 2 '14 at 20:52
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    $\begingroup$ Usually conjugation beats inductive effects. So substitution should happen in the meta position. $\endgroup$ – Philipp Sep 2 '14 at 20:57
  • $\begingroup$ How probable is ipso substitution? $\endgroup$ – RBW Sep 3 '14 at 14:59
  • $\begingroup$ @Marko It's okay to ask a new question for follow-ups. If you want to reference that it's a continuation of this question, you can link to this one. $\endgroup$ – jonsca Sep 5 '14 at 20:14
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I guess a $\ce{-BH2}$ group attached to a benzene ring would have this effect. It has an empty $\ce{p}$ orbital that would withdraw electrons via conjugation, but $\ce{B}$ is less electronegative than $\ce{C}$ and so it would have a positive inductive effect.

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