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I have heard about activating ortho-para directors. For example: methoxy group, hydroxy group, alkyl group, et cetera.

I have heard about deactivating ortho-para directors. For example: halogen substituents

I have heard about deactivating meta directors. For example: nitro, trifluromethyl group, carboxylic acid group, et cetera.

So, naturally, I have embarked on a quest to find Activating Meta directors.

I have found one potential candidate, which is dimethylphenylborane:

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Boron possesses a vacant $\mathrm{p}_z$ orbital, which can interact with the $\pi$-cloud of the benzene ring.

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Considering the fact that boron is treated as a metalloid, it will definitely be less electronegative than carbon, so the dimethylborane group should offer a good +I effect, which could possibly outweigh the -M effects.

Can anyone shed some light on this issue? Are there any other examples of activating meta directors?

Pritt says Reinstate Monica
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    Related: https://chemistry.stackexchange.com/q/15973/4325 – jerepierre Jun 30 '17 at 07:11
  • You're talking about for EAS? – Zhe Aug 14 '17 at 14:48
  • @Zhe That's a positive. – Pritt says Reinstate Monica Aug 14 '17 at 15:49
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    OK. Got it. So what makes you think this is a +I effect? For example. how is having a borane on the ring any different from having a carbonyl attached to the ring? – Zhe Aug 14 '17 at 18:06
  • @Zhe First of all, I never confidently said that borane will give a +I effect, I only assume it to be so, since boron is quite electropositive compared to carbon, so it might tend to push the $\sigma$-electrons towards carbon. – Pritt says Reinstate Monica Aug 15 '17 at 01:52
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    Screwed up the first response I was trying to write... I think this is an interesting idea. You might even consider other substituents instead of methyl on the borane. – Zhe Aug 15 '17 at 02:09
  • @Zhe I first considered having hydrogens instead of methyl, but I decided not to do that since $\ce{B-H}$ bonds impart reducing properties to the molecule. – Pritt says Reinstate Monica Aug 16 '17 at 14:55
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    This is very theoretical, but what if you added a subtituent such as orthonitrate so that the formula is Na2O3NPh, basically a nitrogen attached to a phenyl with 3 oxygens single bonded to it. The meta directing would be done similar to the nitro group, due to recent evidence pointing towards the pentavalent nitrogen structure being a part of resonance, and then the carbon gains electron density because of the pentavalent structure being in resonance with the traditional structure (following octet rule). – AS_1000 Aug 17 '17 at 13:50
  • @AS_1000 I just looked up what orthonitrates were, and they don't seem to activating groups to me. Also, can you elaborate because of the pentavalent structure being in resonance with the traditional structure? – Pritt says Reinstate Monica Aug 17 '17 at 13:54
  • The activation is because it's like a phsophonium ylide (ammonium ylide) and the traditional structure is that of which follows the octet rules, I'll probably end up posting an answer to clarify, structures are required to explain. – AS_1000 Aug 17 '17 at 20:11

1 Answers1

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Note: This requires an extremely high energy scenario to occur.

This is another example that looks promising, it is essentially an ylide that has enough EWing power to meta direct while giving some density to the ring in another resonance structure. [Resonance]

The phosphonium ylide derivative (phenylphosphonic acid) may provide the same effect if the hypervalent nature of nitrogen is challenged, or if this substance is unobtainable under any circumstances.

AS_1000
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