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The lone pair of phosphorus and the double bonds in benzene looks to be in conjugation. Do the molecule show resonance? If so, how?

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    $\begingroup$ The final arbiter will probably be some computational study, but phosphorus 3p overlap with carbon 2p is not great to begin with. $\endgroup$ – orthocresol Apr 6 '17 at 17:15
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    $\begingroup$ Somewhat related, since the lone pair of the $\ce{P}$ atom is addressed: chemistry.stackexchange.com/questions/38599 $\endgroup$ – Klaus-Dieter Warzecha Apr 6 '17 at 17:36
  • $\begingroup$ @orthocresol,What do you think about the answer below? $\endgroup$ – Kai Hiwatari Apr 6 '17 at 18:01
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    $\begingroup$ There's probably no question that some degree of resonance exists; and indeed it's not possible for donation into all 3 rings to happen at once. However, the devil is in the details: how much of it is there? I personally don't know, but I don't think it's a lot, at least simply based on overlap arguments. $\endgroup$ – orthocresol Apr 6 '17 at 18:31

The triphenylphosphine molecule would show resonance because there is a lone pair on phosphorus and it is in conjugation with the double bonds in benzene. But the lone pair would be in resonance only with one ring at a time because the molecule is non-planar (tetrahedral) having sp3 configuration. Also, we should consider the steric effects on the molecule. The steric hindrance produced by other two benzene rings would cause less resonance effect and the lone pair would be inhibited from going into the other two rings. So, the resonance in this molecule would be simply like that in aniline.enter image description here


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