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I'm new to Organic chemistry, and I'm just starting to learn about resonance. I learnt that resonance and conjugation are related - if a system is conjugated, with alternating sigma and pi bonds/pi-sigma-lone pair/pi-sigma-free radical/pi-sigma-p orbital/lone pair-sigma-positive charge arrangements in the same plane, we can derive resonance structures by alternating the bonds/radical/charge between atoms. My question is - can resonance occur without conjugation, and if so, what are the rules governing it?

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A good example would be a polar covalent bond; such a bond exists as a resonance hybrid of totally covalent and totally ionic canonicals; switching on and off the (line in a Lewis stucture) respectively.

For example, the carbon tetrafluoride molecule* is covalent but has significant contributions from an ionic structure involving "a carbon(IV) cation electrostatistically bound to four fluoride anions" in tetrahedral symmetry- a "no lines, just ionic bonds" canonical.

*which is non-polar but still has polar covalent bonds in it

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  • $\begingroup$ So basically resonance can even occur on the types of bond (ionic or covalent) as well as pi-bond and lone pair structures? And are there any other arrangements in which something similar can happen? $\endgroup$
    – AlphaRogue
    Aug 14, 2021 at 6:47
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    $\begingroup$ Yes it can- both theoretically and empirically. $\endgroup$ Aug 14, 2021 at 6:49
  • $\begingroup$ Are there any other arrangements in which something similar can happen? $\endgroup$
    – AlphaRogue
    Aug 14, 2021 at 6:49
  • $\begingroup$ OP - Beware that it is difficult to pose a limit on the extent of the delocalisation and or the number of limiting forms, in principle. Then we use criteria. Also, and in reverse, the fact that a system is conjugated does not strictly implies delocalisation. At least you can conceive comformers right tilted so that delocalisation does not occur. $\endgroup$
    – Alchimista
    Aug 14, 2021 at 11:24
  • $\begingroup$ I think this is stretching the concept of resonance a bit thin, but definitely one point of view. It is rather important to understand the points that arise through this view, especially Valence bond methods, and those seemingly opposite to that view, e.g. molecular orbital theory.// Anyway, there is a typo, cation twice, you might want to fix. $\endgroup$ Aug 29, 2021 at 15:01

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