Anywhere I look, I get 3 resonating structures for CO molecule, like in this answer.
However, according to the rules stated for drawing resonating structures in this site, I wonder why there can't be this resonating structure as well?
Although it will be very unstable (due to lesser number of covalent bonds, positive charge on more electronegative atom), yet a minute contribution of this structure must in present in the resonance hybrid of the CO molecule. Then why is this structure not shown anywhere?
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asked Jun 10, 2016 at 7:15
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4$\begingroup$ For exactly the reason you have said. It contributes a very minor component to the overall structure. There are an awful lot of possible resonance structures but very few of them are significant contributors. $\endgroup$– bonJun 10, 2016 at 9:17
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1 Answer
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You have said it yourself. There are many possible resonance structures but most of them have a negligible contribution to the overall structure. Your proposed structure is one of them.
The major resonance contributors of carbon monoxide are: $$\ce{\!\overset{\ominus}{C}#\overset{\oplus}{O}\! ~<->~ \!C=O\! ~<->~\!\overset{\oplus}{C}-\overset{\ominus}{O}\!}$$
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$\begingroup$ The carbon atoms in the last two contributing canonical forms are not in octet condition. Isn't that a problem? $\endgroup$– MrAPAug 22, 2017 at 18:49