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A short answer is that we mostly use resonance structures to represent delocalization when the bond orders or formal charges predicted by VBT are not approximately integers, simply because non-integer bond orders and charges are more cumbersome to draw. A typical example is a carboxylate, which we could draw with 1.5 bonds between both C-O pairs and -0.5 ...


3

I am not sure the 3D conformation stills as reported on PubChem are all that accurate. Although crystal structures are sometimes referenced for specific molecules, some of the displays are in fact models, some of which do not make sense to me. Here are some observations regarding the three molecules you noted. 2-Nitrobenzoic acid The PubChem model shows both ...


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You might be confused but not missing anything big or fundamental. A pi-conjugated system is one in which delocalisation of pi-electrons can take place. It is all. When effective, pi-conjugation is a subset, or a type, of delocalisation than can be described by resonance. However: to be strict, conjugation refers to bonds, and specifically to an alternating ...


2

Although the phenolate ion has more resonance structures (4) compared to acetate ion (2), acetate is more stable because it has two equivalent resonance structures of same energy. I would argue the phenolate ion has five mesomeric structures, two with the charge assigned to oxygen (analogous to the two resonance structures of phenol), and three with the ...


1

I'll provide a partial answer: resonance and delocalization are invoked to explain the fact that certain molecules do not have specific bonding patterns expected based on Lewis bond theory. In particular, that theory would predict that some molecules exist as mixtures of symmetry-related isoenergetic structures with some symmetry-related bonds differing in ...


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