Hi I think my approach to this is - Is there a resonance form in which the ring in question in unequivocally aromatic and the separated charge ends up somewhere sensible? The 'electron stealing' concept is a sort of handy shortcut for this.
For Greg's examples, I'd say: [image: image.png] I'm not sure I understand the 'If a "more electronegative atom" is valence saturated and has a double bond to a C, then it contributes two electrons to whatever ring system it's in' statement. The key thing is probably that the 'more electronegative atom' has to be outside the conjugated, potentially aromatic ring-system. Following this analysis means you don't need to consider the resonance form: A carbonyl or imine (open chain or in a partially saturated ring) group's carbon atom provides (effectively) 0 pi electrons 'Ordinary' aromatic carbons provide 1 pi-electron Pyridine-type nitrogens (2-connections) or pyridinium (3-connections) provide 1 pi-electron Pyrrole-type nitrogens (3-connections) provide 2 pi-electrons. So for example 3, that's [image: image.png] 10 pi-electrons in total, so the *system* is aromatic even though the electron counts look odd on a per-ring basis (not unlike azulene). I hope that makes sense! Chris On Tue, 23 Oct 2018 at 16:17, Greg Landrum <[email protected]> wrote: > > On Tue, Oct 23, 2018 at 5:14 PM Greg Landrum <[email protected]> > wrote: > >> >> That certainly handles the things we've discussed so far, as well as easy >> cases like pyridine and quinone. Now I need to try and find some stuff that >> breaks it. >> >> > What I should have added to this: I don't think it can possibly be this > simple, so I'm guessing those examples are out there. > > -greg > > _______________________________________________ > Rdkit-discuss mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/rdkit-discuss >
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