This is a cute example. The left ring is one in which every atom and every bond is aromatic, and yet the ring is not aromatic. Unlike azulene, in which neither ring, alone, is aromatic
On Tue, Oct 23, 2018 at 12:36 PM Greg Landrum <greg.land...@gmail.com> wrote: > > I'll try later (likely tomorrow) to explain what I meant a bit better. Or > maybe I'll just implement it (since it seems like it could be fairly easy). > > On Tue, Oct 23, 2018 at 6:13 PM Chris Earnshaw <cgearns...@gmail.com> > wrote: > >> >> 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). >> > > On this specific instance: This is exactly what the RDKit currently does. > However, in this scheme the left ring, which has 7 pi electrons, is not > aromatic even though both the right ring and the envelope are. > > -greg > > > _______________________________________________ > Rdkit-discuss mailing list > Rdkit-discuss@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/rdkit-discuss >
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