Angular Group Induced Bond Alternation (AGIBA). Part 4: Does the Effect Operate in the Systems with Alternated Bonds?

Angular groups attached to non-cyclic π-electron systems like amidine or 1,3-butadiene do not exhibit the AGIBA effect, whereas when attached to aromatic systems they act in an ambiguous way—the effect is much more local than in the cases observed in monocyclic systems (benzene, s-triazine). The above picture is based upon ab initio calculations at B3LYP/6-311+G∗∗ level of theory for 2,3,6,7- and 1,4,5,8-tetramethoxynaphthalene, 9,10-dimethoxyphenanthrene, 4,9- and 4,10-dinitrosopyrene derivatives of C2 or i symmetry, and X-substituted 1,3-butadiene (X=NO, CHO, NNH, CHCH2 and OCH3) at B3LYP/6-31G∗ for C- substituted derivatives of formamidine substituted derivatives of formamidine (X=NO, CHO, NNH, CHCH2, OCH3 and CH2CH3).