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确定了 N-苄叉基 -2 -氨基噻唑 ( 2 a)和 N-对硝基苄叉基 -2 -氨基噻唑 ( 2 b)的晶体结构 .结合已报道的N -对硝基苄叉基 -2 -氨基嘧啶 ( 1 a) ,N -对硝基苄叉基 -2 -氨基吡啶 ( 1 b)和 N -苄叉基 -3-氨基吡啶 ( 2 c)的晶体结构 ,利用 AM1 ,RHF,DFT方法和 6-31 1 G,6-31 1 G* * 基组 ,优化每个分子的 2 2个旋转构象 (θ=0°～ 90°) .由 DFT法所得到的最优构象的扭角 θ( 1 a,2 2°;1 b,0°;1 c,4 2°;2 a、 2 b:0°)与实验值 ( 1 a,2 6°;1 b,2 0°;1 c,4 6°;2 a,8.8°;2 b,3.8°)最接近 .尽管分子最优构象扭角的差异很大 ,但总电子能最稳定的构象都在 θ=±4 2°附近 .在任一分子、任何电子态中 ,离域的 π体系总是失稳定的 ,全平面构象不是 π体系最稳定的构象 .无论是离域的还是定域的π体系 ,它们均倾向于扭曲的几何构象 .π电子的离域是分子扭曲的驱动力之一 .与经典观点相反 ,非键原子间的核排斥作用是分子扭曲的阻力 ,而不是动力 .
The crystal structures of N - benzylidene - 2 - aminothiazole (2 a) and N - p - nitrobenzylidene - 2 - aminothiazole (2 b) were determined. (1 a), N - p - nitrobenzylidene - 2 - aminopyridine (1 b) and N - benzylidene - 3 - aminopyridine (2 c) using AM1, , The DFT method, and the 6-31 1 G, 6-31 1 G * * basis set to optimize 2 2 rotational conformations per molecule (θ = 0 ° to 90 °). The optimal conformation The torsional angles θ (1 a, 2 2 °; 1 b, 0 °; 1 c, 4 2 °; 2 a, 2 b: 0 °) were compared with the experimental values ; 1 c, 4 6 °; 2 a, 8.8 °; 2 b, 3.8 °). Although the difference in the optimal conformation angle of the molecule is quite large, the most stable generalized electron conformation is at θ = ± 4 2 ° In any molecular or any electronic state, delocalized π systems are always unstable and the full-plane conformation is not the most stable conformation of the π system. Both delocalized and localized π systems tend to Distorted geometric conformations. The delocalization of π electrons is one of the driving forces behind molecular distortions. Contrary to classical belief, nuclear repulsion between nonbonding atoms is molecularly distorted Resistance, rather than power.