A series of 15 4-substituted N-(4-nitrobenzylidene)anilines was synthesized and studied by 1H NMR spectroscopy. Their ab initio calculated geometries and the shielding as expressed by aromatic ring currents were used in correlation analysis. The geometries were fully optimized using density functional theory B3LYP/6-311G** approaches. For the determination of the ring current contribution to the shielding of azomethine hydrogens Hα was used direct ab initio calculation of the chemical shielding in a model system. Experimental chemical shift values free of these contributions were successfully correlated with increments ap of chemical shift for monosubstituted benzenes. In the same manner, the contribution of the anisotropy of C=N double bond to Hm hydrogen were calculated and values of the Hm chemical shift free of this contribution were successfully correlated with increments of chemical shift am.
一系列15个4-取代N-(4-硝基苯甲基亚胺)苯胺经过合成并通过1H核磁共振光谱进行研究。它们的从头算几何结构以及由芳香环电流表示的屏蔽效应被用于相关性分析。几何结构完全优化使用密度泛函理论B3LYP/6-311G**方法。为了确定环电流对偶氮甲基氢Hα屏蔽的贡献,使用了在模型体系中直接从头算化学屏蔽的计算。实验化学位移值中不包含这些贡献的部分成功地与对单取代苯乙烯的化学位移增量ap相关联。以相同的方式,计算了C=N双键对Hm氢的各向异性贡献,并且不包含这种贡献的Hm化学位移值成功地与化学位移增量am相关联。