Collect. Czech. Chem. Commun. 2004, 69, 1566-1576

Modeling Substituent-Dependence of the Twist and Shielding in a Series of 4-Substituted N-(4-Nitrobenzylidene)anilines

Vladimír Proks* and Miroslav Holík

Department of Theoretical and Physical Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 610 37 Brno, Czech Republic


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.

Keywords: Ab initio calculations; Correlation analysis; Azomethines; 1H NMR chemical shifts; Imines; Substituent effects; Conformation analysis; NMR spectroscopy.

References: 43 live references.