Effects of molecular conformation on the spectroscopic properties of 4,4 '-disubstituted benzylideneanilines

摘要

The relationship between the molecular conformation and spectroscopic properties of unsymmetrical 4,4'-disubstituted benzylideneanilines, was explored by the combination of experiment and reference data. Crystal structure information and spectroscopic behaviors of the seventeen samples p-X-C6H4CH= NC6H4-p-Y (X = NMe2, OMe, Me, Cl, CN, or NO2, Y=NMe2, OMe, Me, Cl, CN, or NO2) were provided for this study. Among these seventeen compounds, nine ones were synthesized firstly, and five crystal structures were determined and analyzed. It was observed that the twist angle of the aniline ring with respect to the rest of the molecule (tau) is systematically controlled by the substituent at the aromatic ring. The correlation results show that the UV maximum absorption in wavenumbers (upsilon(max)) is dependent on the substituent at the aromatic ring and the dihedral angle tau of the titled molecules, and a sine function of tau (sin(tau)) is suitable to modify the substituent effects on the upsilon(max). However, the dihedral angle tau has a limited effect on the values of C-13 NMR chemical shifts delta(C)(C=N). The results indicate that the dihedral angle tau has an significant effect on UV spectra of Schiff bases with different parent structure although there is something different about the parameter metrics. While it has a relatively limited effect on the values of delta(C)(C=N) in both unsymmetrical and unsymmetrical Schiff bases. This study provides an sufficient evidence of the molecular conformation on spectroscopic properties of Schiff bases. (C) 2015 Elsevier B.V. All rights reserved.