Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (2): 204-210.doi: 10.3866/PKU.WHXB201412191


Effect of Substituents on the NMR and UV Spectra of N-(4-substituted benzylidene) Anilines and N-(4-substituted benzylidene) Cyclohexylamines

CAO Chao-Tun, WEI Bai-Ying, CAO Chen-Zhong   

  1. Hunan Provincial University Key Laboratory of QSAR/QSPR, Key Laboratory of Theoretical Organic Chemistry and Function Molecule of Ministry of Education, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, Hunan Province, P. R. China
  • Received:2014-09-24 Revised:2014-12-19 Published:2015-01-26
  • Contact: CAO Chen-Zhong
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21272063, 21072053) and Natural Science Foundation of Hunan Province, China (14JJ3112).


Two series of compounds: N-(4-substituted benzylidene) anilines (1) and N-(4-substituted benzylidene) cyclohexylamines (2) were synthesized. Their 13C NMR and 1H NMR chemical shifts and their UV absorption spectra were obtained. Compounds (1) and (2) were compared quantitatively to determine the effect of the substituents on the 13C NMR chemical shifts δC(C=N) and the 1H NMR chemical shifts δH of the CH=N bond, and the UV absorption maximum wavelength energies vmax. Our results show that the substituents affect compounds (1) and (2) differently despite them having a similar molecular skeleton. These effects are: (i) a substituent specific cross-interaction effect (Δσ2) that significantly affects the δC(C=N), δH, and vmax of compounds (1) while its effect on the corresponding properties of compounds (2) is limited, (ii) for compounds (1) and compounds (2) the field/induced effect σF and the conjugation effect σR of the substituents negatively affect δC(C=N). However, they positively influence δH and thus both σF and σR showopposite behavior toward δC(C=N) compared with δH. In contrast the field/induced effect greatly affects the δC(C=N) of both (1) and (2) but does not affect their δH, (iii) the regular change in δC(C=N), δH, and the vmax of (1) as well as (2) can be expressed by a general equation in which the effect of the phenyl group attached to the N atom of the CH=N bond can be expressed by a dummy parameter I. The phenyl group has a constant contribution toward these three properties.

Key words: Benzylidene-aniline, Substituent effect, Nuclear magnetic resonance, Ultraviolet absorption, Substituent specific cross-interaction