Influence of the side-group at C=N bridging bond of bis-aryl Schiff bases on the wavelength of absorption maximum of ultraviolet absorption spectra

The compounds N-(benzylidene)-anilines XArCH=NArY (XBAY), N-(phenyl-ethylene)-anilines XArC(CH3)=NArY (XPEAY) and N-phenyl--phenylnitrones XArCH=N(O)ArY (XPNY) have bridging group CH=N, C(CH3)=N and CH=N(O) respectively, in which the C(CH3)=N has a side-group methyl CH3 at carbon end and the CH=N(O) has a side-group O atom at nitrogen end. In this work, a series of XPEAY and XPNY were synthesized, and their longest wavelength maximum (max) (nm) of ultraviolet absorption spectra were measured. Then the change regularity of the (max) (cm(-1), (max)=1/(max)) of XPEAY and XPNY were investigated, and they were compared with that of XBAY (reported by ref.26). The results indicate: (1) There are no good linear relationships between the (max) of XBAYs and XPEAYs or XPNYs. (2) In case of a same set of X-Y group couples, the distribution of (max) of XPEAYs is larger than that of XPNYs. (3) The side-group CH3 makes the effect of sigma(X) larger than that of sigma(Y) on the (max) of XPEAYs, whereas the O atom makes the effect of sigma(Y) larger than that of sigma(X) on the (max) of XPNYs. (4) The cross-interaction between X and Y has important effect on the all (max). However, the cross-interaction between CH3 and X/Y has not important effect on the (max) of XPEAY, and the cross-interaction between O and X/Y has not important effect on the (max) of XPNY. Copyright (c) 2016 John Wiley & Sons, Ltd.