The substituent effect on the UV energy of 4,4′‐disubstituted benzylideneanilines

Abstract

In this paper, 72 samples of disubstituted benzylideneanilines were all synthesized, and their UV data were measured in anhydrous ethanol. In the study on the UV energy of the titled compounds with single substituent changed, for the effect of the aniline substituent Y on the UV wavenumbers, its UV data can be correlated with a dual‐parameter equation; for the effect of benzylidene substituent X on the UV data, its UV energy can be correlated with a single‐parameter equation (Y is an electron‐withdrawing group and H) or a dual‐parameter equation (Y is an electron‐donating group). In the study on the UV energy of model compounds with double substituents changed, a correlation equation between the UV absorption wavenumbers and substituent constants σCCex and σp, was obtained. For 72 samples of 4,4′‐disubstituted benzylideneanilines, the correlation coefficient was 0.9876, and the standard deviation s was only 358.46 cm–1. The equation can be used to predict well the UV energy of BA derivatives. It was found that Δσ2 is a better parameter than σXY to scale the substituent cross‐interaction effect on the UV wavenumbers of benzylideneanilines molecules. The results implied that the law of substituent effect on the UV energy of titled compounds is different from that of substituted stilbenes, and it is helpful to understand the effect of substituent effects on the chemical and physical properties of conjugated compounds with an imine bridging group (C = N) or a nonplanar parent. Copyright © 2011 John Wiley & Sons, Ltd.

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 obtained results are as the following: the biggest ν max is 32154 cm ‐1 (λ max 311.00 nm) of p ‐FPNCN‐ m , and the least ν max is 25297 cm ‐1 (λ max 395.31 nm) of p ‐NO 2 PNNMe 2 ‐ p , in which the gap (Δλ max ) of λ max is only 84.31 nm, and is much less than that of XPEAYs. Here we also calculated the ν max of 72 samples of XBAY reported by Chen with equations (2) and (3) respectively, and obtained the gap (Δλ max ) 123.46 nm and 101.55 nm respectively. It also shows that the side‐group Me at carbon end increases the distribution of λ max .…”

“…These studies of substituent effects on the ν max of aryl‐Schiff bases show that not only the excited‐state substituent parameter , but also Hammett constant σ were employed in the quantitative correlations of the ν max . Wang even made an attempt of molecular design and synthesis of 3,4’/4,3’‐disubstituted benzylidene anilines with specified λ max , on the basis of Chen's report, in which the predicted λ max values are in agreement with the experimental ones for these designed compounds.…”

“…The spectrum of each target compound was tested for three times (the absorption spectra of XPNYs can be seen in the supporting information, the λ max values of XPEAYs come from the Cao's master thesis), then the mean value of λ max for each sample was employed in this work, The λ max values of all target compounds were collected and their λ max as well as ν max values (ν max =1/λ max ) were listed in Tables and . The ν max values of XBAYs were employed from Chen's report …”

“…Chen investigated the effects of substituents on the ν max of XBAYs and obtained the correlation equation (1). …”

“…Comparing with the C=C non‐polar bond in XSBY, there is a polar C=N bridging group in the disubstituted benzylideneanilines XArCH=NArY (abbreviated XBAY). By investigating 72 samples of XBAY, Chen et al proposed a penta‐parameter equation to quantify the ν max well. On the basis of the study on XBAY, we come up with another two series of compounds: one is the disubstituted N‐(phenyl‐ethylene)‐anilines XArC(Me)=NArY (abbreviated XPEAY) in which the H atom in CH=N is replaced by a methyl CH 3 (abbreviated Me); another is the disubstituted N‐phenyl‐α‐phenylnitrone XArCH=N(O)ArY (abbreviated XPNY) in which an O atom is attached to the N in CH=N.…”