In this work, 13 compounds of 4,4′‐disubstituted stilbenes and 5 compounds of 3‐methyl‐4′‐substituted stilbenes were prepared and their UV spectra were measured. A new substituent effect constant, namely excited‐state substituent constant, was proposed, which was calculated directly from the UV absorption energy data of substituted benzenes. The investigation result shows that the proposed constant is different from the existing polar substituent constants and radical substituent constants in nature. The availability of the new constant was confirmed by the good correlations with the UV absorption energy of four kinds of compounds, 1,4‐disubstituted benzenes, 4,4′‐disubstituted stilbenes, substituted ethenes, and m‐Y‐substituted aromatic compounds. It is expected that the excited‐state substituent constant can be applied in QSPR study on organic compounds at the excited state. Copyright © 2008 John Wiley & Sons, Ltd.
The substituent effect on 13 C NMR of the C --N in benzylidene anilines XPhCH --NPhY was investigated, in which the substituents X and Y are in p-position or in m-position of the two aromatic rings. The substituent effects including the inductive effects of X and Y, the conjugative effects of X and Y, and the substituent specific cross-interaction effect were put into one model to quantify the 13 C NMR chemical shift d C (C --N) of the C --N in XPhCH --NPhY. A penta-parameter correlation equation with correlation coefficient 0.9975 and standard error 0.17 ppm was obtained for 80 samples of compounds. The result shows that the substituents X and Y have an opposite effect on the d C (C --N). The electron-withdrawing effects of X decrease the d C (C --N); while the electron-donating effects of X increase the d C (C --N). In contrast, the electron-withdrawing effects of Y increase the d C (C --N); while the electron-donating effects of Y decrease the d C (C --N). A new substituent specific cross-interaction effect parameter Ds 2 was proposed, which indicates that the most substituent specific cross-interaction effect exists in the pair of max electron-withdrawing group (EWG) and max electron-donating group (EDG) or the pair of max EDG and max EWG. Further to verify the obtained correlation equation, 15 samples of model compounds were prepared and their d C (C --N) was measured in this work. The predicted d C (C --N) values with the obtained equation are in good agreement with the measured ones for these prepared compounds, which confirmed the reliability of the obtained equation.By fixing the substituent X (or Y) at one end, Neuvonen [1,7] recently investigated the substituent cross-interaction effects on the electronic character of the C --N bridging group in substituted benzylidene anilines XPhCH --NPhY with the 13 C NMR spectra of C --N carbon. He obtained the valuable results:(1) for the X substituents: electron-withdrawing group (EWG) cause shielding, while electron-donating group (EDG) behave oppositely; (2) in contrast, for the Y substituents: EWG cause deshielding, while EDG cause shielding of the C --N carbon. Also, (wileyonlinelibrary.com)
In this paper, 61 samples of 3,4'-disubstituted stilbenes and 18 samples of 3,3'-disubstituted stilbenes were synthesized, and their UV data were measured in anhydrous ethanol. Based on the UV absorption energy (wavenumber) of 3,4'-disubstituted stilbenes, the excited-state substituent constants s ex CC m ð Þ of metasubstituent were determined by means of curve-fitting. The availability of s ex CC m ð Þ was confirmed by the good correlation with the UV absorption energy of 3,4'-disubstituted stilbenes and 4,4'-disubstituted stilbenes. Further, using the obtained constants s ex CC m ð Þ and the correlation equation, we calculated the UV wavenumbers of 3,3'-disubstituted stilbenes, and the calculated wavenumbers are in good agreement with the experimental values. These results verified that the excited-state substituent constants s ex CC m ð Þ of meta-substituent are reliable parameter to scale the effect of meta-substituent on the UV absorption energy.
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.
Three parameters, ${\rm \sigma }_{\rm CC}^{\rm ex} $, ${\rm \sigma }_{\rm CC}^{\rm ex} ({\rm XY)}$ and $\upsilon_{{\rm max,}\,{\rm parent}} $, are developed to express the substituent effect and the effect of the parent molecular structure of p‐disubstituted compounds XPh(CHCHPh)nY (n = 0, 1, 2). The investigated result shows a good correlation between the UV absorption wavenumbers (υmax) and the three parameters for a diverse set of title compounds, and the correlation equation can be used to predict the UV absorption energy of compounds with the mentioned structure. This approach provides a new insight for the quantitative structure‐property relationship (QSPR) correlation of the UV absorption energy of p‐disubstituted homologues. Copyright © 2010 John Wiley & Sons, Ltd.
The 13C nuclear magnetic resonance (NMR) chemical shifts δc of bridge group carbons (C‐β, C‐α, and C═N) were measured in this work for a wide set of substituted cinnamyl anilines p‐XC6H4CH═CHCH═NC6H4Y‐p (X = NO2, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, CO2Et, Cl, F, H, Me, MeO, or NMe2) and were used to study the substituent effect. In the study on 13C NMR chemical shifts of the titled compounds with single substituent changed, for every bridge carbon δc, the effect of cinnamyl substituent X is opposite to that of aniline substituent Y. That is, the action of the same substituent on different aromatic rings is different from the 13C NMR chemical shifts, and for C‐β, C‐α, and C═N, the choice of correlation equation depends on the ratio ρF(Y)/ρR(Y). When the ratio ρF(Y)/ρR(Y) is close to 1, the chemical shifts of bridge carbons can be well correlated with the single‐parameter equation; otherwise, it is better to adopt the dual‐parameter equation for correlation, and the further the values of ρF(Y)/ρR(Y) stray from 1, the more suitable the corresponding δc values are to be correlated with the dual‐parameter equation. In the study on δc of model compounds with simultaneous variations of substituents X and Y, for δc(C═N), a multi‐parameter correlation equation is obtained, and the substituent cross‐interaction item Δσ2 is suitable to scale the interaction between substituents; however, for δc(C‐α and C‐β), the substituent cross‐interaction item Δσ2 is perhaps too small to be observed. The multi‐parameter correlation equations can be recommended to predict well the corresponding δc values of disubstituted cinnamyl anilines. Copyright © 2012 John Wiley & Sons, Ltd.
dLong-range electronic substituent effects were targeted using the substituent dependence of d C (C═N), and specific cross-interactions were explored extendedly. A wide set of N-(4-X-benzylidene)-4-(4-Y-styryl) anilines, p-X-C 6 H 4 CH═NC 6 H 4 CH═CHC 6 H 4 -p-Y (X = NMe 2 , OMe, Me, H, Cl, F, CN, or NO 2 ; Y = NMe 2 , OMe, Me, H, Cl, or CN) were prepared for this study, and their 13 C NMR chemical shifts d C (C═N) of C═N bonds were measured. The results show that both the inductive and resonance effects of the substituents Y on the d C (C═N) of p-X-C 6 H 4 CH═NC 6 H 4 CH═CHC 6 H 4 -p-Y are less than those of the substituents Y in p-X-C 6 H 4 CH═NC 6 H 4 -p-Y. Moreover, the sensitivity of the electronic character of the C═N function to electron donation/electron withdrawal by the substituent X or Y attenuates as the length of the conjugated chain is elongated. It was confirmed that the substituent cross-interaction is an important factor influencing d C (C═N), not only when both X and Y are varied but also when either X or Y is fixed. The long-range transmission of the specific cross-interaction effects on d C (C═N) decreases with increasing conjugated distance between X and Y. The results of this study suggest that there is a long-range transmission of the substituent effects in p-X-C 6 H 4 CH═NC 6 H 4 CH═CHC 6 H 4 -p-Y. a The values of d C (C═N) M3 were taken from Neuvonen et al. [16] SUBSTITUENT EFFECTS IN BENZYLIDENE ANILINES
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