Influence Of Substituent Effects On The UV Spectra And Reduction Potential Properties Of N-Phenyl-?-Phenylnitrones

In this work,53 samples of disubstituted N-phenyl-?-phenylnitrones XArCH=N(O)ArY (XPNY) were synthesized, and their molecular structures were confirmed by NMR method. The 1HNMR chemical shifts ?H(CH=N(O)) of CH=N(O) bridging group were identified. The UV absorption spectra of the target compounds were measured in anhydrous ethanol, and their wavelength of the absorption maximum ?max (nm) and their energies vmax (cm-1, vmax=1/?max) were determined; the reduction potential Ered of target compounds were measured by cyclic voltammetry (CV) in [(n-Bu)4NPF6/CH3CN]. The effects of substituents on vmax, Ered and ?H(CH=N(O)) for target compounds were investigated by using the method of quantitative structure-property relationship. The work and the main results are as follows:(1) The influences of substituent effects on the regularities of the UV absorption energy vmax (cm-1, vmax=1/?max) for XPNY were investigated, and a five-parameter equation was established. It was compared with the vmax that were influenced by substituent effects of N-(phenyl-ethylene)-anilines (XPEAY) and N-(benzylidene)-anilines (XBAY). The results indicate: There are no good linear relationships between the vmax of XBAY and XPEAY or XPNY; In case of a same set of X-Y group couples, the distribution of ?max of XPEAY is larger than that of XPNY; The side-group CH3 on the C=N bridging group makes the effect of ?(X) for substituent X larger than that of ?(Y) for substituent Y on the vmax of XPEAY, whereas the O atom makes the effect of ?(Y) larger than that of ?(X) on the vmax of XPNY; The cross-interaction between X and Y has important effect on the vmax of three compounds, however, the cross-interaction between CH3 and X/Y has not important effect on the vmax of XPEAY and the cross-interaction between O and X/Y has not important effect on the vmax of XPNY.(2)The influences of substituent effects on their Ered were investigated, and a three-parameter quantitative equation was established. The differences of substituent effects on the Ered for XPNY versus XBAY and XPNY versus XPEAY were systematically compared.The results indicate: There are no linear relationship among the Ered for XPNY versus XBAY and XPNY versus XPEAY compounds, namely their Ered have own change regularity respectively;The excited-state substituent effect of X group and the indicating parameter of meta-position group have important contribution to the Ered of XPEAY and XBAY,but little to the Ered of XPNY; The excited-state substituent effect of Y group has some contribution to the Ered of XPNY,but rarely to the Ered of XPEAY and XBAY,and can be ignored:The parents of XBAY and XPNY have similar reduction potential, but the parent of XPEAY has lower reduction potential than these of XBAY and XPNY do,and is more difficult to be reduced.(3)The substituent effects on the 1HNMR chemical shifts ?H(CH-N(O)) of CH=N(O)bridging group for XPNY were quantitatively investigated,and a four-parameter quantitative equation was established through optimizati-on.The results indicate:their ?H(CH-N(O))are mainly affected by inductive effect of substituent X (?F(X)),the conj ugative effect of substituent Y (?-R(Y)),the substituent specific cross-interaction effect between X and Y (??-2) and the substituent specific cross-interaction effect between X and O-(??2(X-O-)).Through the compari son of the ?H(CH=N(O)) with the ?H(CH=N) of XBAY,we ob served that the sub stituent effects on the change regularities of 1HNMR chemical shifts for these two kinds of compounds XPNY and XBAY are quite different. In XPNY, the influences of the electronic effects of the X and Y groups on the ?H(CH=N(0)) were severely weakened due to the effect of the O atom on the CH=N(O) bridging bond, and the major factors were translated to the cross-interaction effect between X and O-.