Determination And Application Of Excited-state Substituent Constants Of Furyl And Thienyl Groups

Six series of styrene derivatives XCH=CHArY containing the styrene parent molecular skeleton were synthesized,here X is furyl or thienyl.Their molecular structures were characterized by nuclear magnetic resonance spectrum(1H NMR,13C NMR).Six excited-state substituent constants σCC(p)ex of groups X were obtained and their application in 13C NMR spectrum(δC(X)、δC(Y)),reduction potential(Ered)and infrared absorption spectrum(vC=C)were investigated.The details are as follows:(1)The UV absorption spectra of 1-furyl/thienyl-2-aryl ethylene were measured in anhydrous ethanol and their wavelength of absorption maximum λmax were recorded.For the wavenumber υmax(cm-1,υmax=1/λmax)of the λmax,a quantitative correlation analysis was performed,and six excited-state substituent constants σCC(p)ex of groups X were obtained by means of curve-fitting method.Taking the υmax values of total 90 compounds of styrene derivatives as one data set(25 compounds of literature and 65 compounds of this work),a quantitative correlation analysis was performed,and the reliability of the obtained σCC(p)ex was verified.In addition,12 samples of disubstituted Schiff bases(XCH=NArY)involving the groups X were synthesized and their υmax values were recorded.Using these 12 υmax values together with the 14 υmax values of Schiff bases taken from reference(total of 26 compounds),we further verified the σCC(p)ex values being reliable by means of quantitative correlation method.(2)The change regularity of the 13C NMR chemical shifts(δC(X)and δC(Y))of the bridging bond C=C for 1-furyl-2-aryl ethylene and 1-thienyl-2-aryl ethylene compounds were investigated,four quantitative regression equations with good results were obtained.Putting 1-furyl-2-aryl ethylene and 1-thienyl-2-aryl ethylene into one data set,two equations were proposed to quantifying the chemical shifts δC(X)and δC(Y)of bridging bond C=C for the furyl/thienyl-CH=CHArY,respectively,in which the difference of furyl and thienyl groups were expressed by an indicator variable(I).The results indicate:the δC(X)and δC(Y)of furyl/thienyl-CH=CHArY are mainly affected by Hammett constant of substituent Y(σ(Y)),excited-state constants of substituent X(σCC(p)ex(X)),where δC(Y)are also affected by the substituent cross-interaction effect between X and Y(σCCex(XY)).The parameter σCC(p)ex(X)plays an important role in quantifying the change regularity of δC(X)and δC(Y)of furyl/thienyl-CH=CHArY(3)The substituent effects on the Ered of XCH=CHArY were explored,and an expression of quantifying the Ered of XCH=CHArY were obtained.Their reduction potentials Ered are mainly affected by Hammett constants of substituent X and Y(σ(p)(X)and σ(Y)),excited-state substituent constants of substituent X and Y(σCC(p)ex(X)and σCCex,(Y)).Among these parameters,the σCC(p)ex(X)has the most contribution to the Ered of XCH=CHArY.The reduction potentials of styrene,stilbenes and Schiff base compounds were compared,the results show that the carbon-carbon double bond of styrene is the most difficult to be reduced,whereas the carbon-nitrogen double bond of Schiff base is easiest to be reduced.(4)The change regularity of the infrared absorption frequency υC=C of the C=C in XCH=CHArY were studied,and a four-parameter quantitative regression equation were obtained.The results show that the υC=C of 1-furyl/thienyl-2-aryl ethylene are mainly affected by Hammett constant of substituent X(σ(p)(X)),excited-state substituent constants of X and Y(σCC(p)ex(X)and σCCex(Y)).In which the σCC(p)ex(X)has the most contribution to the υC=C.