Substituent effects on the stretching vibration frequencies of C=C bridge bond in aryl ethylene with furyl or thienyl group

Abstract

To explore the substituent effects on the stretching vibration frequencies ν C=C of C=C bridge bond in 1-furyl/thienyl-2-aryl ethylene XCH=CHArYs, 60 samples of XCH=CHArYs were synthesized, and their infrared absorption spectra were recorded. The regression analyses between the ν C=C values of XCH=CHArYs and the substituent parameters of X and Y were made in detail. Finally, an optimality equation (shown as Equation 3) quantifying the ν C=C values of XCH=CHArYs was obtained. It shows that the substituent effects on the ν C=C values of XCH=CHArYs mainly reflect in Hammett constant of X and the excited-state substituent constants of X and Y. Among the parameters in Equation (3), the excited-state substituent constant of X contributes the most to the ν C=C values of XCH=CHArYs as seen from the fraction contributions. On the whole, the contribution of X to the ν C=C values of XCH=CHArYs is larger than that of Y.