On the validity of the constants of ionic substituents. Substituent effects on the cyano stretching frequencies and intensities trans-alpha-phenyl-beta-arylacrylonitriles

Fourier-transform IR frequencies v(C drop N) and integrated intensities A(C drop N) of the cyano groups of a series of trans-alpha-phenyl-beta-arylacrylonitriles (51 compounds) have been measured. Both v(C drop N) and the square roots of A(C drop N) of the neutral m- and p-substituted compounds (34 examples) have been found to correlate satisfactorily with sigma(+) substituent constants, as well as according to the equation of Yukawa-Tsuno. Diortho-substituted compounds deviate strongly from the correlation lines because of the steric ortho-effects mainly. sigma(+) (and other) constants of ionic substituents (seven examples) have proved satisfactorily valid in the series studied. The transmission coefficient of the C=C double bond in the series has been estimated to be 0.7.