IR studies on the validity of constants of ionic substituents in the benzylidenemalononitrile series

Fourier-transform IR frequencies and integrated intensities of the cyano groups of a series of benzylidenemalononitriles (34 compounds) have been measured in dimethyl sulphoxide. Excellent and satisfactory correlations have been found between spectroscopic features and substituent constants, sigma(+) (and other) constants of ionic substituents (three examples) have proved satisfactorily valid in the series studied. The C=C bridge transmits the substituent effects on the intensities twice as strong than the effects of the same substituents on the corresponding frequencies.