Reversed substituent effect on C=O stretching vibrations in hydantoin derivatives

Abstract

The infrared spectra have been recorded for thirteen 3-substituted-5,5-dimethylhydantoins in the region of fundamental C=O stretching vibrations in dichloromethane. The frequencies of symmetric and asymmetric C=O stretching vibrations are correlated with Taft's sigma* substituent constants. When the electron-releasing substituents are in position-3 in the hydantoin ring the stretching frequency increases with the increase in the electronegativity. However, the effect of electron-withdrawing substituents appears to be quite opposite, i.e. the carbonyl stretching vibrations are decreased. The correlations with extended Hammett equation Q(x) = alpha sigma(1) + beta sigma(R) + h and with Swain-Lupton equation p(ij) = fF + rR + h give the results which according to Jaffe can be considered as poor. The correlation obtained from Hammett sigma(p) constants furnish satisfacory results except the substituents with a wide range of polarity. The mechanism of the transmission of substituent effects in hydantoin systems is discussed considering the results of above mentioned observations.