Hydrogen bonding and substituent group effects in phénols. Part I. Apparent dipole moments and infrared spectra of N-(4-hydroxybenzylidene)-4-substituted-anilines in benzene, carbon tetrachloride, and dioxan

Abstract

Apparent dipole moments in benzene and dioxan of benzylideneaniline and its two para-methyl derivatives have been determined, and used to obtain the inclination of the resultant moment to the N–C(ring) axis in each solvent. The moments in dioxan of 4-hydroxystilbene and 13 N-(4-hydroxybenzylidene)-4-substituted anilines are reported together with hydroxy-group stretching frequencies ν(OH) in carbon tetrachloride and dioxan. To explain the observed moments in dioxan, values of hydroxy-group bond moments µ(O–H) have been calculated. Both ν(OH) and µ(O–H) are found to be linearly related to the Hammett substituent constant, σ. The relative frequency shift in dioxan being adopted as a measure of the enthalpy change on solute–solvent association, these results provide another illustration of the dependence of µ(O–H) on the strength of hydrogen bonding.