A spectroscopic study of the solvent dependent processes of the anils of benzaldehyde and salicylaldehyde

Abstract

The ultraviolet–visible, infrared, and Raman spectral characteristics of some anils of benzaldehyde and salicylaldehyde in several solvents have been investigated. The ultraviolet–visible absorption data indicate that in solvents with a proton donating ability less than or equal to trifluoroethanol a single equilibrium exists in solutions of N-(2-hydroxybenzylidene)aniline, whereas in solvents with a proton donating ability equal to or greater than hexafluoroisopropanol more than one equilibrium occurs. The infrared spectra of this compound dissolved in trifluoroethanol do not show new absorption bands in the 1700–1500 cm−1 region; however, new absorption bands in this region do appear when hexafluoroisopropanol is employed as solvent. From these data it is inferred that the first equilibrium involves the breaking of the chelate hydrogen bond and the second equilibrium involves actual protonation of N-(2-hydroxybenzylidene)aniline in the electronic ground state. A comparison of the infrared and Raman spectra of the title compounds is also made and alternate assignments for several observed bands in the 1700–1500 cm−1 region are proposed.