Matrix-isolation FT-IR and theoretical investigation of the vibrational properties of the sterically hindered ortho-hydroxy acylaromatic Schiff bases

FT-IR and FT-Raman spectra of the ortho-hydroxy acylaromatic Schiff bases (2-(α-(N-methylimino)ethyl)-4-chloro-6-nitrophenol – I, 2-(α-(N-methylimino)ethyl)-4,6-dichlorophenol – II), and their isotoposubstitutions have been recorded in the range of 4000–50 cm−1. The spectra were interpreted by a normal coordinate analysis based on B3LYP/6-31++G(d,p) density functional calculations and experimental deuterosubstitution. Proton transfer equilibrium between the enolic and keto tautomers of two sterically hindered Schiff bases has been studied combined experimental (FT-IR matrix-isolation and FT-Raman) and theoretical (DFT/B3LYP/6-31++G(d,p)) methods.