Analysis of the vibrational spectra of trans-N,N′-bis-salicylidene-1′,2′-cyclohexanediamine tautomers

The vibrational spectra of two tautomeric forms of trans-N,N′-bis-salicylidene cyclohexanediamine (OHN-sal and NHO-sal) as well as the reference compound with weak hydrogen bond (OH-sal) have been analysed using DFT and HF methods. The results have revealed the most important spectroscopic consequences of formation of the medium strength intramolecular OH⋯N hydrogen bond and the proton transfer in Schiff bases. The IR spectrum of OHN-sal calculated by the B3LYP/6-31G(d,p) method is in a satisfactory agreement with the experimental one. The discrepancies result from the neglect of the anharmonicity correction and intermolecular interactions. The HF/6-31G level of theory do not reproduce correctly the intramolecular hydrogen bond in the Schiff base studied.