Theoretical investigations on the structure and vibrational spectra of N-(2-hydroxy-1-naphthylidene)threonine (original) (raw)

Ab initio Hartree±Fock and the hybrid density functional theoretical investigations on the structure and vibrational frequencies of Schiff's base ligand 1-(salicylaldimino)-3-biuret (1) and its anion are carried out by using the Dunning-Huzinaga double zeta basis set. For 1 the syn and anti conformers, both having intramolecular hydrogen bonding, are obtained as the local minima on the potential energy surface. In the syn conformer, the hydrogen bond through nitrogen of imine group results in a formation of a six membered ring which stabilizes this conformer over the anti conformer. The energy difference of the syn and anti conformers from the hybrid density functional theory has been predicted to be 28.09 kJ mol 21 . A comparison of the vibrational spectra of the anion and the syn conformer from the density functional theory predicts that both the 1763 and 1715 cm 21 carbonyl stretching vibrations are up-shifted by ,50 cm 21 on protonation of the anion. Also the new bands at 1576 and 1326 cm 21 assigned to HNH scissoring and strongly coupled CN stretching with CCH rocking, respectively, will appear. The 1326 cm 21 vibration is, however, predicted only for the more stable syn conformer. q 2. Computational method gaussian 94 quantum chemistry package [10] was Journal of Molecular Structure (Theochem) 585 (2002) 159±165 0166-1280/02/$ -see front matter q