Optimization of synephrine and its vibrational and electronic structures

Abstract

The optimization of isolated synephrine molecule and its HCl cluster was performed. The potential energy scanning with respect to some dihedral angles at ethylamine side chain was also performed which prefers twelve different low energy structures of single synephrine molecule. The effect of N..H hydrogen bond on geometry and vibrational properties of synephrine in the least energy conformer was studied. The vibrational and electronic structures of all the twelve conformers of synephrine were computed. The experimental FTIR and Raman spectra of synephrine were also recorded in the spectral region 4000–400 cm−1 and 3200-50 cm−1 respectively and correlated with the theoretical spectra of energetically most preferred structure of synephrine. The normal coordinate analysis was employed to scale the overestimated DFT frequencies and to calculate potential energy distributions of vibrtional modes of synephrine. The natural bond orbital analysis was also performed to obtain bond energies and occupancies, HOMO-LUMO and hybridization.