Molecular structure, vibrational spectra and HOMO, LUMO analysis of yohimbine hydrochloride by density functional theory and ab initio Hartree–Fock calculations

Yohimbine hydrochloride (YHCl) is an aphrodisiac and promoted for erectile dysfunction, weight loss and depression. The optimized geometry, total energy, potential energy surface and vibrational wavenumbers of yohimbine hydrochloride have been determined using ab initio, Hartree–Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. A complete vibrational assignment is provided for the observed Raman and IR spectra of YHCl. The UV absorption spectrum was examined in ethanol solvent and compared with the calculated one in gas phase as well as in solvent environment (polarizable continuum model, PCM) using TD-DFT/6-31G basis set. These methods are proposed as a tool to be applied in the structural characterization of YHCl. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap are presented.

Graphical abstractIn this work, we report a combined experimental and theoretical study on molecular structure, electronic and vibrational spectra with HOMO–LUMO analysis of a natural product yohimbine hydrochloride (YHCl). Extraction and isolation of YHCl has been performed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► FT-IR and FT-Raman spectra were recorded and compared with the theoretical results. ► The normal modes analysis with PED calculation has been performed. ► The theoretical calculations were made using HF/DFT/B3LYP/6-311++G(d,p) method. ► The absorption spectrum has been compared with the experimental UV–Vis data. ► The calculated HOMO–LUMO transitions with frontier orbital gap are presented.