title: Vibrational circular dichroism and theoretical study of the conformational equilibrium in (-)-S-nicotine.
abstract: We report an extensive study of the molecular and electronic structure of (-)-S-nicotine, to deduce the phenomenon that controls its conformational equilibrium and to solve its solution-state conformer population. Density functional theory, ab initio, and molecular mechanics calculations were used together with vibrational circular dichroism (VCD) and Fourier transform infrared spectroscopies. Calculations and experiments in solution show that the structure and the conformational energy profile of (-)-S-nicotine are not strongly dependent on the medium, thus suggesting that the conformational equilibrium is dominated by hyperconjugative interactions rather than repulsive electronic effects. The analysis of the first recorded VCD spectra of (-)-S-nicotine confirmed the presence of two main conformers at room temperature. Our results provide further evidence of the hypersensitivity of vibrational optical activity spectroscopies to the three-dimensional structure of chiral samples and prove their suitability for the elucidation of solution-state conformer distribution.
authors.affiliation: Department of Physical and Analytical Chemistry, University of Jaén, 23071 Jaén (Spain).
authors.forename: Pilar Gema Rodríguez
authors.initials: PG
authors.lastname: Ortega
authors.forename: Manuel
authors.initials: M
authors.lastname: Montejo
authors.forename: Juan Jesus López
authors.initials: JJ
authors.lastname: González
mesh_terms: D002251:Carbon Tetrachloride / Q000737:chemistry; D002942:Circular Dichroism; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D008962:Models, Theoretical; D008968:Molecular Conformation; D009538:Nicotine / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism
chemical_list: D009538:Nicotine; D002251:Carbon Tetrachloride; D004121:Dimethyl Sulfoxide
keywords: IR spectroscopy; circular dichroism; conformation analysis; density functional calculations; tobacco alkaloids