FT-IR, FT-Raman, UV–Vis, NMR and structural studies of carquejyl acetate, a distinctive component of the essential oil from Baccharis trimera (less.) DC. (Asteraceae)

Abstract

Carquejyl acetate (CA), the main component of the essential oil from Baccharis trimera was isolated and characterized by using Fourier Transform infrared (FT-IR) and Raman (FT-Raman), Ultraviolet–Visible (UV–Visible), Electronic Circular Dichroism (ECD), Mass, Hydrogen and Carbon Nuclear Magnetic Resonance (1H- and 13C NMR) and 2D 1H-1H gCOSY, 1H-13CgHSQC, 1H-13CgHMBC spectroscopies. Two conformers were found in the potential energy surface (PES) for CA in gas and aqueous solution phases by using the hybrid B3LYP method with the 6-31G* and 6-311++G** basis sets and, only one of them, C2, was the most stable and with higher populations in both phases. Natural bond orbital (NBO) studies evidence the high stability of CA as compared with carquejol while atoms in molecules (AIM) analyses reveals the different characteristics of the H bonds formed showing CA higher topological properties. The gap values suggest that carquejol is most reactive than CA while higher values in the global electrophilicity and nucleophilicity indexes are observed for C2, as compared with carquejol. Very good correlations between the experimental FTIR, FT-Raman, UV–Visible and 1H and 13C NMR spectra with their theoretical counterparts were found. The ECD spectrum predicted for C2 reveals the absolute configuration of CA. The complete assignment of the 84 normal vibration modes of CA is presented.