Conformational Flexibility of Limonene Oxide Studied By Microwave Spectroscopy

Abstract

Monoterpenoids are biogenic volatile organic compounds (BVOCs) that play a major role in atmospheric chemistry, participating in the formation of aerosols. In this work, the monoterpenoid R-(+)-limonene oxide (C10H16O) has been characterized in the gas phase by Fourier transform microwave spectroscopy in a supersonic jet. Five conformers of limonene oxide, four equatorial and one axial considering the configuration of the isopropenyl group, have been unambiguously identified from the analysis of the rotational spectrum. The observed conformers include cis and trans forms, and are stabilised by a subtle balance of hydrogen bonds, dispersive interactions and steric effects. Estimated conformational relative abundances surprisingly reveal that the axial conformer has an abundance similar to some equatorial conformers. In addition, the potential energy surface was extensively explored using density functional theory and ab initio methods.