Conformational relaxation of S-(+)-carvone and R-(+)-limonene studied by microwave Fourier transform spectroscopy and quantum chemical calculations

S-(+)-carvone (CHO, 5-isopropenyl-2- methylcyclohex-2-en-1-one) and R-(+)-limonene (CH, 4-isopropenyl-1-methylcyclohexene) have been characterized in the gas phase using a Fourier transform microwave spectrometer coupled to a supersonic molecular beam. Two conformers - with the isopropenyl group in the equatorial position - have been detected for each compound and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR-Raman-VCD spectra. © 2012 Springer Science+Business Media New York.