Terpenes in the gas phase: The structural conformation of S-(–)-perillaldehyde investigated by microwave spectroscopy and quantum chemical calculations

S-(–)-perillaldehyde (C10H14O) has been characterized in the gas phase using a Fourier transform microwave spectroscopy experiment in a supersonic molecular beam. Two conformers − with the isopropenyl group in the equatorial position − have been detected 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. Our study shows that gas phase spectroscopy is a powerful tool for characterizing monoterpenes.