The Smell of Coffee: The Carbon Atom Microwave Structure of Coffee Furanone Validated by Quantum Chemistry

The rotational spectra of coffee furanone (2-methyltetrahydrofuran-3-one) have been measured in the frequency range from 2.0 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer. Quantum chemical calculations used for the conformational analysis yielded two stable twist conformers, which were described using the Cremer-Pople notation for five-membered rings. The experimental spectrum of the more stable conformer with the methyl group in equatorial position was assigned and fitted using a rigid rotor model with centrifugal distortion corrections. The spectra of all five C-13-isotopologues could be observed in natural abundance. The carbon atom structure was experimentally deduced using Kraitchman's equations and compared with the structure calculated by quantum chemistry.