Structural determination of carvone, a component of spearmint, by means of gas electron diffraction augmented by theoretical calculations

Abstract

The molecular structure and conformation of carvone, a compound with a minty odor, were investigated by means of gas electron diffraction supported by theoretical calculations. Electron diffraction patterns were recorded by heating the nozzle up to 128 °C to obtain enough scattering intensity. The infrared spectrum was also measured by using an absorption cell with a path length of 10 m. The obtained molecular scattering intensities were analyzed with the aid of theoretical calculations and infrared spectroscopy. It was revealed that the experimental data are well reproduced by assuming that carvone consists of a mixture of three conformers that have the isopropenyl group in the equatorial position and mutually differ in the torsional angle around the single bond connecting the ring and the isopropenyl group. It was also found that the puckering amplitude of the ring of carvone is close to those of menthol and isomenthol, a minty compound and its nonminty isomer. The determined structural parameters ( r g and ∠ α ) of the most abundant conformer of carvone are as follows: 〈 r(C–C)〉=1.520(3) Å; 〈 r(CC)〉=1.360(5) Å; r(CO)=1.225(5) Å; 〈 r(C–H)〉=1.104(4)Å; 〈∠CC–C〉=121.1(5)°; 〈∠C–C–C〉=110.4(5)°; ∠C–CO–C=117.1(14)°; 〈∠C–C–H〉=111.1(13)°. Angle brackets denote average values and parenthesized values are the estimated limits of error (3 σ) referring to the last significant digit.