EFFECT OF INTRAMOLECULAR DISPERSION INTERACTIONS ON THE CONFORMATIONAL PREFERENCES OF MONOTERPENOIDS

Abstract

The rotational spectra of several monoterpenoids have been reinvestigated with a 2-8 GHz chirped pulse FTMW spectrometer. Axial conformers, in addition to previously reported equatorial conformersfootnote{J. R. Avilés Moreno, F. Partal Ureña, J. J. López González and T. R. Huet, Chem. Phys. Lett., 2009, 473, 17–20.}$^,$footnote{J. R. Avilés Moreno, T. R. Huet and J. J. López González, Struct. Chem., 2013, 24, 1163–1170.}, have been detected for carvone, perillaldehyde, and limonene. Observation of the $^{13}$C isotopologues of these monoterpenoids in their natural abundances allowed the determination of r$_s$ and r$_0$ structures. Axial conformers are stabilised by dispersion interactions between the six-membered ring of the monoterpenoids and the isopropenyl group. Comparison of experimental data with ab initio and density functional calculations shows that an accurate description of dispersion interactions is still a challenge for theoretical methods. _x000d_