Interplay Between Microwave Spectroscopy and X-ray Diffraction: The Molecular Structure and Large Amplitude Motions...

To determine the structural properties of 2,3-dimethylanisole, a multidisciplinary approach was carried out where gas phase rotational spectroscopy recording a spectrum from 2 to 26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer was combined with solid-state X-ray diffraction. Both methods revealed that only one conformer with a planar heavy-atom structure exists. In the solid state, the packing in the monoclinic space group is P2₁ /n with Z=4. In the gas phase spectrum, torsional splittings due to the internal rotations of two methyl groups attached to the phenyl ring were resolved and analyzed, providing an estimate of the barriers to methyl internal rotation of V₃ =26.9047(5) and 518.7(12) cm^-1 for the methyl groups at the ortho- and meta-position, respectively. The coupling between the two internal rotations is modeled on a two-dimensional potential energy surface, which was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory.