Methyl Internal Rotation in the Microwave Spectrum of o-Methyl Anisole.

The microwave spectrum of o-methyl anisole (2-methoxytoluene), CH3OC6H4CH3, has been measured by using a pulsed molecular jet Fourier transform microwave spectrometer operating in the frequency range 2-26.5 GHz. Conformational analysis using quantum chemical calculations at the MP2/6-311 + + G(d,p) level of theory yields only one stable conformer with a C-s structure, which was assigned in the experimental spectrum. A-E splittings due to the internal rotation of the ring methyl group could be resolved and the barrier to internal rotation was determined to be 444.05(41) cm(-1). The experimentally deduced molecular parameters such as rotational and centrifugal distortion constants as well as the torsional barrier of the ring methyl group are in agreement with the calculated values.