The effect of internal rotation in p-methyl anisole studied by microwave spectroscopy

The Fourier transform microwave spectrum of p-methyl anisole, CH3C6H4OCH3, was measured in the frequency range from 2 to 26.5 GHz under molecular jet conditions. The conformational analysis yielded only one stable conformer, in which all heavy atoms are co-planar, and which was identified after analyzing the spectrum by comparison with the results from quantum chemical calculations. The barrier of the V-3 potential of the ring methyl rotor was found to be 49.6370(1) cm(-1), and was compared with that found in other para-substituted toluenes as well as in o-methyl anisole. A comparison between two theoretical approaches treating internal rotations, the rho axis method (program BELGI-C-s) and combined axis method (program XIAM), was also performed. (c) 2017 Elsevier Inc. All rights reserved.