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

Lynn Ferres; Halima Mouhib; Wolfgang Stahl; Ha Vinh Lam Nguyen

doi:10.1002/cphc.201700276

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

Chemphyschem. 2017 Jul 19;18(14):1855-1859. doi: 10.1002/cphc.201700276. Epub 2017 May 29.

Authors

Lynn Ferres¹, Halima Mouhib^{1

2}, Wolfgang Stahl¹, Ha Vinh Lam Nguyen³

Affiliations

¹ Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074, Aachen, Germany.
² Laboratoire Modélisation et Simulation Multi Echelle (MSME), CNRS UMR 8208, Université Paris-Est, 5, bd. Descartes, 77454, Marne-la-Vallée, France.
³ Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583, Université Paris-Est Créteil, Université Paris Diderot, 61 avenue du Général de Gaulle, 94010, Créteil cedex, France.

PMID: 28481432
DOI: 10.1002/cphc.201700276

Abstract

The microwave spectrum of o-methyl anisole (2-methoxytoluene), CH₃ OC₆ H₄ CH_3, 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.

Keywords: ab initio calculations; internal rotation; microwave spectroscopy; rotational spectroscopy; structure determination.