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Updated: Jun 5, 2025

High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
Published on: October 9, 2020
Coupled methyl internal rotations with intermediate and low torsional barriers in 2,5-dimethylanisole investigated by
Haoyue Sun1, Lynn Ferres2, Isabelle Kleiner1
1Université Paris Cité and Univ Paris Est Créteil, CNRS, LISA, F-75013 Paris, France.
Abstract:
We recorded and analyzed the microwave spectra of 2,5-dimethylanisole using a pulsed molecular jet Fourier transform microwave spectrometer and the newly developed Passage And Resonant-Impulse Synergy spectrometer across a frequency range of 2-26.5 GHz with support from quantum chemical calculations. Only one conformer was predicted and observed, where the methoxy group and its adjacent methyl group adopt anti-positions. The two methyl groups, located at the ortho- and meta-positions of the anisole ring, exhibit internal rotation, resulting in quintet splitting of all rotational transitions. The low torsional barrier of the m-methyl group, amounting to 65.723 611(84) cm-1, combined with the intermediate barrier of 451.664(19) cm-1 for the o-methyl group, presented challenges in the spectral analysis. Using the XIAM and BELGI-Cs-2Tops programs, we successfully fitted 460 torsional intrastate rotational transitions, allowing for precise determination of molecular parameters and internal rotation characteristics. The torsional barriers are compared to those in the related isomers 2,3-, 2,4-, and 3,4-dimethylanisole as well as other o- and m-substituted toluene derivatives.
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