Ferres Lynn, Cheung Jenny, Stahl Wolfgang, Nguyen Ha Vinh Lam
Institute of Physical Chemistry , RWTH Aachen University , Landoltweg 2 , 52074 Aachen , Germany.
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583 , Université Paris-Est Créteil, Université Paris Diderot, Institut Pierre Simon Laplace , 61 avenue du Général de Gaulle , 94010 Créteil Cedex, France.
J Phys Chem A. 2019 Apr 25;123(16):3497-3503. doi: 10.1021/acs.jpca.9b00029. Epub 2019 Feb 26.
The microwave spectrum of 3,4-dimethylanisole, a molecule containing three methyl groups allowing for internal rotation, was recorded using a pulsed molecular jet Fourier transform microwave spectrometer operating in the frequency range from 2.0 to 26.5 GHz. Quantum chemical calculations yielded two conformers with an anti and a syn configuration of the methoxy group, both of which were assigned in the experimental spectrum. Torsional splittings due to the internal rotations of two methyl groups attached to the aromatic ring were resolved and analyzed. The rotational-torsional transitions could be reproduced to measurement accuracy, yielding well-determined rotational and internal rotation parameters. The torsional barriers of the methyl groups at the meta and para position were deduced to be 430.00(37) and 467.90(17) cm, respectively, for the syn-conformer. The respective values for the anti-conformer are 499.64(26) and 533.54(22) cm. A labeling scheme for the G group written as the semidirect product ( C ⊗ C ) (× C was introduced.
3,4-二甲基苯甲醚是一种含有三个可进行内旋转甲基的分子，利用在2.0至26.5 GHz频率范围内工作的脉冲分子束傅里叶变换微波光谱仪记录了其微波光谱。量子化学计算得出了两种构象体，其甲氧基分别为反式和顺式构型，二者均在实验光谱中得到了归属。对与芳环相连的两个甲基内旋转所导致的扭转分裂进行了解析和分析。转动-扭转跃迁能够被重现至测量精度，从而得到了确定良好的转动和内旋转参数。对于顺式构象体，间位和对位甲基的扭转势垒分别推导为430.00(37)和467.90(17)厘米。反式构象体的相应值分别为499.64(26)和533.54(22)厘米。引入了一种将G群表示为半直积(C⊗C)(×C的标记方案。
