Khemissi Safa, Ferres Lynn, Nguyen Ha Vinh Lam
Univ Paris Est Créteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France.
Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D-52074 Aachen, Germany.
Molecules. 2025 Mar 7;30(6):1195. doi: 10.3390/molecules30061195.
The microwave spectrum of 3,5-dimethylanisole was recorded using a pulsed molecular jet Fourier transform microwave spectrometer, covering the frequency range from 2.0 to 26.5 GHz. Splittings from internal rotations of the - and --methyl groups were observed, analyzed, and modeled using the and the programs for a data set including 622 rotational lines. The torsional barriers of the - and --methyl groups were determined to be 58.62367(53) cm and 36.28449(69) cm, respectively. The low barriers to internal rotation of both methyl groups posed significant challenges for spectral analysis and modeling. The successful assignment was achieved using combination difference loops and separately fitting the five torsional components. Comparing the torsional barriers observed in various toluene derivatives with methyl groups at -positions supports the assumption that electrostatic effects contribute more significantly than steric effects in the low-barrier cases of aromatic molecules.
使用脉冲分子束傅里叶变换微波光谱仪记录了3,5-二甲基苯甲醚的微波光谱，覆盖频率范围为2.0至26.5 GHz。观察、分析并使用 和 程序对包括622条转动谱线的数据集进行建模，以研究 -甲基和 -甲基的内旋转分裂。确定 -甲基和 -甲基的扭转势垒分别为58.62367(53) cm和36.28449(69) cm。两个甲基的低内旋转势垒给光谱分析和建模带来了重大挑战。通过组合差环并分别拟合五个扭转分量成功完成了谱线归属。将在各种 -位带有甲基的甲苯衍生物中观察到的扭转势垒进行比较，支持了在芳香族分子的低势垒情况下，静电效应比空间效应贡献更显著的假设。
