Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074, Aachen, Germany.
Univ Paris Est Creteil and Université de Paris, CNRS, LISA, 94010, Créteil, France.
Chemphyschem. 2021 Dec 3;22(23):2420-2428. doi: 10.1002/cphc.202100514. Epub 2021 Oct 15.
The microwave spectrum of 2-acetyl-3-methylthiophene (2A3MT) was recorded in the frequency range from 2 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer and could be fully assigned to the anti-conformer of the molecule, while the syn-conformer was not observable. Torsional splittings of all rotational transitions in quintets due to internal rotations of the acetyl methyl and the ring methyl groups were resolved and analyzed, yielding barriers to internal rotation of 306.184(46) cm and 321.813(64) cm , respectively. The rotational and centrifugal distortion constants were determined with high accuracy, and the experimental values are compared to those derived from quantum chemical calculations. The experimentally determined inertial defect supports the conclusion that anti-2A3MT is planar, even though a number of MP2 calculations predicted the contrary.
2-乙酰基-3-甲基噻吩（2A3MT）的微波谱在 2 至 26.5GHz 的频率范围内使用分子喷射傅里叶变换微波光谱仪记录，可完全分配给分子的反式构象，而顺式构象则不可见。由于乙酰甲基和环甲基的内部旋转，五重态中所有旋转跃迁的扭转分裂得到解决和分析，分别得出内部旋转的势垒为 306.184（46）cm 和 321.813（64）cm。旋转和离心扭曲常数被高精度地确定，实验值与量子化学计算得出的值进行了比较。实验确定的惯性缺陷支持反式 2A3MT 是平面的结论，尽管一些 MP2 计算预测了相反的结果。
