Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583, Université Paris-Est Créteil, Université de Paris, Institut Pierre Simon Laplace, 61 avenue du Général de Gaulle, 94010, Créteil cedex, France.
Institut für Physikalische Chemie und Elektrochemie, Lehrgebiet A, Callinstrasse 3a, 30167, Hannover, Germany.
Chemphyschem. 2020 Jun 16;21(12):1243-1248. doi: 10.1002/cphc.202000234. Epub 2020 May 28.
The microwave spectra of the natural substance coumarin, a planar aromatic molecule with the specific scent of maibowle, a popular fruit punch served in spring and early summer, were recorded using a molecular jet Fourier transform microwave spectrometer working in the frequency range from 4.0 to 26.5 GHz. The rotational constants and centrifugal distortion constants were determined with high precision, reproducing the spectra to experimental accuracy. The spectra of all singly-substituted C and O isotopologues were observed in their natural abundances to determine the experimental heavy atom substitution r and semi-experimental equilibrium r structures. The experimental bond lengths and bond angles were compared to those obtained from quantum chemical calculations and those of related molecules reported in the literature with benzene as the prototype. The alternation of the C-C bond lengths to the value of 1.39 Å found for benzene reflects the localization of π electrons in coumarin, where the benzene ring and the lactone-like chain -CH=CH-(C=O)-O- are fused. The large, negative inertial defect of coumarin is consistent with out-of-plane vibrations of the fused rings.
使用工作频率范围为 4.0 至 26.5GHz 的分子喷射傅里叶变换微波光谱仪，记录了天然物质香豆素的微波光谱，香豆素是一种平面芳香分子，具有迈波勒（一种在春季和初夏流行的水果潘趣酒）的特殊香气。使用高精度确定了转动常数和离心畸变常数，重现了实验精度的光谱。观察了所有单取代的 C 和 O 同位素的光谱，以确定实验重原子取代 r 和半实验平衡 r 结构。将实验键长和键角与从量子化学计算以及文献中以苯为原型的相关分子中获得的那些进行了比较。C-C 键长交替到苯中发现的 1.39Å 值反映了香豆素中π电子的定位，其中苯环和内酯链 -CH=CH-(C=O)-O- 融合在一起。香豆素的大的、负的惯性缺陷与融合环的面外振动一致。
