Mayer Kevin, West Channing, Marshall Frank E, Sedo Galen, Grubbs Garry S, Evangelisti Luca, Pate Brooks H
Department of Chemistry, University of Virginia, 409 McCormick Rd., Charlottesville, VA 22904, USA.
Department of Chemistry, Missouri University of Science and Technology, 142 Schrenk Hall, 400 W. 11th St., Rolla, MO 65409, USA.
Phys Chem Chem Phys. 2022 Nov 23;24(45):27705-27721. doi: 10.1039/d2cp04060c.
The absolute configuration of a molecule can be established by analysis of molecular rotational spectra of the analyte complexed with a small chiral molecule of known configuration. This approach of converting the analyte enantiomers, with identical rotational spectra, into diastereomers that can be distinguished spectroscopically is analogous to chiral derivatization in nuclear magnetic resonance (NMR) spectroscopy. For the rotational chiral tag method, the derivatization uses noncovalent interactions to install the new chiral center and avoids complications due to possible racemization of the analyte when covalent chemistry is used. The practical success of this method rests on the ability to attribute assigned rotational spectra to specific geometries of the diastereomeric homochiral and heterochiral tag complexes formed in the pulsed jet expansion that is used to introduce samples into the microwave spectrometer. The assignment of a molecular structure to an experimental rotational spectrum uses quantum chemistry equilibrium geometries to provide theoretical estimates of the spectrum parameters that characterize the rotational spectrum. This work reports the results of a high-sensitivity rotational spectroscopy study of the complexes formed between (3)-butyn-2-ol and verbenone. The rotational spectra of four homochiral and four heterochiral complexes are assigned. In addition, the 14 distinct, singly-substituted C isotopomer spectra of five of these species are assigned in natural abundance. Analysis of these spectra provides direct structural characterization of the complexes through determination of the carbon atom position coordinates. This data set is used to benchmark quantum chemistry calculations of candidate equilibrium geometries of the chiral tag complexes. The quantum chemistry calculations are limited to methods commonly used in the field of rotational spectroscopy. It is shown that the accuracy of the structures from quantum chemistry provides a high-confidence assignment of cluster geometries to the observed spectra. As a result, a high-confidence determination of the analyte (verbenone) absolute configuration is achieved.
通过分析与已知构型的小手性分子络合的分析物的分子旋转光谱，可以确定分子的绝对构型。这种将具有相同旋转光谱的分析物对映体转化为可通过光谱区分的非对映体的方法类似于核磁共振（NMR）光谱中的手性衍生化。对于旋转手性标签法，衍生化利用非共价相互作用来安装新的手性中心，并避免了使用共价化学时分析物可能发生消旋化带来的复杂性。该方法的实际成功取决于能否将指定的旋转光谱归因于在脉冲喷射膨胀中形成的非对映体纯手性和杂手性标签络合物的特定几何结构，脉冲喷射膨胀用于将样品引入微波光谱仪。将分子结构与实验旋转光谱进行匹配时，使用量子化学平衡几何结构来提供表征旋转光谱的光谱参数的理论估计。这项工作报告了对（3）-丁炔-2-醇和马鞭草烯酮形成的络合物进行高灵敏度旋转光谱研究的结果。确定了四种纯手性和四种杂手性络合物的旋转光谱。此外，还确定了其中五个物种的14种不同的单取代碳同位素异构体光谱的天然丰度。通过确定碳原子位置坐标，对这些光谱的分析提供了络合物的直接结构表征。该数据集用于对映体标签络合物候选平衡几何结构的量子化学计算进行基准测试。量子化学计算仅限于旋转光谱领域常用的方法。结果表明，量子化学结构的准确性为观察到的光谱提供了高可信度的簇几何结构匹配。因此，实现了对分析物（马鞭草烯酮）绝对构型的高可信度测定。
