Accuracy of quantum chemistry structures of chiral tag complexes and the assignment of absolute configuration
Accuracy of quantum chemistry structures of chiral tag complexes and the assignment of absolute configuration
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DOI：
10.1039/d2cp04060c
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发表时间：
2022-11-09
影响因子：
3.3
通讯作者：
Pate，Brooks H.
中科院分区：
文献类型：
--
作者：
Mayer，Kevin;West，Channing;Pate，Brooks H.
分子的绝对构型可以通过分析分析物与已知构型的手性小分子络合的分子旋转光谱来确定。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异构体的方法类似于核磁共振(核磁共振)光谱中的手性衍生化。对于旋转手性标记法，衍生化使用非共价相互作用来安装新的手性中心，避免了在使用共价化学时可能导致分析物外消旋的复杂情况。这种方法的实际成功在于能够将指定的旋转光谱归因于在用于将样品引入微波光谱仪的脉冲喷射膨胀中形成的非对映异构体同手性和异手性标记络合物的特定几何形状。对实验旋转光谱的分子结构分配使用量子化学平衡几何来提供表征旋转光谱的光谱参数的理论估计。本文报道了(3)-丁基-2-醇与马鞭草酮形成的络合物的高灵敏度旋转光谱研究结果。归属了四个同手性和四个异手性配合物的转动光谱。此外，其中5个物种的14个不同的、单取代的13C同位素谱在自然丰度中被归属。对这些光谱的分析通过确定碳原子的位置坐标提供了对配合物的直接结构表征。该数据集被用于对手性标记络合物的候选平衡几何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中常用的方法。结果表明，量子化学结构的精确度为观测光谱提供了高置信度的团簇几何赋值。结果，实现了分析物(马鞭草酮)绝对构型的高置信度确定。
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 13C 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.