Borho Nicole, Xu Yunjie
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada.
Phys Chem Chem Phys. 2007 Mar 21;9(11):1324-8. doi: 10.1039/b608561j. Epub 2007 Feb 2.
High resolution spectrum of methyl lactate, a chiral alpha-hydroxyester, has been investigated using a molecular jet Fourier transform microwave spectrometer. High level ab initio calculations were employed to study the conformational isomerism of methyl lactate. The observed rotational spectrum confirms that the most stable conformer has an intramolecular hydrogen bond of OH...O==C type, as predicted by the ab initio calculations. The internal rotation barrier heights of the ester methyl group and the alpha-carbon methyl group were calculated to be 5.4 and 14.5 kJ mol(-1) at the MP2/aug-cc-pVDZ level of theory for the most stable conformer. The internal rotation splittings due to the ester methyl group were observed and analyzed and the ester methyl group tunneling barrier height was determined experimentally to be 4.762 (3) kJ mol(-1).
使用分子束傅里叶变换微波光谱仪研究了手性α-羟基酯乳酸甲酯的高分辨率光谱。采用高水平的从头算计算来研究乳酸甲酯的构象异构现象。观察到的转动光谱证实，最稳定的构象异构体具有从头算计算所预测的OH...O==C型分子内氢键。在MP2/aug-cc-pVDZ理论水平下，对于最稳定的构象异构体，酯甲基和α-碳甲基的内旋转势垒高度分别计算为5.4和14.5 kJ mol(-1)。观察并分析了由酯甲基引起的内旋转分裂，通过实验确定酯甲基隧穿势垒高度为4.762(3) kJ mol(-1)。
