Gerbig Dennis, Schreiner Peter R
Institute of Organic Chemistry, Justus-Liebig-University , Heinrich-Buff-Ring 58, 35392 Giessen, Germany.
J Phys Chem B. 2015 Jan 22;119(3):693-703. doi: 10.1021/jp503633m. Epub 2014 Jun 18.
Quantum mechanical tunneling governs the C-O bond rotamerization of simple alkyl and aryl carboxylic acid conformers at cryogenic temperatures. In this study, we report tunneling investigations on a series of electronically different α-ketocarboxylic acids including glyoxylic, pyruvic, cyclopropylglyoxylic, and phenylglyoxylic acid in solid Ar and Ne as host materials at temperatures ranging from 3 to 20 K. The higher-lying rotamers generated through photoirradiation with wavelengths of λ = 313 nm or λ > 850 nm convert to their low-energy conformers through hydrogen-tunneling, as evident from the time evolution of their infrared spectra, and the complete suppression of this process by deuteration. The conversion rates sensitively depend on the choice of matrix material and the tunneling half-lives range from a few hours to several days and are higher in Ne than in Ar for glyoxylic, pyruvic, and cyclopropylglyoxylic acid. The advent of tunneling in α-ketocarboxylic acids dominates their conformational preferences and conceivably also the reactivity of biologically and pharmacologically relevant acid congeners.
在低温下，量子力学隧穿控制着简单烷基和芳基羧酸构象异构体的C-O键旋转异构化。在本研究中，我们报道了在3至20K的温度范围内，以固体氩和氖作为主体材料，对一系列电子性质不同的α-酮羧酸（包括乙醛酸、丙酮酸、环丙基乙醛酸和苯乙醛酸）进行的隧穿研究。通过波长为λ = 313nm或λ > 850nm的光照射产生的高能旋转异构体通过氢隧穿转化为低能构象异构体，这从它们的红外光谱随时间的变化以及氘代对该过程的完全抑制中可以明显看出。转化率敏感地取决于基质材料的选择，隧穿半衰期从几小时到几天不等，对于乙醛酸、丙酮酸和环丙基乙醛酸，在氖中的半衰期比在氩中更高。α-酮羧酸中隧穿的出现主导了它们的构象偏好，并且可以想象也主导了与生物学和药理学相关的酸同系物的反应性。
