Góbi Sándor, Nunes Cláudio M, Reva Igor, Tarczay György, Fausto Rui
CQC, Department of Chemistry, University of Coimbra, 3004-535, Coimbra, Portugal.
Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, H-1518 Budapest, Hungary and MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, Eötvös Loránd University, H-1518 Budapest, Hungary.
Phys Chem Chem Phys. 2019 Aug 21;21(31):17063-17071. doi: 10.1039/c9cp03417j. Epub 2019 Jul 5.
Rotamerization of a hydroxyl (O-H) group by tunneling is well-known and has been extensively studied. On the other hand, similar tunneling processes for the thiol (S-H) group have not been reported yet. In this work, the imino-thiol forms of thioacetamide were studied in cryogenic matrices (Ar, Xe) after UV-irradiation of the common amino-thione form of the compound. Four different imino-thiol forms were generated, corresponding to the cis or trans thiol (C/T) conformers of the two imino isomers (syn and anti; s/a). Noteworthy, the syn-cis (sC) imino-thiol form was found to convert spontaneously to the syn-trans (sT) form (with a half-life of 80 min), in a process whose reaction rate is independent of the temperature (i.e., at 11 or 20 K). Such conformational transformation represents the first experimental observation of an S-H rotamerization occurring by tunneling. Computations based on the Wentzel-Kramers-Brillouin formalism predict a tunneling half-life for the S-H rotamerization of syn-imino sC to sT on the time scale of minutes, in agreement with the experimental observations.
通过隧穿实现的羟基（O-H）基团的旋转异构化是众所周知的，并且已经得到了广泛研究。另一方面，尚未有关于硫醇（S-H）基团类似隧穿过程的报道。在这项工作中，在对该化合物常见的氨基硫酮形式进行紫外线照射后，在低温基质（氩气、氙气）中研究了硫代乙酰胺的亚氨基硫醇形式。产生了四种不同的亚氨基硫醇形式，对应于两种亚氨基异构体（顺式和反式；s/a）的顺式或反式硫醇（C/T）构象异构体。值得注意的是，发现顺式（sC）亚氨基硫醇形式会自发地转化为反式（sT）形式（半衰期为80分钟），该过程的反应速率与温度无关（即，在11K或20K时）。这种构象转变代表了通过隧穿发生的S-H旋转异构化的首次实验观察。基于温策尔-克拉默斯-布里渊形式主义的计算预测，顺式亚氨基sC到sT的S-H旋转异构化的隧穿半衰期在分钟时间尺度上，与实验观察结果一致。
