Góbi Sándor, Keresztes Barbara, Schneiker Anita, Tarczay György
Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, H-1518 Budapest, Hungary.
MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, H-1518 Budapest, Hungary.
Phys Chem Chem Phys. 2024 Aug 14;26(32):21589-21597. doi: 10.1039/d4cp02400a.
TA has been isolated in low-temperature -H matrices and it has been exposed to H atoms. In accordance with previous experimental results, TA exclusively exists in its more stable thione tautomeric form in the freshly deposited matrix. However, upon H atom generation, the bands belonging to the precursor start decreasing with the simultaneous appearance of new bands. By comparing the position of these new peaks with earlier results obtained in -H, they can be undoubtedly attributed to the presence of the higher-energy thiol tautomeric forms of TA. No other products could be observed, except for NH. Quantum-chemical computations have been invoked to understand the mechanism behind the observed thione-thiol tautomerization assisted by H atoms. Accordingly, tautomerization starts with barrierless H-atom addition on the S atom of the thione resulting in the formation of the intermediate 1-amino-1-mercapto-ethyl radical (HC-Ċ(-SH)-NH), which has been detected tentatively for the first time. The second step is a barrierless H-atom induced H-abstraction from the -NH moiety of the HC-Ċ(-SH)-NH radical. A comprehensive mechanism for tautomerization is proposed based on the experimental and theoretical results. Although earlier studies showed the possibility of TA thione-thiol tautomerization in cryogenic matrices achieved by energetic UV irradiation, the present study points out that this can also take place through a barrierless pathway by simply exposing the TA molecules to H atoms. As such, this is the first evidence for the occurrence of such a reaction in a matrix-isolated environment. The current results also help us better understand the mystery behind thione-thiol tautomerization in low-temperature environments.
硫代乙酰亚胺（TA）已在低温-H基质中分离出来，并已暴露于氢原子中。根据先前的实验结果，TA在刚沉积的基质中仅以其更稳定的硫酮互变异构形式存在。然而，在产生氢原子后，属于前体的谱带开始下降，同时出现新的谱带。通过将这些新峰的位置与在-H中获得的早期结果进行比较，可以毫无疑问地将它们归因于TA的高能硫醇互变异构形式的存在。除了NH之外，未观察到其他产物。已调用量子化学计算来理解氢原子辅助的硫酮-硫醇互变异构背后的机制。因此，互变异构从硫酮的S原子上无势垒地加成氢原子开始，导致形成中间体1-氨基-1-巯基-乙基自由基（HC-Ċ(-SH)-NH），这是首次初步检测到。第二步是氢原子诱导从HC-Ċ(-SH)-NH自由基的-NH部分无势垒地夺取氢原子。基于实验和理论结果，提出了一个全面的互变异构机制。尽管早期研究表明通过高能紫外线照射在低温基质中TA硫酮-硫醇互变异构是可能的，但本研究指出，通过简单地将TA分子暴露于氢原子，这也可以通过无势垒途径发生。因此，这是在基质隔离环境中发生这种反应的第一个证据。目前的结果也有助于我们更好地理解低温环境中硫酮-硫醇互变异构背后的奥秘。
