Rostkowska Hanna, Lapinski Leszek, Nowak Maciej J
Institute of Physics, Polish Academy of Sciences , Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
J Phys Chem A. 2017 Sep 21;121(37):6932-6941. doi: 10.1021/acs.jpca.7b05621. Epub 2017 Sep 12.
The UV-induced thione → thiol phototautomeric reaction has been studied for monomeric 3-thio-1,2,4-triazole (3-ST) isolated in low-temperature Ar and n-H (normal hydrogen) matrixes. Prior to any UV irradiation, monomers of 3-ST isolated in solid Ar or solid n-H adopted mainly the most stable thione tautomeric form, as revealed by the IR spectra. Upon UV (λ > 275 nm) irradiation of 3-ST isolated in Ar matrixes, the IR bands due to this thione form decreased, while a set of initially weak bands increased in intensity. Growing bands indicated generation of a photoproduct, which was identified as the thiol tautomer with labile hydrogen atoms attached to sulfur and N(2) atoms. The UV-induced spectral changes allowed also identification of another minor thiol tautomer of 3-ST, which was present in the matrix prior to any irradiation and did not change its population upon exposure to UV light. The identification of the observed isomeric forms was supported by comparison of their separated experimental IR spectra with the spectra theoretically predicted for the various structures of 3-ST. The thione → thiol phototautomerization that was the main UV-induced process observed for 3-ST in Ar matrixes did not occur for monomers of the compound trapped in solid n-H.
已对低温氩气和正氢（普通氢）基质中分离出的单体3-硫代-1,2,4-三唑（3-ST）的紫外线诱导硫酮→硫醇光互变异构反应进行了研究。红外光谱显示，在任何紫外线照射之前，固体氩气或固体正氢中分离出的3-ST单体主要采用最稳定的硫酮互变异构形式。在对氩气基质中分离出的3-ST进行紫外线（λ>275nm）照射时，硫酮形式的红外波段减弱，而一组最初较弱的波段强度增加。不断增强的波段表明生成了一种光产物，该光产物被鉴定为硫醇互变异构体，其硫原子和N(2)原子上连接有不稳定的氢原子。紫外线诱导的光谱变化还可以鉴定出3-ST的另一种次要硫醇互变异构体，该异构体在任何照射之前就存在于基质中，并且在暴露于紫外光后其数量没有变化。通过将观察到的异构体形式的分离实验红外光谱与3-ST各种结构的理论预测光谱进行比较，支持了对观察到的异构体形式的鉴定。对于捕获在固体正氢中的该化合物单体，在氩气基质中观察到的主要紫外线诱导过程——硫酮→硫醇光互变异构化并未发生。
