Abstract The photoreaction mechanism of 3-chloro-2-hydroxypyridine isolated in a low-temperature argon matrix was investigated by IR spectroscopy and density functional theory (DFT) calculations. Two tautomeric forms, keto and enol I, with an intramolecular N⋯H–O hydrogen bond, existed in the matrix before UV irradiation. Tautomerization from the keto form to enol I occurred completely upon the first UV irradiation ( λ ≥ 300 nm), while the second light irradiation ( λ ≥ 250 nm) induced the reverse tautomerization from enol I to the keto form as well as photodissociation to yield a five-membered-ring ketene, 2 H -pyrrol-2-ylidenemethanone, and HCl. The latter is similar to the photolysis of 2-chlorophenol to yield its corresponding five-membered-ring ketene by Wolff rearrangement after dissociation of HCl by UV irradiation. Kinetic analysis indicates the existence of a short-lifetime precursor, which is expected to be the less stable enol tautomer with an intramolecular Cl⋯H–O hydrogen bond. A trace of the intermediate was spectroscopically detected only during UV irradiation.

中文翻译：

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在 Ar 基质中分离的 3-氯-2-羟基吡啶的光诱导沃尔夫重排和互变异构化

摘要 通过红外光谱和密度泛函理论 (DFT) 计算研究了在低温氩气基质中分离的 3-氯-2-羟基吡啶的光反应机理。在紫外线照射前，基质中存在两种互变异构形式，酮和烯醇 I，具有分子内 N⋯H-O 氢键。从酮形式到烯醇 I 的互变异构完全发生在第一次紫外线照射 (λ≥300 nm) 时，而第二次光照射 (λ≥250 nm) 诱导从烯醇 I 到酮形式的反向互变异构以及光解产生五元环烯酮、2 H-吡咯-2-亚基甲酮和 HCl。后者类似于 2-氯苯酚的光解作用，在紫外线照射下 HCl 解离后，通过沃尔夫重排产生其相应的五元环烯酮。动力学分析表明存在一个短寿命前体，预计它是较不稳定的烯醇互变异构体，具有分子内 Cl⋯H-O 氢键。仅在紫外线照射期间通过光谱法检测到痕量中间体。