title: Model study of the photochemical rearrangement pathways of 1,2,4-oxadiazole.
abstract: The mechanisms of photochemical isomerization reactions are investigated theoretically by using a model system of 1,2,4- oxadiazole with the CAS(14,9)/6-311G(d) and MP2-CAS-(14,9)/ 6-311++G(3df,3pd)//CAS(14,9)/6-311G(d) methods. Three reaction pathways are examined, including 1) the direct mechanism, 2) the ring contraction-ring expansion mechanism, and 3) the internal cyclization-isomerization mechanism, which lead to two types of photoisomers. The theoretical findings suggest that conical intersections play a crucial role in the photorearrangement of 1,2,4-oxadiazoles. These model investigations also indicate that the preferred reaction route for 1,2,4-oxadiazole, which leads to phototransposition products, is as follows: reactant → Franck-Condon region → conical intersection → photoproduct. In other words, the direct mechanism is a one-step process that has no barrier. These theoretical results agree with the available experimental observations.
authors.affiliation: Department of Applied Chemistry, National Chiayi University, Chiayi 60004 (Taiwan); Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 80708 (Taiwan). midesu@mail.ncyu.edu.tw.
authors.forename: Ming-Der
authors.initials: MD
authors.lastname: Su
mesh_terms: D008958:Models, Molecular; D015394:Molecular Structure; D010069:Oxadiazoles / Q000737:chemistry*; D055668:Photochemical Processes; D011789:Quantum Theory
chemical_list: D010069:Oxadiazoles
keywords: 1,2,4-oxadiazole; conical intersections; photochemistry; photoisomerization reactions; photorearrangements