The mechanism of photoconversion of cyclic dinitrone to oxaziridine and dioxaziridine: A computational investigation of an experimentally reported photochemical reaction

Abstract

The unexplored photochemistry behind the conversion of cyclic dinitrone to oxaziridine and dioxaziridine has been investigated computationally. The mechanism behind the experimentally reported photo‐conversion reaction of 2,2,4,5‐tetramethyl‐2H‐imidazole‐1,3‐dioxide has been analyzed. The allowed S0‐S1 transition in this cyclic dinitrone system is characterized by a transition moment value of 3 Debye. The photo‐excitation to the vertically excited S1 state is subsequently followed by a passage through low‐lying conical intersection(S0/S1). This photoproduct oxaziridine can undergo reverse transformation to the parent dinitrone through a transition state (barrier height 30–40 kcal/mol) with imaginary frequency value close to 1000i cm−1. Under photo‐irradiation, oxaziridine of this dioxide system can undergo strongly allowed singlet‐singlet transition, characterized by HOMO LUMO excitation with transition moment value close to 2.70 Debye. Subsequently, formations of the trans‐ and cis‐dioxaziridines take place through S0/S1 conical intersections.

Revealing the Unexplored Mechanism of Photochemical Oxaziridine Conversion Process of 2H‐imidazole 1‐oxides

“…It can be added here that in the last few decades, several photochemical reactions have been reported where the involvement of CIs have been found [14–35] . In our earlier studies on the cyclic nitrone systems, [11–13] we have studied various pyrroline 1‐oxide and 2H‐imidazole‐1,3‐dioxide systems. There remains huge scope to explore the mechanism of the photochemistry of the substituted 2H‐imidazole 1‐oxide systems.…”

“…In the recent years, our group has been actively involved in the investigations on the photochemistry of nitrones. In addition to the acyclic nitrone systems, in recent years, we have also proposed [10–13] the possible photo‐isomerization mechanisms for most of the above‐mentioned cyclic nitrone systems through quantum mechanical investigations. These studies have indicated that the nitrone to oxaziridine conversion process goes through a low‐lying S 0 /S 1 conical intersection (CI).…”

A computational investigation on the photochemistry of the popular spin‐trap agent N‐tert‐butyl‐α‐phenylnitrone (PBN) and thermal isomerization pathways of its photoproduct oxaziridine

“…During the last 5 years, Chattopadhyay et al [38][39][40][41] have investigated the photo-isomerizations and lactam formations of several cyclic N-oxide systems which include methyl-substituted pyrroline 1-oxides and 2H-imidazole N-oxides. These computational investigations have put forward the explanations of several unanswered questions related to the photochemistry and thermal reactions of these cyclic nitrones and nitrone-like compounds.…”