Computational investigation of oxaziridine photoconversion and E Z isomerization processes of some acyclic nitrone systems

Abstract

Computational and theoretical chemistry have reached new heights due to the advancement in the computing methodologies and facilities in the recent years. Nowadays, comprehensive investigations of the mechanisms of unexplored complicated chemical reactions are possible through computational studies which include detection of short-lived transition states in the reaction path, as well. In the last few decades, behavior of the photo-excited organic molecules and their photochemical reaction pathways are horoughly analyzed by exploring their potential energy surfaces. The radiative and non-radiative decay processes have drawn considerable attention of the computational chemists and their enormous efforts have put forward the explanations of several unanswered questions in photophysics and photochemistry. The huge development in the field of ultrafast non-radiative processes requires a special mention in this regard; they are found to be governed by decay of excited states through radiationless molecular funnels (conical intersections) and their key role in the photochemical reactions of various organic molecules has been widely accepted now. In Chapter 1 of the present thesis, various important points on the potential energy surfaces and the surface crossing phenomenon have been discussed in detail. In this thesis work, our targeted molecules for photochemical investigations are different kinds of acyclic nitrone systems. N-Oxides of imines, commonly known as Nitrones, are well known for their 1,3 dipolar cycloaddition reactions; they are highly photosensitive and on photo-irradiation results in corresponding oxaziridines and other photoproducts, such as amides. The cis-trans isomerizations of nitrones were reported to occur thermally or through triplet excited states, in presence of photosensitizers, whereas, their conversion to oxaziridine were found to be a photochemical process and involvement of singlet excited state was suspected in this reaction. These investigations have revealed the fact that the stability