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A Computational Study on the Photochemistry of 2,4,4‐Trimethyl‐1‐pyrroline 1‐Oxide and Investigation on the Reaction Paths of Its Photoproduct Oxaziridine
Author(s) -
Sen Sindhuja,
Chattopadhyay Anjan
Publication year - 2019
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201903230
Subject(s) - oxaziridine , azetidine , nitrone , chemistry , photochemistry , conical intersection , pyrroline , transition state , stereochemistry , organic chemistry , molecule , cycloaddition , catalysis
Abstract This computational study reveals the reaction pathways of the experimentally reported photo‐conversion of 2,4,4‐trimethyl‐1‐pyrroline 1‐oxide to oxaziridine and the subsequent reactions (thermal and photochemical) of this photo‐product. The latter involve the oxaziridine to N‐acetyl azetidine, pyrrolidone and pyrroline formation paths. The photo‐excitation of the cyclic nitrone gives weakly allowed S 0 ‐S 1 and strongly allowed S 0 ‐S 2 transitions with transition moment values of 0.12 D and 3.16 D, respectively. The low‐lying conical intersection (S 0 /S 1 ) situated at 80 kcal / mol (at CASSCF level) above the ground state nitrone geometry is found to be responsible for the oxaziridine formation. This bicyclic compound has to overcome a barrier (∼ 50 kcal / mol) to form N‐acetyl azetidine. The transition state involved in this process has an imaginary frequency of 909 i cm −1 . A parallel photochemical path has been also predicted for the same reaction. The thermal oxaziridine‐pyrrolidone conversion involves a transition state with an imaginary frequency of 1136 i cm −1 which indicates the breaking of the C–CH 3 bond adjacent to the nitrogen atom. This cyclic amide compound is almost 20–25 kcal/mol more stable than the 4‐membered cyclic azetidine and both are lower in energy than oxaziridine.