Ab Initio Molecular Orbital Studies on the Chemiluminescence of 1,2-Dioxetanes

Abstract

The mechanism of chemiluminescence of 1,2-dioxetane (DO) and 3,3,4,4-tetramethyl-1,2-dioxetane (TMDO) are investigated by the ab initio molecular orbital calculation. The rate-determining step of the chemiluminescent reaction is the O−O bond breaking to form the biradicals. The potential energies along the reaction path are calculated by uB3LYP and uB3P86 methods with 6-31+G(d); the calculated potential barriers are in reasonable agreement with experimental activation energies. An overview of the potential surfaces for overall reaction is obtained. The intersystem crossing mechanism from the singlet biradical to the triplet state is investigated, and the reaction path is followed to the 3(nπ*) excited states of the carbonyl group of respective fragment molecules. The mechanism of promotion to the 1(nπ*) excited state of formaldehyde is investigated by the MCSCF method on DO. The reaction rates and the yield of chemiluminescence are discussed by the RRKM theory of unimolecular reaction.

Theoretical studies on thermal stability of alkyl-substituted 1,2-dioxetanes

“…2,7,13,15 Most attempts on mechanistic analysis of this process focused on the question whether the O-O and C-C bond cleavage occurs concertedly or in a stepwise manner. 1,[12][13][14][16][17][18] Theoretical evidence reported so far indicates that the C-C bond stretches along the reaction coordinate, which is consistent with the intuitively assessed merged dioxetane cleavage mechanism, which predicts the concerted, although not simultaneous, cleavage of the O-O and C-C bonds, with the elongation of the O-O bond being more advanced than that of the C-C-bond (concerted biradicallike mechanism). 19,20 This mechanism was first proposed by Adam and used to rationalize both thermal stability and singlet/triplet quantum yields in the series of methyl-substituted 1,2-dioxetanes, including the parent 1,2-dioxetane.…”

“…However, X-ray structural data of these simpler derivatives are not available and theoretical bond distances, angles and dihedral angles are very often compared with that of much more stable 1,2-dioxetanes (see Table S4). [12][13][14]16,17,30 In other words, there are no experimental data concerning the structure of less stable 1,2-dioxetanes and, therefore, it is impossible to assign unequivocally the more adequate theoretical method to access the optimized geometry. In order to adequately compare structural parameters predicted by different methods with experimental values, the geometry of the derivative 30 was optimized by AM1, PM3, HF/6-31G(d) and B3LYP/6-31G(d) methods and the results evaluated with that obtained by X-ray diffraction (Table 3).…”

“…More recently, most of research on the mechanism of excited state formation in thermal cleavage of 1,2-dioxetanes has been carried out by quantum chemical calculations. [12][13][14] However, up to now, no definitive explanation for the chemiexcitation mechanism in 1,2-dioxetane thermolysis was obtained, neither by experimental nor theoretical means. 2,7,13,15 Most attempts on mechanistic analysis of this process focused on the question whether the O-O and C-C bond cleavage occurs concertedly or in a stepwise manner.…”

Theoretical Study of the Reaction of Vitamin B6 with 1O2

“…The presence of open-(diradical) as well as closedshell (zwitterionic-like) solutions for singlet-oxygen species have been discussed in great detail elsewhere. [26,27] In the current work, only closed-shell solutions were found, despite numerous attempts to also locate open-shell species.…”

Luz: um raro produto de reação

“…[16][17][18][19]22,34,35,[48][49][50][51] Além disso, a maioria dos cálculos semiempíricos e ab initio foram realizados tendo o mecanismo birradicalar como base. [52][53][54][55][56][57][58][59][60] Logo, mesmo que a maioria dos cálculos reportados tenha sucesso em explicar os parâmetros de ativação da decomposição de 1,2-dioxetanos, até onde se sabe, nenhum mecanismo geral definitivo foi proposto para racionalizar os valores observados de rendimentos quânticos. 46,61 Recentemente, nosso grupo de pesquisa efetuou cálcu-los teóricos da estrutura de trinta derivados de 4 contendo substituintes alquila, otimizando-se a estrutura dos mesmos por diferentes métodos semiempíricos e ab initio.…”