CAS MCSCF/CAS MCQDPT2 Study of the Mechanism of Singlet Oxygen Addition to 1,3-Butadiene and Benzene

Abstract

The 1,4-cycloaddition reactions of the singlet (1Δg) oxygen with s-cis-1,3-butadiene and benzene, with the formation of 3,6-dihydro[1,2]dioxin and 2,3-dioxabicyclo[2.2.2]octa-5,7-diene, respectively, were studied by means of the CAS MCSCF/CAS MCQDPT2 ab initio method with the 6-31G* basis set. In the case of butadiene the reaction was found to be exoenergetic and the product was found to have C 2 symmetry, with the peroxide moiety in the gauche configuration. In the case of benzene the reaction was found to be endoenergetic and the bicyclic product formed was found to have C 2 v symmetry, with the peroxide moiety in the syn configuration. Three possible reaction routes were studied: (i) concerted cycloaddition, (ii) stepwise cheletropic cycloaddition with the formation of zwitterionic 2,5-dihydrofuran l-oxide as an intermediate, and (iii) stepwise cycloaddition with the formation of a linear intermediate. In the case of butadiene routes (i) and (ii) were excluded, because only second-order saddle points were found on the corresponding reaction pathways. The linear intermediate (I1) found in route (iii) has a biradical character, and its energy relative to that of the separate reactants is 4.1 kcal/mol. The dominant activation barrier corresponds to the transition structure T1 leading to I1 and amounts to 9.9 kcal/mol. The rearrangement of I1 to the product (P) involves only a minor activation barrier of 7.5 kcal/mol (relative to I1). In the case of benzene the reaction occurs in a concerted manner with a single transition structure having C 2 v symmetry; the activation barrier is 25.3 kcal/mol. This difference in binding mechanism can be explained in terms of the configuration of the peroxide moiety in the adduct.

Theoretical Study of the Reaction of Vitamin B6 with 1O2

“…[15] The aim of this work was to study the reaction between pyridoxine and singlet oxygen. Pyridoxine has an aromatic six-membered ring, and as described by Bobrowski et al, [16] there are four principal types of oxygen-addition reactions to aromatic and unsaturated compounds: 1) 1,3-addition to a double bond connected to a hydrogen-carrying group, resulting in the formation of allylic hydroperoxides; Abstract: Singlet oxygen is known to cause oxidative stress in cells, leading to severe damage (e.g., lipid peroxidation, membrane degradation, mutagenic alterations to DNA, protein misfunctionality). Recently, pyridoxine has been discovered to be capable of quenching singlet oxygen, however, the mechanism of this reaction remains essentially unknown.…”

Ab initio study of the mechanism of singlet‐dioxygen addition to hydroxyaromatic compounds: Negative evidence for the involvement of peroxa and endoperoxide intermediates

“…In our recent study of dioxygen 1,4-addition to cis-1,3-butadiene and benzene 23 we found a peroxacyclopenta-3-ene species with relatively low energy. These species are unlikely to occur on the reaction path of the formation of 1,4-peroxides, because a simpler reaction mode with a lower activation barrier is available.…”

Determination of aromatic compounds by high‐performance liquid chromatography with on‐line photoreactor and peroxyoxalate chemiluminescence detection

“…Singlet oxygen is known to react with unsaturated compounds, including aromatic compounds, by several means (25). Addition of 1 O 2 to polycyclic aromatic compounds has been investigated in detail (26,27).…”

“…However, the addition of oxygen to benzene was generally thought to be unlikely reaction (27). Only the investigation of a mechanism of 1,4-oxygen addition to benzene in a one-step mechanism was reported by the study using CAS MCSCF/CAS MCQDPT2 (25). This mechanism was considered to be based on a reaction similar to that of ANT.…”