Tautomerism of peroxyacetic acid derivatives: A quantum chemical study

The electronic and molecular structures and the relative stabilities of organic peracids X=C(R)-COOH and their cyclic tautomers, dioxiranes HX-C(R)-C-O-O, with R = Me, CF3; X = O, NH, were studied using the ab initio Hartree-Fock method and the density functional theory (B3LYP version) as well as at the MP2-MP4 Møller- Plesset levels of perturbation theory. Geometry optimization was performed by the UHF and B3LYP methods with the 6-31G** basis set and at the MP2/cc-pvtz level of theory. The acyclic form of the peracid is more stable than the cyclic dioxirane form irrespective of the nature of the substituent. The energy difference between these tautomers increases as the CF3 and NH groups are replaced by Me and O, respectively. Parameters of the activation barrier to tautomeric conversion increase in parallel with enhancement of the electron-accepting properties of both substituents. The transition state of tautomeric interconversion, which is topologically similar to the acyclic structure of the carbonyl oxide derivative R(HX)C=O+-O-, was found and characterized taking peroxyacetic acid as an example. The characteristic features of the transition state are an intramolecular "multicenter" H-bond and the charge distribution that is inconsistent with the canonical structure mentioned above. An appropriate reaction coordinate for the transformation of the quasi-tetrahedral dioxirane structure into a planar peroxyacetic acid structure is provided by the dihedral angle. Deprotonated anionic systems are characterized by much smaller differences between the relative stabilities of the open and closed forms of isomers and by much lower activation barriers to isomeric conversions. © 2005 Springer Science+Business Media, Inc

Tautomerism of peroxyacetic acid derivatives: A quantum chemical study

The electronic and molecular structures and the relative stabilities of organic peracids X=C(R)-COOH and their cyclic tautomers, dioxiranes HX-C(R)-C-O-O, with R = Me, CF3; X = O, NH, were studied using the ab initio Hartree-Fock method and the density functional theory (B3LYP version) as well as at the MP2-MP4 Møller- Plesset levels of perturbation theory. Geometry optimization was performed by the UHF and B3LYP methods with the 6-31G** basis set and at the MP2/cc-pvtz level of theory. The acyclic form of the peracid is more stable than the cyclic dioxirane form irrespective of the nature of the substituent. The energy difference between these tautomers increases as the CF3 and NH groups are replaced by Me and O, respectively. Parameters of the activation barrier to tautomeric conversion increase in parallel with enhancement of the electron-accepting properties of both substituents. The transition state of tautomeric interconversion, which is topologically similar to the acyclic structure of the carbonyl oxide derivative R(HX)C=O+-O-, was found and characterized taking peroxyacetic acid as an example. The characteristic features of the transition state are an intramolecular "multicenter" H-bond and the charge distribution that is inconsistent with the canonical structure mentioned above. An appropriate reaction coordinate for the transformation of the quasi-tetrahedral dioxirane structure into a planar peroxyacetic acid structure is provided by the dihedral angle. Deprotonated anionic systems are characterized by much smaller differences between the relative stabilities of the open and closed forms of isomers and by much lower activation barriers to isomeric conversions. © 2005 Springer Science+Business Media, Inc

The role of multicenter hydrogen bonds in peracetic acid isomerization to the corresponding dioxirane

[No abstract available

Species with multicenter H-bonding in isomerization of peracetic acid into corresponding dioxirane

The ab initio quantum chemical methods are applied to investigate mutual transformations of peracetic acid and 3-methyl-1,2-dioxirane-3-ol. It is for the first time found that the peroxycarboxylic group proton is bonded simultaneously to three oxygen atoms as in both tautomers as well in the activated complex. Furthermore, it is found that the suitable tautomeric transition 'coordinate' has a complex character and can't be reduced to simple proton mode. Both peculiarities are substantial for tautomeric transition mechanism and make doubtful the adopted mechanism of olefin epoxidation since for both reactions the proton transfer stage is common

The role of multicenter hydrogen bonds in peracetic acid isomerization to the corresponding dioxirane

[No abstract available

Species with multicenter H-bonding in isomerization of peracetic acid into corresponding dioxirane

The ab initio quantum chemical methods are applied to investigate mutual transformations of peracetic acid and 3-methyl-1,2-dioxirane-3-ol. It is for the first time found that the peroxycarboxylic group proton is bonded simultaneously to three oxygen atoms as in both tautomers as well in the activated complex. Furthermore, it is found that the suitable tautomeric transition 'coordinate' has a complex character and can't be reduced to simple proton mode. Both peculiarities are substantial for tautomeric transition mechanism and make doubtful the adopted mechanism of olefin epoxidation since for both reactions the proton transfer stage is common