[Importance of incorporation body mass index in organization of physical training in universities]

The studies indicate that students underweight stress regulatory mechanisms were significantly higher during the first academic year, compared to female students with normal body weight and thus "price physiological adaptation" higher. Requiring individual implementation of programs in the classroom for physical education at the educational process

A quantum-chemical study of the oxidation of ethylene by peroxyacetic acid derivatives

Density functional theory (B3LYP/6-31G(d, p)) and the Möller-Plesset perturbation theory (MP2/6-31G(d, p)) were used to study the electronic and geometric structure and relative stability of possible peroxyacetic acid and its trifluorinated derivative tautomers (including conformers), R-C(=O)(-OOH), R = CH3, CF3. Four types of stable tautomers of both compounds were found, and the energy characteristics of transitions between them were determined. The results of quantum-chemical modeling were used to study some special features of the oxidation of ethylene with the participation of all the tautomeric forms of both peroxy acids. For the acyclic form (ground state) of both peroxy acids and its conformers, two reactions are possible, namely, epoxidation with the formation of ethylene oxide (plus acid) and hydroxylation with the formation of ethanediol acetate ester and/or its isomer acetaldehyde semiacetal. At the same time, the oxidation of ethylene with the participation of all the other tautomeric forms (dioxirane and tautomers of the type of carbonyl and water oxides) only results in ethylene epoxidation. © Pleiades Publishing, Ltd., 2010

Special features of ethylene epoxidation by peroxyacetic acid

The B3LYP/6-31G(d, p) method of density functional theory was used to study the influence of carboxylic acid and water molecules on parallel ethylene oxidation reactions (epoxidation and hydroxylation) by peroxyacetic acid with the formation of various products. It was shown that carboxylic acid in the nondissociated form always present in the reaction mixture for several reasons had a catalytic action on this reaction and therefore contributed to an increase in its selectivity. We also found that the water molecule and its dimer facilitated epoxide formation. The suggestion was made that, if the reaction was performed in an aqueous medium, where the acid dissociated, the situation could radically change, and the hydroxylation reaction with the formation of glycol and/or its ester of the corresponding carboxylic acid would become predominant. © 2010 Pleiades Publishing, Ltd

Special features of ethylene epoxidation by peroxyacetic acid

The B3LYP/6-31G(d, p) method of density functional theory was used to study the influence of carboxylic acid and water molecules on parallel ethylene oxidation reactions (epoxidation and hydroxylation) by peroxyacetic acid with the formation of various products. It was shown that carboxylic acid in the nondissociated form always present in the reaction mixture for several reasons had a catalytic action on this reaction and therefore contributed to an increase in its selectivity. We also found that the water molecule and its dimer facilitated epoxide formation. The suggestion was made that, if the reaction was performed in an aqueous medium, where the acid dissociated, the situation could radically change, and the hydroxylation reaction with the formation of glycol and/or its ester of the corresponding carboxylic acid would become predominant. © 2010 Pleiades Publishing, Ltd

A quantum-chemical study of the oxidation of ethylene by peroxyacetic acid derivatives

Density functional theory (B3LYP/6-31G(d, p)) and the Möller-Plesset perturbation theory (MP2/6-31G(d, p)) were used to study the electronic and geometric structure and relative stability of possible peroxyacetic acid and its trifluorinated derivative tautomers (including conformers), R-C(=O)(-OOH), R = CH3, CF3. Four types of stable tautomers of both compounds were found, and the energy characteristics of transitions between them were determined. The results of quantum-chemical modeling were used to study some special features of the oxidation of ethylene with the participation of all the tautomeric forms of both peroxy acids. For the acyclic form (ground state) of both peroxy acids and its conformers, two reactions are possible, namely, epoxidation with the formation of ethylene oxide (plus acid) and hydroxylation with the formation of ethanediol acetate ester and/or its isomer acetaldehyde semiacetal. At the same time, the oxidation of ethylene with the participation of all the other tautomeric forms (dioxirane and tautomers of the type of carbonyl and water oxides) only results in ethylene epoxidation. © Pleiades Publishing, Ltd., 2010

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

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

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