3 research outputs found
Mechanism of the hydrogen transfer from the OH group to oxygen-centered radicals: proton-coupled electron-transfer versus radical hydrogen abstraction
No full text7 pages, 4 figures, 4 schemes, 2 tables.-- PMID: 15371559 [PubMed].-- Printed version Jul 19, 2004.[EN] High-level ab initio electronic structure calculations have been carried out with respect to the intermolecular hydrogen-transfer reaction HCOOH+.OHHCOO.+H2O and the intramolecular hydrogen-transfer reaction .OOCH2OHHOOCH2O.. In both cases we found that the hydrogen atom transfer can take place via two different transition structures. The lowest energy transition structure involves a proton transfer coupled to an electron transfer from the ROH species to the radical, whereas the higher energy transition structure corresponds to the conventional radical hydrogen atom abstraction. An analysis of the atomic spin population, computed within the framework of the topological theory of atoms in molecules, suggests that the triplet repulsion between the unpaired electrons located on the oxygen atoms that undergo hydrogen exchange must be much higher in the transition structure for the radical hydrogen abstraction than that for the proton-coupled electron-transfer mechanism. It is suggested that, in the gas phase, hydrogen atom transfer from the OH group to oxygen-centered radicals occurs by the proton-coupled electron-transfer mechanism when this pathway is accessible.[CT] S'han realitzat c脿lculs d'estructura electr貌nica ab initio d'alt nivell per la reacci贸 de transfer猫ncia d'hidrogen intermolecular HCOOH+.OHHCOO.+H2O i per la reacci贸 de transfer猫ncia d'hidrogen intramolecular .OOCH2OHHOOCH2O.. En abmd贸s casos trobem que la transfer猫ncia de l'脿tom d'hidrogen t茅 lloc via dues estructures de transici贸 diferents. L'estructura de transici贸 d'energia m茅s bixa implica una transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸 des de l'esp猫cie ROH al radical, mentre que l'estructura de transici贸 d'energia m茅s alta correspon a una abstracci贸 d'hidrogen radical脿ria convencional. Una an脿lisi de les poblacions 脿tomiques d'sp铆n electr貌nic, calculades en el marc de la teoria topol貌gica d'脿toms en mol猫cules, suggereix que la repulsi贸 dels electrons no aparellats localitzats sobre els 脿toms d'oxigen que experimenten el bescanvi d'hidrogen ha de ser molt m茅s alta en l'estructura de transici贸 per l'abstracci贸 d'hidrogen radical脿ria que en l'estructura de transici贸 del mecanisme de transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸. Es suggereix que, en fase gas, les transfer猫ncies de l'脿tom d'hidrogen de l'OH a radicals d'oxigen tenen lloc per un mecanisme de transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸 quan aquest cami de reacci贸 茅s accessible.This research was supported by the Spanish DGICYT (Grants BQU2002-04485-C02-01, BQU2002-04485-C02-02, and BQU2002-00293). Additional support came from Catalonian CIRIT (Grant 2001SGR00048).Peer reviewe
Mechanism of the hydrogen transfer from the OH group to oxygen-centered radicals: proton-coupled electron-transfer versus radical hydrogen abstraction
No full text7 pages, 4 figures, 4 schemes, 2 tables.-- PMID: 15371559 [PubMed].-- Printed version Jul 19, 2004.[EN] High-level ab initio electronic structure calculations have been carried out with respect to the intermolecular hydrogen-transfer reaction HCOOH+.OHHCOO.+H2O and the intramolecular hydrogen-transfer reaction .OOCH2OHHOOCH2O.. In both cases we found that the hydrogen atom transfer can take place via two different transition structures. The lowest energy transition structure involves a proton transfer coupled to an electron transfer from the ROH species to the radical, whereas the higher energy transition structure corresponds to the conventional radical hydrogen atom abstraction. An analysis of the atomic spin population, computed within the framework of the topological theory of atoms in molecules, suggests that the triplet repulsion between the unpaired electrons located on the oxygen atoms that undergo hydrogen exchange must be much higher in the transition structure for the radical hydrogen abstraction than that for the proton-coupled electron-transfer mechanism. It is suggested that, in the gas phase, hydrogen atom transfer from the OH group to oxygen-centered radicals occurs by the proton-coupled electron-transfer mechanism when this pathway is accessible.[CT] S'han realitzat c脿lculs d'estructura electr貌nica ab initio d'alt nivell per la reacci贸 de transfer猫ncia d'hidrogen intermolecular HCOOH+.OHHCOO.+H2O i per la reacci贸 de transfer猫ncia d'hidrogen intramolecular .OOCH2OHHOOCH2O.. En abmd贸s casos trobem que la transfer猫ncia de l'脿tom d'hidrogen t茅 lloc via dues estructures de transici贸 diferents. L'estructura de transici贸 d'energia m茅s bixa implica una transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸 des de l'esp猫cie ROH al radical, mentre que l'estructura de transici贸 d'energia m茅s alta correspon a una abstracci贸 d'hidrogen radical脿ria convencional. Una an脿lisi de les poblacions 脿tomiques d'sp铆n electr貌nic, calculades en el marc de la teoria topol貌gica d'脿toms en mol猫cules, suggereix que la repulsi贸 dels electrons no aparellats localitzats sobre els 脿toms d'oxigen que experimenten el bescanvi d'hidrogen ha de ser molt m茅s alta en l'estructura de transici贸 per l'abstracci贸 d'hidrogen radical脿ria que en l'estructura de transici贸 del mecanisme de transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸. Es suggereix que, en fase gas, les transfer猫ncies de l'脿tom d'hidrogen de l'OH a radicals d'oxigen tenen lloc per un mecanisme de transfer猫ncia de prot贸 acoblada a la transfer猫ncia d'un electr贸 quan aquest cami de reacci贸 茅s accessible.This research was supported by the Spanish DGICYT (Grants BQU2002-04485-C02-01, BQU2002-04485-C02-02, and BQU2002-00293). Additional support came from Catalonian CIRIT (Grant 2001SGR00048).Peer reviewe
