Theoretical studies of the isoprene ozonolysis under trropospheric conditions. 2. Unimolecular and water-assisted decomposition of the α-hydroxy hydroperoxides

9 paeges, 6 figures, 1 scheme, 3 tables.-- Printed version published Jul, 31, 2003.-- Supporting information available at: http://pubs.acs.org/doi/suppl/10.1021/jp034203wTheoretical studies of the unimolecular and water-assisted decomposition reactions of the α-hydroxy hydroperoxides compounds produced during the isoprene ozonolysis have been investigated in this paper. Geometrical parameters of all the stationary points as well as energies and rate constants have been computed by means of several ab initio and DFT methods (B3LYP, CCSD(T), and G2M-RCC5 levels). Our calculations indicate that only the water-assisted decomposition of the α-hydroxy hydroperoxides could be active in the atmosphere. The main reaction products are predicted to be H2O2 plus methyl vinyl ketone (MVK) or methacroleine (MAC), depending on the particular α-hydroxy hydroperoxide considered. In both cases the reaction is endothermic by about 19 kcal mol-1.The financial support for this work was provided by the Dirección General de Investigación Científica y Técnica (DGICYT, Grant BQU2002-0485-C02-01) and by the Generalitat de Catalunya (Grant 2001SGR00048).Peer reviewe

Influence of strong transannular N → P interaction on acidity of cyclenphosphine sulfide

International audienceThe acid-base behavior of cyclenphosphine sulfide (cyclenPS) is appreciably different from that of cyclamphosphine sulfide (cyclamPS). The cyclenPS shows five acid functionalities compared to four for cyclamPS. The fifth acidic group in cyclenPS corresponds to the formation of a stable amidure in aqueous solution (pK(a5) = 12.3). This behavior is due to the strong transannular N → P interaction. The deprotonation sequences were established by 31P-NMR and confirmed by modelling of cyclenPS

Magnetic measurements, UV-Vis spectroscopy, and XAS of dinuclear nickel(II) complexes of bistetraazamacrocycles

cited By 11International audienceThe nickel(II) complexes of N,N′-xylylenebis(tetraazamacrocycles) have been isolated. The description of these dinuclear bismacrocyclic complexes have been carried out by means of magnetic measurements and spectrophotometric experiments (UV-Vis). The metal environment and the ligand shape have been specified by XANES and EXAFS experiments, since attempts to obtain suitable crystals failed. © 2004 Elsevier Ltd. All rights reserved

XAS, ESR and potentiometric studies of three dinuclear N,N′-para-xylylenebis(tetraazamacrocycle)copper(II) complexes - X-ray crystal structure of [N,N′-p-xylylenebis(cyclen)]copper(II)

cited By 21International audienceDicopper complexes with N,N′-p-xylylenebis(cyclam or cyclen) and with the heteroditopic N,N′-p-xylylenebis(cyclam-cyclen) were synthesized. An X-ray study of the N,N′- p-xylylenebis(cyclen)dicopper complex showed that the copper(II) ion is five-coordinate with an H2O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS- anion are coordinated in apical position to the square-pyramidal copper(II) ion. Two alternating kinds of Cu2L4+ moieties are present in the chain, the first with two N4S chromophores and the second with two N5 chromophores. EXAFS and XANES results are in agreement with a five-coordinate copper ion in the cyclen unit and a six-coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu2L4+ species (ligand/metal ratio < 1) and mononuclear CuLHn(2+n)+ species (ligand/metal ratio > 1) were confirmed by an ESR study at variable pH. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003

XAS, ESR and potentiometric studies of three dinuclear N,N′-para-xylylenebis(tetraazamacrocycle)copper(II) complexes - X-ray crystal structure of [N,N′-p-xylylenebis(cyclen)]copper(II)

cited By 21International audienceDicopper complexes with N,N′-p-xylylenebis(cyclam or cyclen) and with the heteroditopic N,N′-p-xylylenebis(cyclam-cyclen) were synthesized. An X-ray study of the N,N′- p-xylylenebis(cyclen)dicopper complex showed that the copper(II) ion is five-coordinate with an H2O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS- anion are coordinated in apical position to the square-pyramidal copper(II) ion. Two alternating kinds of Cu2L4+ moieties are present in the chain, the first with two N4S chromophores and the second with two N5 chromophores. EXAFS and XANES results are in agreement with a five-coordinate copper ion in the cyclen unit and a six-coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu2L4+ species (ligand/metal ratio < 1) and mononuclear CuLHn(2+n)+ species (ligand/metal ratio > 1) were confirmed by an ESR study at variable pH. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003