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Different Reaction Pathways (different + reaction_pathway)
Selected AbstractsCatalytic cleavage of methyl oleate or oleic acidEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 1 2010Angela Köckritz Abstract Different reaction pathways are discussed for the Os-catalyzed oxidation of methyl oleate and oleic acid using O2/aldehyde as oxidation system. Monomethyl azelate and pelargonic acid were the main products obtained in yields of approximately 50,70% starting from methyl oleate. Besides, varying amounts of methyl 9,10-epoxystearate and methyl 9,10-dihydroxystearate were found as by-products. Azelaic acid and pelargonic acid were obtained exclusively from oleic acid used as reactant. Some mechanistic considerations led to the conclusion that the observed products are formed in parallel reaction paths. The effective oxidant for the scission of the C=C double bond seems to be very likely an in situ formed peracid generated by Os-catalysis from O2/aldehyde. Additional investigations concerning the cleavage of oleic acid and methyl oleate with in situ formed performic acid from H2O2/formic acid corroborate this assumption. [source] Transition States of the Asymmetric Michael Reactions of Aldehydes Catalyzed by Trimethylsilyl-Protected DiphenylprolinolEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2009Jian-Qiang Zhao Abstract The asymmetric Michael reactions of aldehydes and nitroalkenes catalyzed by trimethylsilyl-protected diphenylprolinol were investigated by using density functional theory calculations. As a result of the stereospecific blockade of the bulky diphenylsiloxymethyl group on the pyrrolidine ring, the Re face of the enamine double bond is effectively shielded. For acetaldehyde, there are two different conformers of the enamine intermediate. On the basis of the two conformers of the enamine intermediate, four different reaction pathways were considered and four different transition states were searched for the enantioselective asymmetric Michael reaction of acetaldehyde and nitroalkene. The lowest- and second-lowest-energy transition states are both formed via the same intermediate IM2. The enantiomeric excess, calculated to be 96,%,ee, is in good agreement with the experimental value. For propanal, on the basis of the four different conformers of the prolinol,enamine intermediate, eight different reaction pathways were considered and eight transition states were searched for the enantioselective asymmetric Michael reaction. The calculated ee value is 99.5,%, which is in good agreement with the experimental ee value of 99,%. The lowest- and second-lowest-energy transition states are formed via different enamine intermediates, which is different from the case of acetaldehyde. The calculations also reveal that the intermediates play an important role in the reactions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Structure-sensitivity of CH3 dissociation on Ni(100)from first-principles calculationsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Yi-An Zhu Abstract First-principles calculations are performed to explore the CH3 dissociation on Ni(100). The CH2 species bind most strongly to the hollow site with two CH bonds pointing toward the neighboring surface Ni atoms. Through the calculations of local density of states (LDOSs) and partial charge density, the CHNi three-center bond is regarded as the key factor determining the CH3 adsorption. The CH3 dissociation on Ni(100) is investigated along two different reaction pathways. After zero-point energy (ZPE) correction considered, the energy barriers for the CH3 dehydrogenation are calculated to be 0.46 and 0.54 eV. Because these barriers are much lower than that for the CH3 dissociation on Ni(111), the CH3 dehydrogenation is found to be structure-sensitive. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Transmetalation Reactions from Fischer Carbene Complexes to Late Transition Metals: A DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008Israel Fernández Dr. Abstract Transmetalation reactions from chromium(0) Fischer carbene complexes to late-transition-metal complexes (palladium(0), copper(I), and rhodium(I)) have been studied computationally by density functional theory. The computational data were compared with the available experimental data. In this study, the different reaction pathways involving the different metal atoms have been compared with each other in terms of their activation barriers and reaction energies. Although the reaction profiles for the transmetalation reactions to palladium and copper are quite similar, the computed energy values indicate that the process involving palladium as catalyst is more favorable than that involving copper. In contrast to these transformations, which occur via triangular heterobimetallic species, the transmetalation reaction to rhodium leads to a new heterobimetallic species in which a carbonyl ligand is also transferred from the Fischer carbene to the rhodium catalyst. Moreover, the structure and bonding situation of the so far elusive heterobimetallic complexes are briefly discussed. La reacción de transmetalación catalítica desde cromo(0) Fischer carbenos a metales de transición tardía (Pd0, CuIand RhI) se ha estudiado computacionalmente usando DFT. Los resultados computacionales se han comparado con los datos experimentales disponibles. Las barreras y las energías de reacción se han comparado en los caminos de reacción obtenidos para los metales considerados. Mientras que los perfiles de reacción para la transmetalación desde Cr a Pd o Cu son similares, los valores calculados indican que aquellos procesos que implican catalizadores de Pd son más favorables que los que implican Cu. En claro contraste con estas transformaciones, que ocurren a través de especies heterobimetálicas con geometría triangular, la reacción con Rh forma nuevas especies heterobimetálicas en las que se ha transferido un ligando carbonilo desde el complejo de Fischer al catalizador de Rh. Adicionalmente, se discute la estructura y la forma de enlace de éstos complejos heterobimetálicos no aislados hasta este momento. [source] The Reaction of o -Alkynylarene and Heteroarene Carboxaldehyde Derivatives with Iodonium Ions and Nucleophiles: A Versatile and Regioselective Synthesis of 1H -Isochromene, Naphthalene, Indole, Benzofuran, and Benzothiophene CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2006José Barluenga Prof. Dr. Abstract The reaction of o -alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy2BF4, at room temperature, gave functionalized 4-iodo-1H -isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o -alkynylbenzaldehyde derivatives with IPy2BF4 stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o -hexynylbenzaldehyde 1,b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism. [source] | ||||||||||