Topic
Transition state
About: Transition state is a research topic. Over the lifetime, 4978 publications have been published within this topic receiving 117965 citations. The topic is also known as: transition state of elementary reaction.
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TL;DR: In this paper, the solvent effects for a Claisen rearrangement and a Diels-Alder reaction were investigated in terms of the locations and magnitudes of the curvature peaks along the reaction path, as well as the shape of the potential energy near the reaction coordinate near the transition state.
Abstract: The solvent effects for a Claisen rearrangement and a Diels-Alder reaction are investigated. Electronic structure methods are used to generate the frequencies, couplings, and curvatures along the minimum energy paths for these reactions in the gas phase and in the presence of two water molecules. The geometries and charge distributions along the minimum energy paths are analyzed to determine the structural and electrostatic roles of the water molecules. Reactive flux molecular dynamics methods based on a reaction path Hamiltonian are used to calculate the dynamical transmission coefficients, which account for recrossings of the transition state. The transmission coefficients for the Claisen rearrangement are nearly unity both in the gas phase and in the presence of two water molecules. The transmission coefficients for the Diels-Alder reaction are 0.95 and 0.89 in the gas phase and in the presence of two water molecules, respectively. These differences in the transmission coefficients are explained in terms of the locations and magnitudes of the curvature peaks along the reaction path, as well as the shape of the potential energy along the reaction coordinate near the transition state. Analysis of the dynamical trajectories provides insight into the dynamical role of the water molecules and elucidates possible reaction mechanisms.
37 citations
TL;DR: It appears that the transition states for phosphoryl transfer have no more than one negative charge on the nonbridge oxygens, so that reactions of monoesters are dissociative, reactions of triesters are associative, and reactions of diesters are SN2 with half bond order to entering and leaving groups.
Abstract: Secondary 18O isotope effects have been developed as a tool for determining transition state structures in enzymatic and nonenzymatic phosphoryl transfer reactions. 18O substitution in the nonbridge oxygens of a phosphoryl group makes the reaction go faster when the bond order is higher to these oxygens in the transition state than in the reactant, whereas the reaction goes slower if the bond order is less. The isotope effects are measured by the remote label method, using an isotope ratio mass spectrometer for analysis. The bond order to p-nitrophenolate ion when it is the leaving group is indicated by the secondary 15N isotope effect in the nitro group, with a value of 1.0028 representing nearly complete bond cleavage. It appears that the transition states for phosphoryl transfer have no more than one negative charge on the nonbridge oxygens, so that reactions of monoesters are dissociative, reactions of triesters are associative, and reactions of diesters are SN2 with half bond order to entering and le...
37 citations
TL;DR: A review of the double many-body expansion of molecular potential energy functions and the role of long-range forces in the rates of chemical reactions is given in this paper, where the O+OH→O2+H and H+H2→H 2+H reactions are discussed.
Abstract: A review is given of the double many-body expansion (DMBE) of molecular potential energy functions and of the role of long-range forces - these being properly described in the DMBE - in the rates of chemical reactions. The O+OH→O2+H and H+H2→H2+H reactions are discussed. New thermal rate coefficients for the former reaction are also reported from the assumption of loose transition states.
37 citations
TL;DR: A full computational description of the fragmentation reactions of protonated diglycine (H+GG) is presented, and the mechanism for the combined loss of carbon monoxide and ammonia is explored for the first time.
37 citations
TL;DR: In this paper, the structure, energies, and vibrational frequencies of various intermediates and transition states in the reaction between phosphines and singlet oxygen have been calculated using ab initio methods, including RHF, MP2, and CASSCF optimizations, and energy evaluations using various basis sets including electron correlation.
Abstract: Structures, energies, and vibrational frequencies of various intermediates and transition states in the reaction between phosphines and singlet oxygen have been calculated using ab initio methods, including RHF, MP2, and CASSCF optimizations, and energy evaluations using various basis sets including electron correlation. A surprising result is that the only intermediate located for the first step of the reaction has the cyclic phosphadioxirane structure. An acyclic intermediate is not stable. This result contrasts strongly with the reaction of sulfides, where both cyclic and open structures are stable. Improved calculations for thiadioxirane and peroxy sulfoxide are reported
37 citations