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.

Theoretical study of the pyrolysis of methyltrichlorosilane in the gas phase. 2. Reaction paths and transition states.

Abstract: The kinetics for the previously proposed 114-reaction mechanism for the chemical vapor deposition (CVD) process that leads from methyltrichlorosilane (MTS) to silicon carbide (SiC) are examined. Among the 114 reactions, 41 are predicted to proceed with no intervening barrier. For the remaining 73 reactions, transition states and their corresponding barrier heights have been explored using second-order perturbation theory (MP2) with the aug-cc-pVDZ basis set. Final energies for the reaction barriers were obtained using both MP2 with the aug-cc-pVTZ basis set and coupled cluster theory (CCSD(T)) with the aug-cc-pVDZ basis set. CCSD(T)/aug-cc-pVTZ energies were estimated by assuming additivity of basis set and correlation effects. Partition functions for the computation of thermodynamic properties of the transition states were calculated with MP2/aug-cc-pVDZ. Forward and reverse Gibbs free energy barriers were obtained at 11 temperatures ranging from 0 to 2000 K. Important reaction pathways are illustrated at 0 and 1400 K.

Substitution at saturated carbon. Part XIV. Solvent effects on the free energies of ions, ion-pairs, non-electrolytes, and transition states in some SN and SE reactions

Abstract: Standard free energies of transfer from methanol to various other solvents are reported for dissociated species R4N++ X–(20–30 solvents), ion pairs R4NX (20–30 solvents), t-butyl chloride (20 solvents), t-butyl bromide (10 solvents), tetramethyltin (15 solvents), tetraethyltin (15 solvents), and tetraethyl-lead (10 solvents). A dissection on solvent influences on ΔG‡ into initial-state and transition-state contributions has been accomplished for the decomposition of t-butyl chloride (18 solvents), the decomposition of t-butyl bromide (10 solvents), the Menschutkin reaction of NN-dimethylaniline with methyl iodide (3 solvents), and the iododemetallation of tetra-alkyl-leads (8 solvents).A comparison of solvent effects on the free energies of ion pairs with solvent effects on the free energies of transition states suggests that transition states carry the following units of charge separation: [ButCl]‡ 0·70 (polar solvents), [graphic omitted] 0·5 (non-polar solvents); [ButBr]‡ 0·68 (polar solvents); [p-NO2·C6H4·CH2Cl–Me3N]‡ 0·35. Charge separation in the [R4Pb–l2]‡ transition states is probably rather higher than in the transition state of the Menschutkin reaction.

The Quest for Ring Opening of Oxaphosphirane Complexes: A Coupled‐Cluster and Density Functional Study of CH3PO Isomers and Their Cr(CO)5 Complexes

Abstract: Opening gambit: A high-level theoretical study on the relative stabilities of oxaphosphirane isomers and their Cr(CO)(5) complexes is reported (see picture). Furthermore, thermodynamics and kinetics of possible ring-opening reactions of these complexes in the presence of a {Cp(2)Ti(III)Cl} fragment are theoretically investigated. The C--O bond cleavage is predicted to be the most efficient pathway, thus leading to reactive intermediates that are attractive for synthetic applications.A high-level theoretical study on the relative stabilities of oxaphosphirane isomers and their Cr(CO)(5) complexes is reported. Furthermore, thermodynamics and kinetics of possible ring-opening reactions of these complexes in the presence of a {Cp(2)Ti(III)Cl} fragment are theoretically investigated. The C--O bond cleavage is predicted to be the most efficient pathway thus leading to reactive intermediates that are attractive for synthetic applications. The ring-opening reaction is predicted to not lead to the most favorable product (a coordinated phosphinidene oxide species). Rather, the ring-opening product is separated by a substantial barrier of about 24 kcal mol(-1) from the thermodynamically most favorable species.

Density functional theory calculations of the energetics and kinetics of jet fuel autoxidation reactions

Abstract: Density functional theory calculations of the energetics and kinetics of important reactions for jet fuel oxidation are reported. The B3LYP functional along with 6-31G(d) and larger basis sets are used for calculation of peroxy radical abstraction reactions from hydrocarbons and heteroatomic species, the reaction of sulfides, disulfides, and phosphines with hydroperoxides to produce nonradical products, and the metal catalysis of hydroperoxide decomposition. Reaction enthalpies and activation energies are determined via DFT calculations of the structures and energies of stable species and transition states. The peroxy radical abstraction study shows the high reactivity (Ea's of 6−11 kcal/mol) of the H atoms which are weakly bonded to heteroatoms, including nitrogen, oxygen, and sulfur. These species, at part-per-million levels, are able to compete for peroxy radicals with the bulk fuel hydrocarbon species. Benzylic hydrogens on aromatic hydrocarbons are shown to be significantly more reactive (by 4 to 5 k...