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.

Strain-Dependent Acceleration of a Paradigmatic SN2 Reaction Accurately Predicted by the Force Formalism

Abstract: Experiment and theory suggest that the effect of strain on the kinetics of SN2 reactions is predicted accurately within the force formalism using a single structural parameter, the difference of the nonbonding separation of two atoms bound to the electrophilic atom in the ground and transition states of the corresponding strain-free reaction. We show that the difference of the H3C···OMs distance in EtOMs (Ms: SO2Me) and that in the corresponding transition state of its hydrolysis, H2O···(Me)CH2···OMs, calculated at the B3LYP/6-311++G(3df,2pd) level with the SMD solvent model accurately predicts the measured lowering of the free energy of activation across a series of increasingly strained macrocyclic sulfonates. The equivalent distance H2C···S in EtSSEt also accurately predicts the previously reported kinetics of thiol/disulfide exchange in strained disulfides. The elongation of the scissile C−O or S−S bond yields qualitatively incorrect predictions. The results are consistent with the established structu...

Ab initio molecular orbital study on the oxidation mechanism for dimethylamine borane as a reductant for an electroless deposition process

Abstract: The oxidation mechanism of dimethylamine borane (DMAB) as a reductant for an electroless deposition process was studied by an ab initio molecular orbital method. Two types of reaction pathways, via either three-coordinate borane molecules obtained by primary dehydrogenation reactions, or five-coordinate ones by primary additions of OH- for the oxidation of the DMAB, were examined. While the former pathway corresponds to the general oxidation mechanism of the reductant proposed by Meerakker, the present theoretical results support the latter one. Furthermore, it was clarified that an electron emission occurs when OH- adds to the four-coordinate compounds, which agrees with the Meerakker's mechanism. Results of the normal-mode analyses showed that the five-coordinate compounds are the transition states. The optimized geometries of monoanion five-coordinate molecules are nearly bipyramidal. The charge and spin-population analyses indicated that the axial bondings in the five-coordinate compounds are stabiliz...

Ab Initio MO Study of the Triplet C3H4 Potential Energy Surface and the Reaction of C(3Pj) with Ethylene, C2H4

Abstract: The potential energy surface for the reaction of C(3Pj) with ethylene, C2H4(X1Ag), has been investigated using the G2M method. Structures of the stationary points and transition states for various isomerization and dissociation pathways of triplet C3H4 have been studied. The results show that at the initial step of the C(3Pj) + C2H4(X1Ag) reaction carbon atom attacks the π-orbital of the C2H4 molecule yielding cyclopropylidene i1 without entrance barrier. i1 then isomerizes to the triplet allene i3 via ring opening. The latter either splits a hydrogen atom producing the propargyl radical p3 + H or undergoes a 1,2-H shift to vinylmethylene, which in turn gives H2CCCH (p3) + H. The propargyl radical is concluded to be a nearly exclusive product of the C(3P) + C2H4 reaction. At the internal energy of 9.2 kcal/mol above the reactants level, Rice−Ramsperger−Kassel−Marcus calculations show about 93% of H2CCCH comes from fragmentation of triplet allene and 7% from vinylmethylene. The formation of CH2(3B1) + C2H2...

Quantum Chemical and RRKM Investigation of the Elementary Channels of the Reaction C6H6 + O (3P)

Abstract: We performed a computational study of an important reaction in the combustion of hydrocarbons, C6H6, + O (3P), using ab initio and RRKM methods. Density functional theory (B3LYP) was used to optimize geometries and obtain molecular vibrational frequencies, and complete basis set extrapolation (CBS-QB3) was used to obtain the energies for the reactants several transition states and products. The initial formation of a stabilized adduct is characterized by a barrier of 4.9 kcal mol-1, in good agreement with the measured activation energy for this reaction. All product channels originate from rearrangement or decomposition of this adduct, which our calculations suggest is a triplet ground state. All of our ab initio calculations are thus conducted on the triplet surface. There are several products that are energetically accessible at combustion temperatures, but the formation of phenoxy radical, C6H5O, and H atom dominate the product slate at low temperatures. Rearrangement to form formylcyclopentadiene, C5H...