Dynamic Solvent Effects in the Degenerate Isomerization of a Hexafluoroacetone Anil Studied by High-Pressure 19 F NMR

1999 ◽  
Vol 54 (6-7) ◽  
pp. 417-421
Author(s):  
Yasushi Ohga ◽  
Tsutomu Asano ◽  
Norbert Karger ◽  
Thomas Gross ◽  
Hans-Dietrich Lüdemann
Keyword(s):  
High Pressure ◽  
Nmr Spectroscopy ◽  
Transition State ◽  
Solvent Effects ◽  
Transition State Theory ◽  
State Theory ◽  
Nonequilibrium Conditions ◽  
19 F Nmr

Abstract The rate of the degenerate isomerization of N-hexafluoroisopropylidene-N’,N’-dimethyl-ρ-phe-nylenediamine was measured by high-pressure 19F NMR spectroscopy in a viscous hydrocar-bon, 2,4-dicyclohexyl-2-methylpentane. Pressure-induced retardations that cannot be rationalized within the framework of the transition state theory (TST) were observed, and it was concluded that the reaction was cast into the TST-invalid nonequilibrium conditions by high pressure.

On the Calculation of Transition State Activity Coefficient and Solvent Effects on Chemical Reactions

1998 ◽  
Vol 63 (12) ◽  
pp. 1969-1976 ◽  
Author(s):  
Alvaro Domínguez ◽  
Rafael Jimenez ◽  
Pilar López-Cornejo ◽  
Pilar Pérez ◽  
Francisco Sánchez
Keyword(s):  
Activity Coefficient ◽  
Transition State ◽  
Chemical Reactions ◽  
Solvent Effects ◽  
Transition State Theory ◽  
Reaction Medium ◽  
State Theory ◽  
Precursor Complex ◽  
State Activity ◽  
Classical Transition

Solvent effects, when the classical transition state theory (TST) holds, can be interpreted following the Brønsted equation. However, when calculating the activity coefficient of the transition state, γ# it is important to take into account that this coefficient is different from that of the precursor complex, γPC. The activity coefficient of the latter is, in fact, that calculated in classical treatments of salt and solvent effects. In this paper it is shown how the quotients γ#/γPC change when the reaction medium changes. Therefore, the conclusions taken on the basis of classical treatments may be erroneous.

scholarly journals Association of Cl with C2H2by unified variable-reaction-coordinate and reaction-path variational transition-state theory

2020 ◽  
Vol 117 (11) ◽  
pp. 5610-5616
Author(s):  
Linyao Zhang ◽  
Donald G. Truhlar ◽  
Shaozeng Sun
Keyword(s):  
High Pressure ◽  
Transition State ◽  
Transition State Theory ◽  
Reaction Path ◽  
State Theory ◽  
Reaction Coordinate ◽  
Acetylene Molecule ◽  
Variational Transition State Theory ◽  
Pressure Limit ◽  
Variational Transition State

Barrierless unimolecular association reactions are prominent in atmospheric and combustion mechanisms but are challenging for both experiment and kinetics theory. A key datum for understanding the pressure dependence of association and dissociation reactions is the high-pressure limit, but this is often available experimentally only by extrapolation. Here we calculate the high-pressure limit for the addition of a chlorine atom to acetylene molecule (Cl + C2H2→C2H2Cl). This reaction has outer and inner transition states in series; the outer transition state is barrierless, and it is necessary to use different theoretical frameworks to treat the two kinds of transition state. Here we study the reaction in the high-pressure limit using multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) at the outer transition state and reaction-path variational transition state theory (RP-VTST) at the inner turning point; then we combine the results with the canonical unified statistical (CUS) theory. The calculations are based on a density functional validated against the W3X-L method, which is based on coupled cluster theory with single, double, and triple excitations and a quasiperturbative treatment of connected quadruple excitations [CCSDT(Q)], and the computed rate constants are in good agreement with some of the experimental results. The chlorovinyl (C2H2Cl) adduct has two isomers that are equilibrium structures of a double-well C≡C–H bending potential. Two procedures are used to calculate the vibrational partition function of chlorovinyl; one treats the two isomers separately and the other solves the anharmonic energy levels of the double well. We use these results to calculate the standard-state free energy and equilibrium constant of the reaction.

Static Solvent Effects, Transition-State Theory

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Transition State ◽  
Rate Constant ◽  
Solvent Effects ◽  
Transition State Theory ◽  
Equilibrium Structure ◽  
State Theory ◽  
Potential Of Mean Force ◽  
Distribution Functions ◽  
Average Force ◽  
Activated Complex

This chapter discusses static solvent effects on the rate constant for chemical reactions in solution. It starts with a brief discussion of the thermodynamic formulation of transition-state theory. The static equilibrium structure of the solvent will modify the potential energy surface for the chemical reaction. This effect is analyzed within the framework of transition-state theory. The rate constant is expressed in terms of the potential of mean force at the activated complex. Various definitions of this potential and their relations to n-particle- and pair-distribution functions are considered. The potential of mean force may, for example, be defined such that the gradient of the potential gives the average force on an atom in the activated complex, Boltzmann averaged over all configurations of the solvent. It concludes with a discussion of a relation between the rate constants in the gas phase and in solution.

scholarly journals Kinetic effects of molecular clustering and solvation by extended networks in zeolite acid catalysis

2021 ◽  
Vol 12 (13) ◽  
pp. 4699-4708
Author(s):  
Jason S. Bates ◽  
Rajamani Gounder
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Heterogeneous Catalysts ◽  
Transition State Theory ◽  
Acid Catalysis ◽  
State Theory ◽  
Molecular Networks ◽  
Kinetic Effects ◽  
Molecular Clustering

“Solvent effects” at interfaces in heterogeneous catalysts are described by transition state theory treatments that identify kinetic regimes associated with molecular clustering and the solvation of such clusters by extended molecular networks.

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