Eyring’s transition state theory

As such, it could be treated with the Eyring s transition state theory. When stated in general terms, the transition state theory is applicable to any physico-chemical process which is activated by thermal energy [94] ... 

The vertical axis is free energy, showing AGO for the net conversion of A to P, and AG, the activation free energy for each of the kinetic steps. According to Eyring s transition state theory (Chapter 7), AG is given by... 

The Marcus classical free energy of activation is AG , the adiabatic preexponential factor A may be taken from Eyring s Transition State Theory as (kg T /h), and Kel is a dimensionless transmission coefficient (0 < k l < 1) which includes the entire efiFect of electronic interactions between the donor and acceptor, and which becomes crucial at long range. With Kel set to unity the rate expression has only nuclear factors and in particular the inner sphere and outer sphere reorganization energies mentioned in the introduction are dominant parameters controlling AG and hence the rate. It is assumed here that the rate constant may be taken as a unimolecular rate constant, and if needed the associated bimolecular rate constant may be constructed by incorporation of diffusional processes as ... 

Based on the known vibrational modes, as well as the energy and geometry characteristics of the studied reactions, the rate constants can be estimated according to Eyring s Transition State Theory (TST). The canonical rate constant for a bimolecular reaction at a given temperature proceeds according to the following equation ... 

Returning to intermolecular electron transfer (outer-sphere electron transfer), we assume that the electronic coupling term V12 in the encounter pair (A -D) is sufficient to ensure a high probability of electron transfer at the crossing points, but much smaller than AG (0) = 2/4. The rate of electron transfer is then given by Eyring s transition state theory (Equation 5.6). 

In this way, the main computational challenge in the determination of the enzyme catalytic power is reduced to the calculation of the rate constant, which can be expressed, according to Eyring s transition state theory (TST) as... 

Three basic assumptions are involved in Eyring s transition state theory I. Statistical equilibrium between reactants and activated complexes. II. Classical motion along the reaction path. ... 

Temperature dependence of the fluorescence quantum yields and fluorescence lifetimes of frans-4,4 -di-fert-butylstilbene in n-hexane and n-tetradecane allowed to define the index of refraction dependence of the radiative rate constants, kf= (3.9 — 1.8) X 10 s, and fluorescence lifetime [78]. This relationship was used to calculate torsional relaxation rate constants ktp> for traws-4,4 -dimethyl- and frans-4,4 -di-ferf-butylstilbene in the n-alkane solvent series. It was found that activation parameters for ktp, based on Eyring s transition state theory, adhered to the medium-enhanced thermodynamic barrier model relationship, AHtp = AHt + aEr, and to the isokinetic relationship. The isokinetic relationship between the activation parameters for the parent frans-stilbene led to an isokinetic temperature of P = 600K and brings it into agreement with the isokinetic temperature for activation parameters based on estimated microviscosities, qp, experienced by stilbene in its torsional motion. The authors concluded that only microviscosities raflier than shear viscosities, q, can be employed in the expression ktp = ktSq — b, when a = b. These data clearly indicated the important role of the media dynamics in the stilbene cis-trans photoisomerization. 

From a chemical viewpoint, bond scission under stress is a particular case of a un-imolecular dissociation reaction whose rate is enhanced by mechanical stress. As such, it could be treated with Eyring s transition-state theory [Eq. (37)], which permits one to bring the treatment of rate processes within the scope of thermodynamic arguments. By combining de Boer s thermodynamic formulation and the transition-state theory, Tobolsky and Eyring in 1943 developed the rate theory for thermally activated fracture of polymeric threads. When put into an Arrhenius-... 

Eyring s transition-state theory was developed in the 1930s and strained every computational capability at that time. Now it is possible to use modem computer programs to study the rearrangement of the reactants along a reaction coordinate, which is different from the extent of reaction ... 

In 1954 Marcus, Zwolinski and Eyring developed a theory of electron transfer based on the hypothesis that the mechanism involves electron tunneling (sections 1.14 and 1.15). They assumed that solvents and ligands form a barrier through which electrons must pass. Taking Eyring s transition state theory into account, their results could be formulated using the expression... 

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