Energy controlled rate constant

In liquids, collisional energy transfer takes place by multistep diffusion (the rate determining step) followed by an exchange interaction when the pair is very close. The bimolecular-diffusion-controlled rate constant is obtained from Smoluchowski s theory the result, including the time-dependent part, may be written as... 

Energy-resolved rate constant measurements near the threshold for diplet methylene formation from ketene have been used to provide confirmation of the fundamental hypothesis of statistical transition state theory (that rates are controlled by the number of energetically accessible vibrational states at the transition state).6 The electronic structure and aromaticity of planar singlet n2-carbenes has been studied by re-election coupling perturbation theory.7 The heats of formation of three ground-state triplet carbenes have been determined by collision-induced dissociation threshold analysis.8 The heats of formation of methylene, vinylcarbene (H2C=CHCH), and phenylcarbene were found to be 92.2 3.7, 93.3 3.4, and 102.8 33.5 kcal mol-1, respectively. 

As mentioned in the very beginning, at low free energies of the electron transfer reaction (AH < 0.6 eV), activation-controlled rate constants... 

Similarly, many people have used the concept of localization energy to account for the rates, and sites, of electrophilic substitution. The localization energy is a calculated value of the endothermicity in a reaction and is therefore part of an argument based on product development control. The plot of localization energy against rate constant is also a good straight line.60 This is no place to try to estimate the relative success of these two approaches they are obviously related in some deep-seated property of molecular orbitals.61... 

Since the reaction of Inh with the radicals has a low activation energy, is a diffusion-controlled rate constant for the reaction (about 10 lmol s depending on the viscosity of the melt) and thus, even for low concentrations of inhibitor, v 1. The oxidation rate, given by rp, will be very low until [Inh] < Ap[RH]/ ki and thereafter the oxidation will proceed as if there were no additive. This is shown schematically in Figure 1.41(a), and it may be seen that the induction period increases with the concentration, C, of inhibitor. If... 

Absolute rate constants have been determined for aromatic triplet formation in acetone solutions of several aromatic compounds (5, 30). The formation curves were observed directly for anthracene and naphthalene triplet (5) and for diphenyl triplet. These rate curves were found to fit a first order rate law, and were interpreted as a bimolecular energy transfer process from a state of the solvent molecule which is probably the triplet, that is, by Reaction 11. These rate constants, as well as the triplet yields, are listed in Table VI. The rate constants for anthracene and naphthalene triplet formation appear to correspond to diffusion controlled rate constants. Two further points are of interest, which are in contrast with observations in other systems which will be discussed. In acetone, most of the yield of aromatic triplet (at concentrations of the aromatic compound of 5 X 10"3M or lower) is formed in diffusional processes such as collisional energy transfer. Any fast formation appears... 

Bimolecular association rate constant Rate constant for dissociation Rate constant for Dexter energy transfer Rate constant for diffusion-controlled reactions Rate constant for fluorescence... 

Table 6.3 Rate constants for some donor-acceptor reactions of aromatic hydrocarbons with amine bases in acetonitrile, 3 is rate constant (M s ) at temperature T for reaction A - - D A + D+ /to s theoretical diffusion-controlled rate constant io = 4RT/r] (M s ). 3, Eq are the Arrhenius activation energies corre-...

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