Rate constants isomerization

Garrity D K and Skinner J L 1983 Effect of potential shape on isomerization rate constants for the BGK model Chem. Phys. Lett. 95 46-51... 

A reaction mechanism in which the ( )-diazoate is formed by attack of the diazonium ion by a hydroxide ion in such a way that the ( )-diazoate is the primary intermediate (i. e., reaction sequence 6 - 3 in Scheme 5-14) is not consistent with the observation that the isomerization rate constant is independent of the hydroxide ion concentration. 

Non-Arrhenius behavior of the isomerization rate constant of sterically hindered aryl radicals 2,4,6-triterbutylphenyl... 

D. Shen and H. O. Pritchard, ]. Chem. Soc., Faraday Trans., 92,4357 (1996). Randomization and Isomerization Rate Constants for Isocyanogen. 

Figure 28. Simulated para selectivity y°ut at the reactor outlet as a function of the isomerization rate constant k. Dependence on the ratio of effective diffusivities RD = Dpj /D c.

The simulation results also show that the product shape-selective effect does not depend on the inlet concentration of EB, nor on the rate of the disproportionation reaction (i.e. the rate constant ky). Instead, it is affected by the ratio of the catalyst weight, divided by the total flow rate, mKM/q, which may be interpreted as a modified residence time. This is illustrated in Fig. 29, where the para selectivity is plotted against the isomerization rate constant for different values of m[Pg.364]

A reduced residence time leads to an increase of the para selectivity. However, at the same time the conversion drops, and thus the para concentration at the reactor outlet is reduced. In addition, the maxima of the curves shown in Fig. 29 become less distinct. In the limiting case of zero conversion, the para selectivity increases steadily with increasing values of the isomerization rate constant. Then a maximum is no longer observed. This is exactly the result obtained by Wei [107]. However, it is true only for small conversions. As soon as the conversion increases, the assumption of a... 

The effect of different adsorption constants of the isomers is illustrated in Fig. 31 where the para selectivity is plotted against the isomerization rate constant for different ratios of the adsorption constants Rk = KP/E (K = Km = const.). From this we note that the maximum para selectivity increases as the adsorption constant of the para isomer is reduced below the respective constants of the other isomers. This effect is most pronounced at large values of k. Moreover, when the ratio of the adsorption constants Rn tends to zero, the para selectivity increases steadily with increasing values of... 

Finally, in Fig. 32 the influence of the primary isomer distribution on the observable para selectivity is shown by plotting the para selectivity versus the isomerization rate constant for different primary isomer distributions. 

Isomerization Rate Constants for Symmetric Double-Well Potential Systems Defined in Table XIV... 

Isomerization Rate Constants for Systems No. 7 and No. 8 Obtained from Trajectory Calculations, RIT, the Transition State Theory (TST), and the MRRKM Theory... 

A few of these cases were studied within the framework of RIT by DeLeon et al. [59] for energy = 0.58, 0.75, and 1.00. The isomerization rate constants calculated from the MRRKM theory are in very good agreement with those obtained from trajectory calculations and with those calculated from RIT. This comparison is given in Table XIX. Interestingly, both the MRRKM theory and RIT more or less overestimate the rate of isomerization when compared to the trajectory calculations. 

The Isomerization Rate Constants in a Model Three-Well Potential, Obtained from MRRKM, Trajectory Calculations, and RIT... 

MRRKM theory, from RIT, from direct trajectory simulations, and, for reference purposes, from the RRKM theory. In particular, a test of the effect of the RRKM choice of transition state on the predicted rate of isomerization is made by neglecting the contribution of intramolecular energy transfer (Model No. 1). It is seen that the RRKM choice of transition state leads to considerable error the isomerization rate constant predicted is greater than those from the MRRKM theory and RIT by as much as a factor of 4. With intramolecular bottlenecks taken into account, both RIT and the MRRKM theory agree well with trajectory calculations. 

The Classical Isomerization Rate Constants of Cyclobutanone from the RRKM Theory, Gray-Rice theory, MRRKM Theory, and Trajectory Calculations (in 10 a.u.)... 

Fig. XI.3. Pressure dependence of a unimt)lecular isomerization rate constant.

The effect of temperature on the over-all isomerization rate constant was determined using Equation 2. The temperature range was from 400° to 500°F all other conditions were held constant. An activation energy of 35.5 dz 2.4 kcal/mole was determined from the Arrhenius-type plot shown in Figure 2. Values of 30 (4) and 35.4 (5) kcal/mole have been reported for temperature ranges of 600°-700° and 700°-800°F, respectively, for WS2 and M0S2 catalysts. The high activity of mordenite relative to these catalysts is apparent. 

To close Section III, we note some experimental results that may relate to the issues just discussed namely, Sumi and Asano [13] have recently attempted to fit the viscosity dependence of isomerization rate constants for... 

These experimental facts and the comparison of the three computational methods suggest these tentative generalizations the use of Eq. (5.195) with CBS-Q or (preferably ) G2 values of AG gives for unimolecular isomerizations rate constants that are qualitatively reliable. The CBS-4 rate constants are smaller than the CBS-Q and G2 ones by a factor of from 2 to 1000. This is not bad for CBS-Q and G2, considering that Eq. (5.195) is quite approximate, and that the CBS and G2 methods (section 5.5.2.2b) were developed to provide reliable thermodynamic data, not to handle transition states. 

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