Activation energy identity

Shape of potential energy diagram is identical with that for ethane (Figure 3 4) Activation energy for rotation about the C—C bond is higher than that of ethane lower than that of butane... 

This involves a more uniform distribution of charge because of the identical substituents and thus lacks the stabilizing effect of the polar resonance form. The activation energy for this mode of addition is greater than that for alternation, at least when X and Y are sufficiently different. 

The radiation emitted is usually longer in wavelength (i.e. lower in energy) than the incident light (Store s law). It is only in the case of 0—0 transitions (shown in Figure 27 as thick arrows) that the wavelengths for fluorescence and activation are identical. 

Relative reactivity wiU vary with the temperature chosen for comparison unless the temperature coefficients are identical. For example, the rate ratio of ethoxy-dechlorination of 4-chloro- vs. 2-chloro-pyridine is 2.9 at the experimental temperature (120°) but is 40 at the reference temperature (20°) used for comparing the calculated values. The ratio of the rate of reaction of 2-chloro-pyridine with ethoxide ion to that of its reaction with 2-chloronitro-benzene is 35 at 90° and 90 at 20°. The activation energy determines the temperature coefficient which is the slope of the line relating the reaction rate and teniperature. Comparisons of reactivity will of course vary with temperature if the activation energies are different and the lines are not parallel. The increase in the reaction rate with temperature will be greater the higher the activation energy. 

Because the activation energy and preexponential factor for the fuel and oxidizer pyrolysis reactions are not identical, the only way for Eq. (30) to be valid is for Ta t Tf. 

Not only were the reaction rates for bromination by bromine and by hypobromous acid very similar, but the corresponding activation energies (determined over a 20 °C range) were between 11.8 and 12.6 (for Br2) and 12.5 and 12.7 (for HOBr). Thus all this kinetic data is consistent with the rapid formation of an intermediate which is identical for both brominating reagents, and from which the slow loss of a proton subsequently occurs. 

The electronic, rotational and translational properties of the H, D and T atoms are identical. However, by virtue of the larger mass of T compared with D and H, the vibrational energy of C-H> C-D > C-T. In the transition state, one vibrational degree of freedom is lost, which leads to differences between isotopes in activation energy. This leads in turn to an isotope-dependent difference in rate - the lower the mass of the isotope, the lower the activation energy and thus the faster the rate. The kinetic isotope effects therefore have different values depending on the isotopes being compared - (rate of H-transfer) (rate of D-transfer) = 7 1 (rate of H-transfer) (rate of T-transfer) 15 1 at 25 °C. 

Such a pre-equilibrium closely parallels that suggested by Dewar et for the manganic acetate oxidations of several aromatic ethers and amines (p. 405). Other features of the reaction are a p value of —0.7 and identical activation energies of 25.3 kcal.mole for oxidation of toluene, ethylbenzene, cumene, diphenylmethane and triphenylmethane. 

Hydroxybenzoate decarboxylase (EC 4.1.1.61) of anaerobe C. hydroxyben-zoicum was purified and characterized for the first time. ° It has an apparent molecular mass of 350 kDa and consists of six identical subunits of 57kDa. The temperature optimum for the decarboxylation is approximately 50°C, the optimum pH being 5.6-6.2. The activation energy for decarboxylation of 4-hydroxybenzoate is 65kJmor (20-37°C). The enzyme also catalyzes the decarboxylation of... 

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