Of course, much more can be done on a theoretical basis in the calculation of activation energies via computer. Most current methods have as a distant ancestor the treatment of Eyring and Polanyi [H. Eyring and M. Polanyi, Z. Physik. Chem., B12, 279 (1931)]. They considered the problem in terms of the coulombic and [Pg.156]

Several studies [7e, 9, 10, 17] show that the first reaction (ki) is the slow step and thus the activation energy, for production of T(C6)H is the activation energy for reaction 1. Recent theoretical calculations of the barrier to reaction 1 suggest a 0.4 eV (9 kcal/mole) barrier between the base-paired pro- [Pg.107]

The semiempirical nature of the methods used to construct multidimensional potential energy surfaces makes the quantitative validity of the results questionable. Hence the present state of the theoretical calculation of activation energies is unsatisfactory. [Pg.115]

It should be stated at the beginning that despite quite numerous partial successes the present state of the quantum-chemical theory of reactivity is far from satisfactory. First of all, it is not clear whether the present shortcomings are due to the non-adequacy of models of activated complexes or to the drastic approximations made in the calculation of the energy of the activated complex and the reactants. On the other hand, some other deficiencies of most of the reported attempts to interpret reactivity in terms of the theory are obvious the very nature of the HMO method is thought148 to make it necessary to treat as large sets of theoretical and experimental data as possible and, in addition, to respect the distinction in properties of the three classes of positions mentioned (in this connection we do not refer to the difference in the stereochemistry of these positions). [Pg.98]

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