By Warren J Hehre
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Additional resources for A Guide to Molecular Mechanics and Quantum Chemical Calculations
In general, the lower the activation energy the faster the reaction. ** Such limiting reactions have come to be known as “diffusion controlled” reactions. The product formed in greatest amount in a kinetically-controlled reaction (the kinetic product) is that proceeding via the lowest-energy transition state, irrespective of whatever or not this is lowest-energy product (the thermodynamic product). * In addition to temperature, the “rate constant” also depends on pressure, but this dependence is usually ignored.
In practice, this account is based on an “exact” solution for an idealized system, and is introduced using empirical parameters. As a class, the resulting models are referred to as density functional models. Density functional models have proven to be successful for determination of equilibrium geometries and conformations, and are (nearly) as successful as MP2 models for establishing the thermochemistry of reactions where bonds are broken or formed. Discussion is provided in Section II. The Hartree-Fock approximation also provided the basis for what are now commonly referred to as semi-empirical models.
On the other hand, molecular properties resulting from solution of approximate Schrödinger equations would not be expected to be identical to experimentally-determined quantities. In fact, different approximations will lead to different results. * It might be anticipated that the less severe the approximations which make up a particular theoretical model, the closer will be its results to experiment. To the extent that it is possible, any theoretical model should satisfy a number of conditions.
A Guide to Molecular Mechanics and Quantum Chemical Calculations by Warren J Hehre