Entropic rate accelerations and orbital steering

The combination of two bromine atoms to form a bromine molecule cannot be used as a model to estimate the entropic loss of more complex bimolecular reactions of biochemical significance. This reaction has an unusually small entropy change because of the development in the product of rotational entropy which is absent in the monoatomic reactants. In general, the formation of a transition state or monomolecular product from two molecules of reactant, in the gas phase, results in the loss of about 15 Kcal.mole−1 of translational and rotational entropy. Effective molarities of up to 108 M can be rationalised in terms of entropy changes without the introduction of new chemical concepts or terms.