Reaction centre accessibility. I. Calculation of reaction centre congestion and influence of structure flexibility

The fate of a reaction depends on many factors like the electronic reactivity of the ground state molecules, conformation/configuration needs and solvent influence. It is often impossible to predict with any certainty the result, in terms of yield and products, of the interaction between two reactants. Thus the role of reaction centre accessibility is definitely determining but is itself difficult to determine. Nevertheless, within the framework of reaction product prediction it is essential to search for an acceptable solution of predictive modelling. A new approach to both the calculation of steric congestion near reaction centres and its regulation is presented as a first step towards the prediction of centre accessibility. The approach is based on a two dimensional representation of molecules and on the calculation of the steric congestion of each branch, calculated by means of intersecting circles that indicate the extent of the reactivity space and the congestion space.