Application of the Mechanical-Chemical Analogy to Predict the Reaction Mechanisms and Pathways of Thermal Degradation

Reaction mechanisms concerning thermal degradation of organic materials and in chemistry in general are usually proposed on the base of stable products and intermediates found by suitable methods of chemical analysis. It happens that not only species that have been proved by chemical analysis, but also merely postulated intermediates are included in an elegant reaction scheme. Frequently such creatures rely more or less on the intuition and certain qualitative rules that are state of the art. In the paper a simple method is developed to calculate the energies of intermediates along an assumed reaction co-ordinate. The calculation is based on van Krevelen ́s method of increments. The energy profile along the reaction co-ordinate is utilised to judge about various proposed reactions mechanisms. A particular reaction mechanism is believed to be unlikely, if its intermediates would have high energy content in comparison to those postulated in another reaction path. In this way the calculation of the energy profile may be used to discriminate proposed reaction mechanisms. The idea is exemplified with initial stages of the degradation of polystyrene.