The kinetics of the thermal decomposition of normal paraffin hydrocarbons IV. Modes of rupture of the carbon chain

The decomposition of a normal higher paraffin yields methane, ethane and propane in proportions which indicate approximately the relative probability of rupture of the carbon chain at various places. In the nitric oxide-inhibited reaction (by hypothesis, a molecular reaction) these proportions are found to be independent of temperature and pressure over ranges where marked changes would occur if the rupture of the various C—C bonds corresponded to processes of appreciably different activation energy. The variation with pressure of the overall activation energy (part III) is therefore not associated with these various modes of rupture of the molecule. The relative probability of rupture decreases with distance from the end of the carbon chain, methane and ethane being the predominant saturated products. A tentative explanation is suggested, which depends upon the electronic symmetry of the structures of the two lowest paraffins. The proportions of the products formed in the radical chain reaction and in the reaction inhibited by nitric oxide (molecular reaction) are very similar, and an explanation of this fact is offered.