INVESTIGATION OF THE PYROLYSIS MECHANISM OF OXAZOLE AND MALEIMIDE BY USING THE AM1 AND PM3 METHODS

In order to establish characteristics of heterocycles that could be em ployed as a measure of their thermostability and might be useful in in terpreting the thermostability of polyheteroarylenes, the mechanisms o f the pyrolytic dissociation of oxazole and maleimide were studied usi ng the PM3 and AM1 methods. The decomposition of oxazole yielding .CHC HO. + HCN and two decompositions of maleimide yielding .CHCHCONH. + CO and .CHCHCO. + HNCO, respectively, were studied. In all cases the dis sociations take place via a sequential breaking of two ring bonds; the rate-determining step is the breaking of the second bond. The energet ically favourable sequences of bond-breaking were established. Oxazole dissociation is predicted to take place in a triplet state. Maleimide is predicted to be more stable than oxazole. Both the activation barr ier of the rate-determining step and the heterocycle dissociation ener gy can serve as a measure of the heterocycle stability.