SINGLET-TRIPLET GAP IN 1,2,3-BUTATRIENE AND ITS CONSEQUENCES ON THE MECHANISM OF ITS SPONTANEOUS POLYMERIZATION

The reactivity of 1,2,3 butatriene, C4H4, has been postulated to be du e to the presence of low-lying triplet states. However, there have bee n no experimental or theoretical determinations of the energy separati ons or geometries of these states. We have examined the structures, en ergetics, and possible mechanisms involved in the self-polymerization of the title compound using single-determinant ab initio molecular orb ital theory. We find that the magnitude of the singlet-triplet gap for the monomer and its relatively high positive heat of formation does n ot allow for a mechanism involving the direct formation of an isolated triplet species. We speculate on an alternative mechanism and show it s relationship to recent work on related reactive monomers.