BULLVALENE - REACTION GRAPHS RELATING POLYSUBSTITUTED POSITIONAL ISOMERS

Bullvalene, C10H10, is known to be fluxional as a result of a fast, de generate Cope rearrangement that can move every carbon atom through al l 10 positions in the structural framework. Bullvalene positional isom ers, C(10)H(10-n)R(n), can be made by replacing one or more hydrogens with substituents R. The resulting substitutional isomers are known to undergo rapid isomerization, and over a period of 30 years, Schroder and co-workers have accumulated observations of rearrangements of bull valenes with n = 1-6 identical substituents R. In this paper we presen t reaction graphs that follow the rearrangements of all possible bullv alene positional isomers for substitution n = 1-5. Each vertex in the reaction graph represents an isomer, and each edge stands for a rearra ngement process that interconverts the pair of connected isomers. Thus the reaction graph serves as a road map of the energy surface for the substituted bullvalene system. Reaction graphs can be used to interpr et the observed isomerization data. We report AM1 calculations of heat s of formation of mono- and di-heterosubstituted bullvalene isomers to model relative stability trends of observed substituted isomers.