| Abstract
| - We have carried out a G3(MP2) investigation of the enthalpies of formation, isomerization, and hydrogenation(ΔfH298, ΔisomH298, and ΔhydH298), in the gaseous state, of 30 hydrocarbons related, directly or indirectly, to[3]-radialene (tris(methylidine)cyclopropane). The thermochemistry of [3]-radialene and many of the othermolecules presented here is dominated by molecular strain. We have discussed the use and limitations ofseveral methods of obtaining an estimate of strain energy (enthalpy). Despite its extraordinarily high ΔfH298,[3]-radialene (an isomer of benzene) appears to be slightly stabilized by its radial methylene groups, inopposition to the large destabilization brought about by ring strain. Exocyclic conjugative stabilization maybe present in an amount less than 5 kcal mol-1, but it is difficult to quantify because there is no rigorous wayof separating enthalpic effects due to strain from those due to electron conjugation in these calculations.
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