The Importance of Strain on the Relative Energies of Bridgehead Radicals

Abstract

Bridgehead radicals are increasingly commonly-encountered intermediates in organic chemistry. These carbon-centered radicals, however, may experience unique strain energies due to pyramidalization at the bridgehead carbon as enforced by the bicyclic frameworks. In this study, a series of related bicyclic bridgehead radicals were analyzed using the G3MP2B3 computational protocol. The adamantyl and cubyl radicals were also included in the study. The energies of the radicals were analyzed with reference to the similarly-substituted tert-butyl radical via a hyperhomodesmotic equation. While the relative energies were found to weakly correlate with the change in pyramidalization at the bridgehead carbons upon radical formation, a much stronger correlation was observed with the difference in strain energies between the saturated bicyclic compounds and the corresponding bridgehead radicals.