Computational Studies of Chiral Epoxide Radicals

Epoxides are strained heterocycles that are common commodity chemicals and synthetic intermediates. The goal of this study is to understand and compare the reactivity of simple epoxides and their radicals in the gas phase using G4 and W1BD calculations. The epoxides include the parent oxirane and monosubstituted analogs having -CH₃, -NH₂, -OH, -F, and -Cl substituents. The C-H bond dissociation energies to form carbon radicals from the various epoxides are reported. Radicals generated on the epoxide ring are nonplanar, and a substituent on the radical carbon has a strong influence on the barrier to invert the radical carbon. Epoxide radicals undergo a competitive ring-opening reaction to form vinoxy radicals, and this process is also influenced by substituents. Calculations on polyfluorinated epoxide radicals were completed, and the barriers to both reactions are elevated in the perfluoro case. These results are largely unchanged when solvent, as incorporated using a polarized continuum model, is included in the calculation. Comparisons to cyclopropyl systems are also made.