Computational Studies of Chiral Epoxide Radicals

TL;DR

This study uses computational methods to explore how substituents affect the reactivity of chiral epoxide radicals in gas and solvent environments.

Contribution

The novel contribution is the computational analysis of substituent effects on epoxide radical reactivity and ring-opening barriers.

Findings

Substituents strongly influence the inversion barrier of radicals on the epoxide ring.

Polyfluorinated epoxide radicals show elevated reaction barriers for ring-opening.

Solvent effects have minimal impact on calculated reaction barriers.

Abstract

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.

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