Radical Polarity

The polarity of a radical intermediate profoundly impacts
its reactivity
and selectivity. To quantify this influence and predict its effects,
the electrophilicity/nucleophilicity of >500 radicals has been
calculated.
This database of open-shell species entails frequently encountered
synthetic intermediates, including radicals centered at sp3, sp2, and sp hybridized carbon atoms or various heteroatoms
(O, N, S, P, B, Si, X). Importantly, these computationally determined polarities have been experimentally validated
for electronically diverse sets of >50 C-centered radicals, as
well
as N- and O- centered radicals. High correlations are measured between calculated polarity and quantified reactivity,
as well as within parallel sets of competition experiments (across
different radical types and reaction classes). These multipronged
analyses show a strong relationship between the computed electrophilicity,
ω, of a radical and its relative reactivity (krel vs Δω slopes up to 40; showing mere Δω
of 0.1 eV affords up to 4-fold rate enhancement). We expect this experimentally validated database will enable reactivity
and selectivity prediction (by harnessing polarity-matched rate enhancement)
and assist with troubleshooting in synthetic reaction development.