Radicals: Electronic Structure and Geometry

As with a lone pair, the unpaired electron influences the geometry at the radical center.

Trivalent carbon-centered radicals typically have a superficial pyramidal geometry, with the methyl radical being fully trigonal planar.

In comparison, trivalent sp²-hybridized carbocations are trigonal planar, while sp³-hybridized carbanions are trigonal pyramidal.

While the methyl radical is planar like the former, the CF₃ radical is closer to the latter. So, the trivalent radical structure with one nonbonding electron falls partway between the geometries of carbocations and carbanions.

The chirality of the species is a good indicator of the geometry. A carbanion may be chiral since the pyramidal inversion is difficult.

However, superficially pyramidal carbon-centered radicals are nearly planar, as they readily undergo pyramidal inversion, making such radicals achiral.