Alkyl radicals are usually sp2 hybridized. Eg the methyl radical is sp2 hybridized. Sp3 hybridized free radicals would form from bridgeheads incapable of flattening, such as adamantyl. They can be formed, but are less stable.

Simple alkyl radicals prefer a planar shape. For example the methyl radical adopts a planar geometry as shown by ESR spectra and other studies. See. https://www.nature.com/articles/2221123a0 . These are sp2 hybridized. However radicals can also be formed on bridgeheads, which are incapable of planarity. These radicals are harder to form and cam be thought of as sp3 hybridized. See. https://pubs.acs.org/doi/abs/10.1021/ja00048a005 .

Thank you very much for this comment. Aren’t most alkyl radicals shallow pyramidal though?

Glad to hear it Kat!

I think one reasoning could be that of C were sp3 the orbital in which the unpaired electron was resting had some s character and if it were sp2 the electron has pure p orbital which relative further from pure s orbital

This page (and the few before it) have been an unbelievable help :)

Everything is well laid out and sufficiently explained!

Kat

Readily available information. I’d refer you to Carey & Sundberg A, or March’s Advanced Organic Chemistry for further discussion.