Final answer:
The stability of carbon radicals increases from primary to secondary to tertiary, with tertiary radicals being the most stable due to hyperconjugation and inductive effects. These radicals are sp² hybridized and highly reactive. Resonance stabilization can also enhance the stability if the unpaired electron can be delocalized.
Step-by-step explanation:
The relative stabilities of carbon radicals can be ranked based on the number of alkyl substituents attached to the carbon atom bearing the unpaired electron. Generally, the stability increases in this order: primary (RCH₂) < secondary (R₂CH) < tertiary (R₃C). This trend parallels the stability of carbocations, where the more substituted the carbocation, the more stable it is due to hyperconjugation and inductive effects.
Hence, a tertiary carbon radical is more stable than a secondary or primary one. These radicals are reactive intermediates with three bonds and an unshared electron, usually in a p-orbital, and are thus sp² hybridized. The unshared electron makes these radicals highly reactive as they tend to form a stable covalent bond by sharing the electron.
Resonance can also play a role in the stability of radicals; more resonance stabilization occurs when there are more equal contributors. This means a radical that can delocalize its unpaired electron over several atoms through resonance will be more stable than one that does not have this ability.