# How do you decide the stability of carbon free radical?

$b e n z y l > a l l y l \ge {3}^{\circ} > {2}^{\circ} > {1}^{\circ} > m e t h y l$
Allyl and benzyl radicals are stabilized by resonance with the $\pi$ system; tertiary and secondary radicals are possibly stabilized by hyperconjugation. Interestingly, I was once told by an organic prof that as the percentage s character of the $C - H$ bond increases, the stability of the radical decreases , i.e. $s {p}^{3} > s {p}^{2} > s p$; i.e. acetylenic radicals should be the least stable.