[pmoc]

Regarding the stabilities of free radicals my textbook says the "energy required to break the C-H bond is at the greatest for a methyl carbon, and it decreases for a secondary carbon, and tertiary carbon. The more highly substituted the carbon atom, the less energy is required to form the free radical. We conclude that free radicals are more stable if they are more highly substituted." I get that this makes forming a secondary or tertiary carbon easier than a methyl carbon however I don't get how that implies that a tertiary carbon would be more stable. it In fact, isnt the fact that the methyl carbon and H bond require more energy to break imply that their bond is more stable?

[MrTeo]

In fact, isnt the fact that the methyl carbon and H bond require more energy to break imply that their bond is more stable?

We're talking about stability of radicals, what you said regards the stability of the C-H bond. It is true that the energy of a C-H primary bond has the highest value, but this tells you only that, if compared to other carbons, it's much more difficult to transform a primary C into a radical, while the process is easier for secondary and tertiary carbons. A high bond energy means a low potential energy and this tells us that a free CH₃• radical will quickly take an hydrogen atom from another compound to reach its favored energetic state. The same thing happens with secondary and tertiary carbons, but these, if compared with primary carbons, are less likely to return to their original states (to reach a greater stability) as they don't have the same stability as CH₄ (and their bonds aren't that strong).

If you want to take a deeper peek into this topic try to google "Hyperconjugation"