[Billqaz3]

Show how free radical halogenation might be used to synthesize the following compounds. In each case explain why we expect to get a single major product.

b) 2-bromo-2-methylbutane

I have the mechanism figured out but what I can't figure out is why we expect to get a single major product as far as I can tell the only reason why that might be is that the second C is highly substituted making the reactive intermediate more stable. But to me that seems like a flimsy reason to base my answer on.

[kriggy]

Well that is the case, the tertiary radical willl be more stable. Being major product is very vague description IMO it could be anywhere from 99% vs 1% to like 40% vs 12x5%

[orgopete]

Well that is the case, the tertiary radical will be more stable.

I am troubled by this kind of argument. If the reaction were completely reversible, then I can understand this reasoning. If this is essentially a kinetic reaction (which I think it is), then I don't see how this should apply.

[Enthalpy]

In free-radical bromination, the step creating a radical needs help from heat. Much help, for instance 10 times kT, so this step happens very uncommonly. A radical that needs even more help, especially at a primary carbon, is much more unlikely to happen, and the corresponding product is rare.
http://people.chem.ucsb.edu/neuman/robert/orgchembyneuman.book/11%20RadicalSubstitutionAddition/11FullChapt.pdf