How would the free-radical addition of Br-Br to cyclohexene compare to the non-free radical addition? (Under free-radical conditions, Br2 will substitute an allylic hydrogen rather than add to C=C. NBS is even a better reagent for free radical halogenation. - GS). Why does it substitute an allylic hydrogen instead of adding to the C=C? (Because abstraction of an allyl hydrogen leads to a stable allyl radical, so the reaction pathway shifts to the more favorable substitution over addition. Some addition still takes place, and this is suppressed by using NBS instead of Br2. - GS).