A radical is a reactive intermediate with a single ___ electron, formed by ___ of a covalent bond. Allylic radicals are stabilized by, making them ___ stable than tertiary radicals. A compound that contains an especially weak bond that serves as a source of radicals is called a radical . Treatment of cyclohexene with N-bromosuccinimide in the presence of light leads to___ by ___ intermediates. The stability of a radical as the number of alkyl groups bonded to the radical carbon increases. Although alkanes undergo radical substitution reactions with both Cl_2 and Br_2 chlorination is ___ than bromination. A compound that prevents radical reactions from occurring is called a radical ___ Treatment of cyclohexene with bromine in an organic solvent leads to ___ by ___ intermediates. Radical halogenation reactions occur racemization at a stereogenic center.