This process is promoted by captodative ethylene groups before [2+2] (“two-plus-two”) cycloaddition reactions. Mercury lamps induce this process in nitrite esters during the first step of the Barton reaction. A rare intracellular form of this process is the first step of the methylmalonyl-CoA mutase reaction mechanism that requires vitamin B12 cofactors. (-5[1])Evolution of nitrogen gas promotes this process in AIBN (“A-I-B-N”), which precedes hydrogen atom abstraction for one method of polymerization initiation. This process occurs after hydrogen peroxide is exposed to heat or light due to weak oxygen–oxygen bonds. Fishhook arrows are used to depict this process, which usually generates free radicals. For 10 points, name this type of bond cleavage in which each atom involved receives one electron. ■END■ (10[1])