The solution-phase reactions of microwave-generated hydrogen atoms with terminal olefins is regioselective. Since addition is to the terminal end of the olefin, the reaction yields a secondary radical which undergoes either reaction with molecular or atomic hydrogen, disproportionation, combination, or addition to another olefin, and in the case of hydrogen atom addition to 1,6-heptadiene, cyclization. The cyclized radicals are formed reversibly, and the final product mixture contains only minor amounts of cis-1,2-dimethylcyclopentane (the product of kinetic control) while the major cyclized product is methylcyclohexane. Although an equilibrium mixture could not be obtained, the dimethylcyclopentyl and 3-methylcyclohexyl radicals were shown to be formed reversibly.