Role of hydrogen atoms in the pyrolysis of olefinic and aromatic hydrocarbons is discussed with special reference to the hydrogenolysis of propylene and toluene. Hydrogen atoms are shown to serve as chain propagating carrier in the scheme of hydrogenolysis chain, and also to serve as reagent to activate substrate molecules having π-electrons and/or strongly electro-negative atoms. Reaction pathways to form the activated adducts between given substrates and hydrogen atoms, and the fate of the adducts so formed are then presented.Finally, the effect of hydrogen atoms as chemical activator is demonstrated by the hydrogen atom induced coal liquefaction.
