The methane combustion inhibitor CCl4 exerts no effect on the first ignition limit of hydrogen; therefore, the role of hydrogen atoms in hydrocarbon oxidation consists at least of participating in longer reaction chains than are observed in hydrogen oxidation. The upper limits of the rate constants of the reactions of hydrogen atoms with propylene and isobutylene molecules were estimated by the self-ignition limit method to be (1.0 ± 0.3) × 10−11 exp(−1450 ± 400/T) and (0.8 ± 0.3) × 10−11 exp(−550 ± 200/T) cm3 molecule−1 s−1, respectively, in the temperature range of 840–950 K. These data are evidence that the stronger inductive effect of the two methyl groups in isobutylene lowers the energy barrier to the H + iso-C4H8 reaction. It has been demonstrated experimentally that chemiluminescence in the hydrocarbon flame front at atmospheric pressure precedes heat evolution. Throughout the pressure and temperature ranges examined (5–750 Torr, 298–950 K), the chain mechanism determines the basic laws of combustion.