The thermal chemistry of C-6 cyclic hydrocarbons (cyclohexane, cyclohexene, benzene, 1,3- and 1,4-cyclohexadienes, 1-methyl-1-cyclohexene, and toluene) and halo hydrocarbons (iodo cyclohexane, iodo benzene, and 3-bromo cyclohexene) on Ni(100) surfaces has been studied under ultrahigh vacuum conditions by using temperature-programmed desorption (TPD). Cyclohexane was found to only desorb molecularly from the surface, but this is because of the dynamic nature of TPD experiments, and Is therefore not an indication of the inability of nickel to activate the adsorbed molecules. Indeed, cyclohexyl groups, which are the first expected intermediates after the initial C-H bond scission and which were prepared via the thermal treatment of adsorbed iodo cyclohexane, were shown to undergo a facile beta-hydride elimination step to yield first cyclohexene and ultimately benzene, and to concurrently follow a reductive elimination path with surface hydrogen to produce cyclohexane. Cyclohexene was found to dehydrogenate easily to benzene and to not hydrogenate to any significant extent even if atomic hydrogen is present on the surface (again, because the dynamic nature of TPD favors molecular desorption instead). The allylic intermediate expected to form during the dehydrogenation of cyclohexene to cyclohexadiene was prepared by thermal decomposition of 3-bromo cyclohexene and studied by TPD as well, and the remaining hydrogenation and dehydrogenation steps were probed by characterizing the thermal chemistry of the other compounds listed above.