Molecular dynamics simulations using an empirical bond order potential have been performed to investigate shock-induced chemistry in solid acetylene, ethylene, and methane. Acetylene was found to undergo significant polymerization reactions for flyer plate impact speeds above 10 km/s. These conditions are similar to those which would be experienced upon planetary impact of comets, which are known to contain condensed-phase acetylene. Ethylene exhibits similar reactivity above 15 km/s. Methane undergoes hydrogen abstraction reactions at flyer plate impact speeds of 16-20 km/s and produces hydrocarbon chains at higher impact speeds. The latter results are significant for elucidating the fate of atmospheric methane upon cometary or meteor impact, and for predicting the initial reaction steps in the reactivity of methane ices in the high-pressure, high-temperature interiors of Neptune and Uranus. (C) 2003 American Institute of Physics.