In this collaborative project, still in the preliminary stages, we propose to critically investigate issues of structure and reactivity with a focus on cyclopropane and four related compounds involving hetero-atom substitutions: ethylene oxide (oxirane), thiirane (ethylene sulfide), aziridine, and N-methyl-aziridine. Future work involves the investigation of reactivity and kinetics of the radical cations of the four related compounds with a suite of probe molecules that would provide evidence of the nature of the reactant radical cation. Preliminary theoretical calculations by ab initio methods indicate the similarity of the radical cations of cyclopropane, ethylene oxide, and the aziridines and that thiirane radical cation is divergent and would be expected to exhibit different reactivity. This project involves the resource in a role of expanding the knowledge-base of ion-molecule reactions.