The potential energy surfaces for the abstraction reactions of heavy carbenes with oxirane have been studied using density functional theory (B3LYP). Five carbene species, including methylene, CH2; silylene, SiH2; germylene, GeH2; stannylene, SnH2; and plumbylene, PbH2; have been chosen in this work as model reactants. The present theoretical investigations suggest that the relative carbenic reactivity decreases in the order: CH2 > SiH2 > GeH2 much greater than SnH2 > PbH2. That is to say, for oxirane deoxygenations, there is a very clear trend toward higher activation barriers and more endothermic (or less exothermic) reactions on going from C to Pb. More specifically, the theoretical findings strongly suggest that CH2, SiH2, and GeH2 should readily abstract oxygen atoms from oxiranes, while SnH2 and PbH2 are unreactive with oxiranes. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.