As a follow-up to a study of dioxadiazetidine, N2H2O2, as a potential high energy density material, we determined optimized geometries, vibrational frequencies, and enthalpies of formation and combustion of its organic derivatives 2-methyl-1,3-dioxa-2,4-diazetidine and 2,4-dimethyl-1,3-dioxa-2,4-diazetidine, both of which would exist as cis and trans isomers. As a fundamental measure of the reactivity of the two compounds, the proton affinities of both isomers were also determined. Gaussian-2, Gaussian-3, and two complete basis set methods were used.