The optimized minimum-energy geometries of the four smallest cyclic amines—aziridine (C2H5N), azetidine (C3H7N), pyrrolidine (C4H9N), and piperidine (C5H11N)—were determined using ab initio methods and density functional calculations. The heats of formation of above-mentioned compounds were calculated using isodesmic reactions and known heats of formations of other compounds in the reactions. Proton affinities were calculated for the compounds using the same calculation methods that were used for calculation the heat of formation. The methods varied in their ability to calculate accurate ΔfH’s, with MP2 calculations being the most accurate and HF calculations the least. Most methods were able to predict the proton affinities well, typically to within 30kJ/mol (or about 5%).