The theoretical structures of cyclopropene, 1-methylcyclopropene, 1,2-dimet
hylcyclopropene, and 3,3-dimethylcyclopropene optimized at the HF/6-3 1G* l
evel are juxtaposed with the available experimental data. Some rules govern
ing geometric parameter variations in this series of molecules and related
molecular characteristics are discussed.