Abstract ET spectroscopy was applied to measure the electron affinities of 3-methyl-3- t-butyl-cyclopropene, 3-methyl-3-(3,3-dimethylbutynyl-1)cyclopropene, and bis(1-methyl-2-cyclopropenyl)acetylene. The electron affinities are discussed in relation with the previously measured ionization energies within the context of Koopmans' theorem and striking asymmetries are found in the arrangement of the filled and unfilled orbitals. The highest occupied orbital in the latter two compounds is the acetylenic π MO, the lowest unoccupied the ethylenic π* MO. The cyclopropenyl substituent leads to sizeable splitting (≈ 0.5 eV) of the acetylenic π MOs. In contrast, the splitting of the acetylenic π* MOs is too small (<0.2 eV) to be observable. The possible implications of the results on chemical reactivity are discussed.