We characterized four prototypical Cvetanović diradicals, C 2 H 4 O, C 3 H 6 O, C 2 H 2 O, and C 3 H 4 O, with an emphasis on the electronic structure aspects relevant to the ISC rates. We found that methylation has a relatively small effect on the electronic structure. In contrast, the diradicals derived from double-and triple-bond unsaturated hydrocarbons are very different.