Possible C20 Isomers Containing 4/6 Rings. As Ami Investigation of the Stability of Three 4/6 Cages and of Their Hydrogenated Analogues

Semiempirical AM1 calculations on isomers (I-III) of C₂₀ constructed from six and four-membered rings reveal high enthalpies of formation compared to the dodecahedral or the planar cyclic isomers. Hydrogenation of I-III however reduces greatly their enthalpies of formation and increase the HOMO-LUMO differences making such species interesting targets for synthesis.