Bond length alternation in pentalene

Abstract

According to lcao-mo calculations lower π-electron and total electron energy values result if the molecular symmetry group for pentalene is taken to be C_2h instead of D_2h . Though a considerable reduction in π-electron energy is obtained, the gain in total electron energy is much smaller. Nevertheless it may be stated that in the ground state the twofold axes C₂ ^x and C₂ ^y are not present.