Quantum chemical calculations and studies have been made on the different spin statesof unsaturated carbenes X_2C=C: and X_2C=C=C:(X=H, Li, F). The geometries and relativestabilities of these carbenes with various groups X have been outlined. The ground states of unsaturatedcarbenes are all singlet. The energy splittings between the ground states and first excited states E(~1A_1-~3B_1) are generally within the value of 60 kcal/mol and change greatly with the electronegativitiesof groups X, but little with the sizes of the cumulidenes. The equilibrium conformations of ~1A_1and ~3B_1 are different. Quantum chemical calculations and studies have been made on the different spin states of unsaturated carbenes X_2C = C: and X_2C = C = C: (X = H, Li, F). The geometries and relative performance of these carbenes with various groups X have been outlined The ground states of unsaturated carbenes are all singlet. The energy splittings between the ground states and first excited states E (~ 1A_1- ~ 3B_1) are generally within the value of 60 kcal / mol and change greatly with the electronegativities of groups X, but little with the sizes of the cumulidenes. The equilibrium conformations of ~ 1A_1and ~ 3B_1 are different.