Ab initio calculations on the lowest singlet and triplet states of 2,2-difluorocyclopentane-1,3-diyl (2) find that the singlet lies well below the triplet at ail geometries. The planar singlet is the transition state for molecular inversion of 5,5-difluorobicyclo[2.1.0]pentane (4), for which Delta H-double dagger is computed to be 18.3 kcal/mol at the CASPT2N/6-31G* level of theory. The small enthalpy difference between 2 and 4 suggests that the 1,3-diphenyl derivative of singlet diradical 2 should be thermodynamically stable toward ring closure.