MRCI and CASPT2 calculations from a (4, 4) MCSCF active space predict both vinylnitrene and vinylphosphinidene to have 3 A ground states. For vinylnitrene, the lowest open-shell singlet ( 1 A ) and closed-shell singlet ( 1 A ) states lie 15 and 40 kcal/mol higher in energy, respectively. The corresponding relative singlet energies in vinylphosphinidene are 17 and 23 kcal/mol, respectively. The reduced separation between the singlet states in H 2 C=CHP compared to H 2 C=CHN is attributed to decreased conjugation between the double bond and the pnictogen atom in the phosphinidene.