Coupled-cluster studies of singlet propynylidene

The equilibrium geometry of singlet propynylidene is studied with high leve l coupled-cluster methods and moderate size to large basis sets. The calcul ations uniformly predict that the equilibrium structure is distorted from t he C-2v 1,3 biradical picture, with CC bond lengths that differ by approxim ately 0.1 Angstrom. Despite this, the barrier calculated for automerization between the two equivalent C-s minima on the potential surface is less tha n 1 kcal mol(-1). Hence, it is likely that experimental studies of singlet propynylidene will be consistent with the dynamically averaged C-2v symmetr y of the molecule.