A computational study of tetrahedrene at the RCCD/cc-pVDZ level led to a singlet-state structurewith a lowest energy vibrational mode of 660 cm-1. The corresponding triplet state was found to beca. 37 kcal/mol lower in energy than the singlet state. The heat of formation of the singlet statewas estimated to be 270 kcal/mol. An isomeric singlet bicyclic dicarbene bis-bicyclo[1.1.0]cyclobutylidene was found to be ∼94 kcal/mol lower in energy than tetrahedrene.