STRUCTURES AND ENERGIES OF CUMULENE CARBENES

Ab initio calculations have been used to predict structures and relative energies of propadienylidene, propargylene, butatrienylidene, ethynylyinylidene, transoid bivinylidene, and diacetylene. Some understanding of the accuracy of the predictions is obtained from extensive SCF and correlated calculations on vinylidene and acetylene. The energies of H2C2, H2C3, and H2C4cumulene carbenes compared to methylene-like or stable rearrangement structures differ significantly. However, the energies of two different cumulene carbene structures of H2C4, butatrienylidene and ethynylyinylidene, are essentially the same. Electron correlation effects on the relative energies were found to be important, but do not change the qualitative predictions from uncorrelated treatments. The method of self-consistent electron pairs (SCEP) was used to determine correlation energies for these large systems and the largest wave function variationally included 120499 symmetry-adapted configurations. © 1979, American Chemical Society. All rights reserved.