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The Electronic Structures of Aziridenium and Cyclopropylidene. Hypovalent Atoms in Three-Membered Rings

Cramer, C. J.; Worthington, S. E.
J. Phys. Chem. 1995, 99, 1462.

Hartree-Fock, second-order perturbation theory, configuration interaction including single and double excitations, coupled cluster theory including singles, doubles, and perturbative triples, multiconfiguration self-consistent-field, and density functional calculations have been carried out using large basis sets for the 1A1 and 3B1 electronic states of aziridenium and cyclopropylidene. The aziridenium ion is predicted to be a ground state triplet with a singlet-triplet gap of 10.7 +/- 0.4 kcal/mol; the singlet is a transition state subject to ring opening. Isoelectronic cyclopropylidene is predicted to be a ground state singlet with a singlet-triplet gap of -13.8 +/- 0.3 kcal/mol. The optimized aziridenium triplet geometry manifests a remarkably long carbon-carbon bond (1.745Å at the MCSCF level); the corresponding bond distance in cyclopropylidene is also long (1.618Å).

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