title: Quantum mechanical designs toward planar delocalized cyclooctatetraene: a new target for synthesis.
abstract: Ab initio and hybrid density functional quantum mechanical computation are applied to the structure and energetics of a series of annelated cyclooctatetraenes. Tetrakis-cyclobuteno, perfluorocyclobuteno or bicyclo[2.1.1]hexeno annelations result in planar structures with distinct exo and endo valence tautomers of the double bonded cycle. The contribution of each basic annelation to the exo/endo relative energy is estimated. An additivity scheme for approximating the energy of a mixed system is developed and compared to the quantum mechanical prediction. Bis bicyclic annelation to the a and d positions creates "valence tautomeric frustration" and strongly perturbs the molecular structure. This phenomenon leads to a general design for a planar cyclooctatetraenes where the "delocalized" diradicaloid state is the minimum energy form. These compounds are seen as excellent targets for chemical synthesis.
authors.affiliation: San Diego Supercomputer Center, La Jolla, California 92093-0505, USA.
authors.forename: K K
authors.initials: KK
authors.lastname: Baldridge
authors.forename: J S
authors.initials: JS
authors.lastname: Siegel
mesh_terms: D000475:Alkenes; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D000475:Alkenes