Fulvenones and Isoelectronic Diazocyclopolyenes: Theoretical Studies of Structures and Stabilization
نویسنده
چکیده
Isodesmic energy comparisons of 6-31G*//6-31GS calculations for the fulvenes 1-3 and fulvenones 4-6 show significant destabilization for triafulvenone (4, -1 7.1 kcal) and heptafulvenone (6, -5.1 kcal/mol) and stabilization for pentafulvenone (5,4.1 kcal/mol). These effects are attributed to enhanced antiaromatic destabilization in 4 and 6 compared to the corresponding fulvenes and enhanced aromatic stabilization in pentafulvenone (5) compared to pentafulvene (2). Analysis of dipole moments, atomic charges, and bond lengths provides further evidence for these aromaticity effects. Similar evidence is found for antiaromatic destabilization upon fluorine substitution in the exocyclic methylene group of triafulvene. Diazocyclopropene (7), diazocyclopentadiene (8), and diazocycloheptatriene (9) are isoelectronic with the corresponding fulvenones 4-6, respectively, and show the corresponding destabilization and stabilization effects. The fulvenes, especially triafulvene (l), pentafulvene (2), and heptafulvene (3), have attracted intense interest because of their unique conjugated structures.'a-h The question of the aromatic/antiaromatic character of these and similar rings has attracted particular attention.'
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