Elusiveness of Bishomoaromaticity in Anionic Systems : The Bicyclo [ 3 . 2 . 1 ] octa - 3 , 6 - dien - 2 - yl

  • Published 2001

Abstract

The electronic structure of the bicyclo[3.2.l]octa-3,6-dien-2-yl anion (6), considered to be the prototype bishomoaromatic anion, was analyzed by semiempirical (MNDO) and ab initio (STO-3G) MO calculations. No evidence for homoaromatic stabilization (i.e., cyclic delocalization) was found. C-2-C-7 distances and Mulliken overlap populations between these carbons are almost identical in the 6~ anion 6 and the corresponding 457 cation 7. The calculated stabilization energy of anions 21 and 24 is similar to that of the alleged homoaromatic species 6 even though the orientation of the additional double bonds in 21 and 24 does not permit homoconjugative interaction with the allyl HOMO (eq 1, 3, 5 ) . The experimentally observed stabilizing effect of the C-6-C-7 double bond in 6 is due to an inductive effect. In general, homoaromatic stabilization is not expected to be an important phenomenon in anions. Applequist and Roberts recognized the unusual stability of the cyclobutenylium ion (l).I The geometry of the small ring fa-

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@inproceedings{2001ElusivenessOB, title={Elusiveness of Bishomoaromaticity in Anionic Systems : The Bicyclo [ 3 . 2 . 1 ] octa - 3 , 6 - dien - 2 - yl}, author={}, year={2001} }