Bond Fixation in a [14]Annulene: Synthesis, Characterization, and ab Initio Computations of Furan Adducts of Dimethyldihydropyrene

Furan adducts, 13, 15, and 16, of
dimethyldihydropyrene are prepared in order to test the postulate
that
bicyclic annelations are generally effective at inducing bond
localization in aromatic systems. A large 2-ppm down-field shift of the 1H NMR shifts of the internal methyl
signals in 15 compared to 16 provides a
significant indicator
of bond localization in 15. X-ray diffraction analysis
of 13 displays regular bond length alternation. Ab
initio
computations that do not include dynamic electron correlation are found
to be inadequate for modeling the molecular
structure of 1. Density Functional Theory models
1 well and predicts bond localization in derivatives of
1 consistent
with the observed NMR spectroscopic and X-ray diffraction
results.