Bond fixation in a [14]annulene: Synthesis, characterization, and ab initio computations of furan adducts of dimethyldihydropyrene

Abstract

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 downfield 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.