Nuclear magnetic resonance and electron absorption studies of acenaphthylene dianion. Ion-pair structure and charge distribution

Abstract

The ¹H and ¹³C n.m.r. chemical shifts of acenaphthylene dianion are studied by variation of cation, solvent, and temperature. For the description of the charge distribution, comparisons are also made with the neutral hydrocarbon, acenaphthylene. In the contact ion pair structure, the cations occupy nonequivalent positions relative to the dianion. The ability to undergo solvation also differs for the two cations. The Na and K salts exist solely as contact ion pairs under the investigated conditions. ⁷Li N.m.r. and u.v.–visible spectroscopic characterization provide further evidence for the proposed ion pair structures. The comparatively small and variable ¹³C chemical shift–charge correlation factor of the dinegative–uncharged compounds is discussed in view of a varying degree of diatropicity. The electronic structure of the dianion is best described in terms of a partly localized π-electronic system.