Chemical Shifts in C₅H₅^-, C₆H₆ and C₇H₇⁺; Chemical Shifts and π-Electron Densities¹

Abstract

The chemical shifts of several salts and derivatives of the cyclopentadienyl anion C_5H_5^- and the tropylium cation C_7H_7^+ have been determined relatived to benzene as an internal standard in dimethyl sulfoxide and acetonitrile. The observed shifts are +1.85 and - 1.9 p.p.m. for C_5H_5^- and C_7H_7^+, respectively. These shifts are mainly accounted for by the electrostatic interaction between charge localized in the π-orbital oE a carbon atom and the electrons in the C-H bond. The results, in conjunction with their theoretical interpretation, are used to determine "experimental" charge distributions in other aromatic systems.