Complete assignment and additivity rule for 1H and 13C chemical shifts of non‐planar, nonacyclic aromatic hydrocarbons

Abstract

AbstractComplete assignments of 1H and 13C NMR spectra were made for heptacyclic peropyrene and five isomers of dibenzoperopyrenes, using 2D correlation spectroscopic techniques of homonuclear HH‐COSY and NOESY and heteronuclear CH‐COSY and HMBC methods. New additivity rules of 1H and 13C chemical shift values were established for compounds having two types of benzene ring condensation. All 1H chemical shifts were satisfactorily interpreted by a very simple magnetic point dipole model. This model includes net contributions from each constituent benzene ring due to the ring current anisotropy and permits some ring planes to deviate from the mean molecular plane. The conjugated ring currents are consistent with the chemical shifts. Thus, the aromatic properties are normal even if the molecular skeleton is considerably deformed and becomes non‐planar.