13C NMR of polycyclic aromatic compounds. A review

Abstract

AbstractThe analysis of the 13C NMR spectra of polycyclic aromatics is discussed briefly. Basic trends of chemical shifts are mentioned, but the emphasis is placed on substituent‐induced chemical shifts (SCS). Semi‐empirical approaches and regressional analysis are treated. The factors controlling SCS are discussed and steric, mesomeric and π‐inductive effects are analysed.CH, CF, CC, CP and C, Metal coupling constants are investigated and the influence of steric effects, bond order, mesomerism and angle distortions in relation to some of these coupling constants is discussed. Relaxation times are described in a series of compounds. The effects of dissolved oxygen or radicals are shown and the use of T1 as a monitor of molecular tumbling is depicted. The impact of 13C NMR on the understanding of charged aromatic species, both positive and negative ions, is mentioned and new information about reaction intermediates in electrophilic aromatic substitution is outlined. The possibility of using 13C NMR to investigate charge transfer complexes is also discussed. Among other subjects treated are automerization, deuterium exchange and biosynthetic incorporation of labelled materials and, finally, quantitative analysis is briefly touched upon.