Lanthanide Shifts in the ¹H N.M.R. Spectra of 1,4-Naphthoquinones

Abstract

Lanthanide-induced shifts are discussed for 38 naphthoquinones incorporating a wide variety of substituents. For substrates unsymmetrically substituted in the benzenoid ring the shift reagent leads to spectroscopic differentiation of the quinonoid protons H2 and H3 in most cases. This has permitted assignment of substituents to one or other of these positions, an approach exemplified forderivatives of 5- and 6(7)-methoxy-1,4-naphthoquinone.