Pigments of Elsinoe species. Part IV. Confirmatory evidence for the structure of elsinochrome A and its ethers from studies of nuclear magnetic resonance (solvent and overhauser effects) and electron spin resonance

Abstract

The structures assigned to elsinochrome A and its two isomeric dimethyl ethers have been confirmed by the use of special techniques of magnetic resonance spectroscopy. Nuclear Overhauser effects involving methoxy-groups and adjacent aromatic protons have been observed; signals from such methoxy-groups show larger half-line-widths in the unperturbed n.m.r. spectra than do those of groups without free ortho-positions. These observations should be helpful in structure elucidations.