Periodate oxidation studies, nuclear magnetic resonance spectra of derivatives, and X-ray crystallographic data have shown that plicatic acid, the major component of the heartwood extractive of western red cedar (ThujaplicataDonn), is 2,3,6-trihydroxy-7-methoxy-2-hydroxymethyl-4-(3′,4′-dihydroxy-5′-methoxyphenyl)-tetralin-3-carboxylic acid. The asymmetric configuration by X-ray data is 2R,3S,4R or its enantiomer, by Cahn–Ingold nomenclature.