An allelopathic aromatic mixture found in the leaves, roots, husks, and bark of flowers in Juglandaceae household, specially the black colored walnut, used as a colouring representative.
A yellow crystalline substance (C10H6O3) resembling quinone, obtained from green shucks regarding the walnut (Juglans regia); -- called also nucin. Chemically, it's 5-hydroxy-1,4-naphthalenedione.
A yellowish- or brownish-red element, HOC10H5O2. prepared by the oxidation of a-hydrojuglone from the green components of the walnut-tree; a-hydroxynaphthoquinone, nucin, or regianin. It crystallizes in needles or prisms and melts at 151–154° C.