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bicyclic terpenes, C10H16; colorless liquids with the odor of pine cones. Freely soluble in nonpolar organic solvents, insoluble in water, and readily oxidizable upon exposure to air, especially in light. Of the three known α-, β-, and δ-isomers, only α-pinene and β-pinene, or nopinene, are widespread in nature (respective boiling points, 155.9° and 166°C; densities, 0.858 and 0.871 g/cm3 at 20°C). Both α- and β-pinenes occur in various turpentines, from which they are extracted by rectification, and in many essential oils.
Pinenes are extremely reactive. Upon heating to temperatures above 300°C, α -pinene isomerizes to allo-ocimene, and β-pinene to myrcene; pinenes polymerize readily under the action of acids. Pinenes are used as solvents for varnishes and paints and as raw material in the manufacture of camphor, terpineol, terpin hydrate, insecticides, and odoriferous substances.