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[[file:beta-thujone.png|thumb|200px|right|Thujone]]
'''Thujone''' (C<sub><font size="-2">10</font></sub>H<sub><font size="-2">16</font></sub>O) is a chemical compound. It is a colourless liquid with a distinctive menthol odour, it is a ketone, a monoterpene, and is found in two stereoisomeric forms - (+)-3-thujone or &alpha;-thujone and (-)-3-thujone or &beta;-thujone. It boils at 201&deg;C, is insoluble in water although it is readily soluble in [[ethanol]] or [[diethyl ether]].

It is found in certain plants such as ''arborvitae'' (genus ''Thuja'', whence the derivation of the name), Nootka Cypress, some [[juniper]]s, mugwort, sage, and wormwood, usually as a mix of isomers in a 1:2 ratio. Its name is sometimes given structurally as bicyclo (3.1.0) hexan-3-one, 4-methyl-1-(1-methylethyl)-,(1S-(1-, 4-, 5-&alpha;))-(9CI), other names used include isothujone and thujanone. It is used as a flavouring agent in certain foods and is a compound in a number of other food additives.

It is best known as a component of the drink [[absinthe]], as it is a natural oil of [[wormwood]] (''[[Artemisia absinthium]]''). Although the compound is credited with hallucinogenic properties this is not certain; it is structurally close to Tetrahydrocannabinol (THC) and is certainly toxic but each isomer has distinct differences.