α-Farnesene in the Natural Coating of Apples

EARLIER1, we reported the presence in the natural coating of ‘Granny Smith’ apples of a hydrocarbon which we identified as the naturally occurring sesquiterpene β-farnesene (I)2–4. Identification was based on a comparison of its infra-red spectrum with that published for β-farnesene isolated from natural sources4, together with the unequivocal identification of its fully hydrogenated product as farnesane (2,6,10-trimethyldodecane)2,3by comparison of its infra-red and mass spectra and gas chromatographic retention times with those of a pure authentic specimen. Additional evidence was, however, deemed necessary, and direct comparison with pure β-farnesene has now established that this identification was incorrect and that the farnesene present in apple coating is not the β- but the α-isomer (II), which has hitherto not been reported as naturally occurring or prepared in a pure state.