296 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The configuration of lanceol (XV), a primary sesquiterpene alcohol present in oil of Santalum lanceolatum, remained doubtful for a long time, but recently a tentative formula, based upon •-bisabolene, has been as- signed to it (24, 55, 101,144). I•CH•OH Lanceol (xv) Metrosiderene (XVI), a hydrocarbon present in oils of Metrosideros umbellata and Dacrydium biforme, is now considered a sesquiterpene of the cadinene type, but the position of the double bonds has not yet been clearly explained (42). Metrosiderene (xvi) Carotol (XVII), a bicyclic sesquiterpene alcohol and chief component of carrot seed oil, has also been found to belong to the cadinene type (144). Carotol (XVII) Zingiberene (XVIII), which is present in ginger root oil, has been re- examined (108) and its absolute configuration now appears clear (9, 54). I Zingiberene (XVlii)

RECENT DEVELOPMENTS IN ESSENTIAL OILS 297 Sesquiterpenes of the Eudesmol Type Some of the most important sesquiterpenes and their oxygen derivatives belong to this group (santalene, santalol, alantolactone, etc.) their structures have been known for some time. Newly investigated are artemisin (8-hydroxysantonin) (XIX) isolated from the seed of Atrtemisia maritima (144), and carissone (XX), a ketonic sesquiterpene present in the roots of Carissa lanceolata R. Brown (19). ¾7,o O:C 0 Artemisin Carissone (XlX) (XX) A great amount of work has been carried out on the naturally occurring a- and 3-santonins (XXI), lactonic sesquiterpenes of the eudesmol type their absolute configurations are now well established (1, 2, 3, 4, 12, 36, 37, 39, 41, 43, 45, 65, 66, 91, 92, 144, 184). •-Santonin (XXII), too, has been investigated extensively (31, 38, 40, 45, 46, 144). o I I O--C--O O:C--O and •-Santonin •k-Santonin (XXI) (XXlI) Measuring the differences in molecular rotation, and using techniques of oxidative degradation in conjunction with rotational analysis, it was possible to explore the stereochemistry of a- and 3-eudesmol, a-selinene and a- and •-cyperone (11, 85, 86, 96, 97, 138, 140). The structure of elemol (XXIII), an "irregularly built" sesquiterpene alcohol related to eudesmol, remains uncertain, despite the recent work of •orm, Herout and other collaborators (166, 167) there is still doubt re- garding the position of the double bonds and of the OH group. Elemol (XXIII) (?)