TERPENOIDS AND STEROIDS 



125 



The bicyclic monoterpenoids are divided into seven classes according to their carbon 

 skeletons. These are as follows: * 



Thujane 

 (Sabinane) 



Fenchane 



Camphane (Bornane) 



iso -Camphane 



jso -Bornylane 



These forms are easily visualized as derived from the monocyclic compounds by 

 additional ring closures. The best known of this group (and possibly of all the terpenoids) 

 is a-pinene, the chief component of turpentine. The structure of it and of a few of the 

 other more important bicyclic monoterpenoids are given in Table 4. 



Although usually classed as aromatic compounds, some constituents of essential 

 oils are clearly related to the terpenoids. For example p-cymene and thymol found in 

 oil of thyme are respectively: 



and 



*It has been proposed (6) to name the last three structures as, respectively, 2, 2, 3-trimethylnorbornane, 1 , 3, 3-trimethylnorbornane, 

 and 2,7,7-trimethylnorbomane. 



