6 I. GENERAL CHARACTERISTICS AND CLASSIFICATION 



(6) Carotenoids. Most important are the three carotene isomers a, /3, 

 and 7, all of which have an identical empirical formula, C40H56. Lycopene 

 also falls in this category, but the ionone ring is niptured in the latter com- 

 pound. 



(c) Squalene (C30H50). This hydrocarbon related to the carotenoids is 

 found in shark-liver oil. 



d. Vitamins D. These compounds are found in the non-saponifiable 

 extract, but differ from the sterols principally because the steroid nucleus 

 is ruptured between carbons 9 and 10. These are present in fish-liver oils 

 as esters (before saponification) or may be synthesized in other oils which 

 contain 7-dehydrocholesterol or ergosterol when these are subjected to ir- 

 radiation with ultraviolet light. 



e. Vitamins E. The chroman derivatives, a, /8, 7, and 8 tocopherols, 

 are compounds found in natural oils (chiefly vegetable) of varying vita- 

 min E potency. These occur in high concentration in corn, cottonseed, 

 and soybean oil. 



f. Vitamins K. These vitamins are derivativ'es of 1,4-naphthoquinone 

 and contain long hydrocarbon side chains. Their occurrence in fats and 

 oils is extremelv limited. 



