PROPERTIES OF THE CAROTENOIDS 



629 



m 



.<"--^-^^>' 



'^ 



Fig. 15. Skeleton models of the 20 possible stereoisomers of 

 /3-Carotene, according to Zechmeister.''" 



e. Methods of Producing Stereoisomeric Changes. There are a num- 

 ber of methods which can be employed to bring about stereochemical 

 changes in the aW-trans isomers. Under such treatment, an equilibrium 

 mixture of a number of different isomers results, the aW-trans form usually 

 being present in the preponderant amount. If one uses as the starting 

 material one of the cis isomers instead of the all-frans compound, a similar 



