630 



VI. CAROTENOIDS AND RELATED COMPOUNDS 



equilibrium mixture obtains after treatment, since the isomerization is 

 reversible. When any stereoisomer is subjected to the treatment by 

 which it was produced, only members of the same stereochemical set can 

 appear. 



f^ (wi) riT) r»\ (») r»^ (^ r»i cHj fyi CH, Yy\ cHj i\^ 



0".. 



.^- 



U L^l CH, tHT CH, Ih; (^ ^ ^ ^ ^ ^ (J^^ 



Fig. 16. Suggested stereochemical structures of some members of the 

 lycopene set; these include all-/rans-lycopene (I ), neolycopene A (II ), d-cis- 

 lycopene (III), prolycopene (IV), and all-m-lycopene (V).^" 



The all-trans carotenoids are stable as long as they are in the crystalline 

 state and are not subjected to heating or over-exposed to oxidation. How- 

 ever, as soon as they are dissolved, they become readily susceptible to such 

 catalysts as iodine and acid, as well as to photo-isomerization, or to ther- 

 mal isomerization in solution. 



