CAROTENOIDS 



hydroxyl group in each ring, « * they must occupy positions 3- or 4- 

 and 3'- or 4'-. 



It seems certain that the position of the group attached to the 

 a-ionone ring is 3'- because an hydroxyl group in position 4'- would 

 have enolic properties ; the attachment in the other ring is accepted 

 as being as position 3- only by an ** analogy of symmetry " in a molecule 

 which is asymmetrical. In many eyes, however, the tentatively sug- 

 gested position (3-) in the p-ionone ring has now become an accepted 

 fact and it is therefore important to emphasize its equivocal position. 

 Further, recent work by Goodwin and Taha^' indicates that position 

 4 might well be the correct one. 



Me 

 Me—/-. 



Lutein (Xanthophyll) 



Table 2. — Leaf Xanthophylk 

 (after Strain unless otherwise stated) ^ * 



The reference numbers are to the end of Chapter 2. 

 * These data are for pigments isolated from flowers. 

 t Not observed by Strain. 



14 



