628 VI. CAROTENOIDS AND RELATED COMPOUNDS 



The structural formulas for all-irans a-, /3-, and 7-carotenes as well as 

 for all-frons-lycopene are given here, showing the stereochemically effective 

 double bonds, which are numbered by underlined figures. 



A 



"^? 9'^"^'^ CHj CH3 CHj 



i i h h h h h i^h i^h 1^ 

 IhIhIhhhhh|| 



^"' ^"' ^"^ (H.OaC CHj 



c 



Hz 



All-<;-a/iS-/3-carotene 



/ \ 



HjC C(CH3)2 



ICn3 CHi CHt 



I H H H H H I H I H I 



HjC CCCCCCCCCCC, 



C^ C C^ C C^ C^ C^ C C^ C C CH 



I H I H 1 H H H H I I 



^"' ^"' ^^' (H3C),C ,CH, 



Ha 

 All-trans-a-carotene 

 H, 



"^? ?'^"'^^ CH, CH3 CH3 



I iHHHHHlHlHlH, 



|H I H I HHHHHHH^H 



CH3 CHj CH, 



All-irans-y-carotene 



CM, CH3 CH3 



HH_HHHHHH|H|H|H2 



H, iHlHlHHHHHHHjH 



CH3 CH3 CHj 



All-^ra«5-lycopeiie 



Skeleton models of the 20 possible stereoisomers of /3-carotene are in- 

 cluded in Figure 15. In addition to alI-/ran.s-(3-carotene (1), these include 

 the three mono-cis-/3-carotenes, the six di-cis-jS-carotenes, the six tri-cis-^- 

 carotenes, the three tetra-cfs-j8-carotenes, and the all-cts-/3-carotene. 



The structural formulas for all-/rans-lycopene and for several stereo- 

 chemical isomers are included in Figure 16. This method of presentation 

 attempts to represent the relative space occupied by the hydrogen atoms 

 and the methyl groups, and affords the most accurate picture of molecular 

 shape w^hich can be given on a two-dimensional drawing. 



