CONSTITUENTS OF THE BIOSPHERE 31 



(a) Lower Terpenes 

 These result from the condensation of two (monoterpenes), three 

 (sesquiterpenes), four (diterpenes), six (triterpenes), or eight (tetraterpenes) 

 isoprene residues. The lower terpenes are widely distributed in the essen- 

 tial oils of many plants. Phytol, an unsaturated alcohol present in the 

 chlorophyll molecule, is a diterpene derivative. 



CH3— CH— (CH2) 3— CH— (CH2) 3— CH— (CH., ) 3— C=CH— CH2OH 



CH3 CH3 CH3 CH3 



Phytol 



(6) Carotenoids 

 1. Definition 



One of the groups of natural isoprene derivatives is that of the caroten- 

 oids — aliphatic or alicyclic pigments whose colours range from yellow to 

 red. According to Karrer, they are derivatives of several isoprene units 

 (often eight) joined together in a manner such that the two methyl groups 

 at the centre of the molecule are 1 : 6 to each other, whilst the remaining 

 lateral methyl groups are in the 1 : 5 positions. 



— C=CH-CH=CH-C=CH— CH=CH-CH=C-CH-CH-CH=C- 

 I I 



CH3 CH3 



I 



I 



©- <p 



CH, CH, 



I 



(j> <D 



O ' -d) 



The chain of conjugated double bonds forms the chromophore system 

 of the carotenoid pigments. 



2. Classification 



There are two classes of natural carotenoids : the carotenoids proper, 

 having a C-40 chain (8 isoprene residues), and the carotenoids possessing 

 less than 40 carbon atoms. The natural carotenoids can be considered as 

 related to lycopene (C40H56), the red pigment of the tomato. 



CHa CH3 H.C CH, 



\ / \ / 



Ci CH, CH» CH, CH, rC 



// (< 1 \ I 1 I 7' 6' \ 



2CH CHCHzrCHC=CHCH=CHC=CHCH=CHCH=CCH = CHCH=iCCH=CHCH 2'CH 



! !| 8 9 10 II 12 13 14 15 15' 14' 13' 12' 11' 10' 9'8' II I 



3.CH2 C C 3'CH, 



\ /S\ /S'\ / 



\ / CH, HaC CHc 



CHj Lycopene 4' 



4 



