608 ABSORPTION SPECTRA OF PIGMENTS 7.V VITRO CHAP. 21 



H2C=CH CH3* HT rn 



.C, ,C C i H I 



C N N C V ., \. _/ 



H,c-c< El I ir |c-CH, „^ o< m \ \ m\ 



/\ \ H \ c c ^c' 



H^i I,,".: 



CH2 HC C. 



H I lio 9. u 1 . 



CH2 HC C. ^ 1. .iio 9 



^^^y'°'^ I I \ (Phytol) I ' T X 



H39C20OOC-CH2 COOCH H r mr L i 



H39C20OOC — CH2 COOCH 



A B 



H2C=CH CHj* 



' H I 



H3C-C(r^ I J C jj >C-C2H, 



C N N C 



HC S Mg fl CH 



C N N C 



3 



" \/ ^J< V 



CHg HC C 



(Phytol) I I \ 



H39C20OOC— CHj COOCH 



Fig. 21.2. Chlorophyll a structure according to Hans Fischer. A, B and C are three 

 isomeric or tautomeric (or mesomeric) structures, distinguished by the routing of the 

 all-roimd conjugated ring system (heavy line) and the positions of the "semi-isolated" 

 double bond and of the Mg— N bonds (all of which depend on this routing). The 

 asterisk designates the position of a carbonyl group in chlorophyll h. A, semi-isolated 

 double bond in nucleus III ; Mg bound to nuclei I and II. B, semi-isolated double bond 

 in nucleus II; Mg bound to nuclei I and III. C, semi-isolated double bond in nucleus 

 I; Mg bound to nuclei II and III. 



We recall that the three structures of chlorophyll, A, B and C, described 

 in chapter 16, Vol. I, (c/. fig. 21.2), were characterized there as probably 

 tautomeric rather than mesomeric. We also recall that Strain and Mann- 

 ing found {cf. page 403) in the chromatograms of leaf extracts, two new 



