STRUCTURAL FORMULA 439 



Fischer and Stern, is in the second volume of Chemie des Pyrrols (Fischer and Orth 

 1940). Other reviews of chlorophyll chemistry have been given by Marchlewski 

 (1904), Tswett (1910), Treibs (1932), Linstead (1935, 1937), StoU and Wiedemann 

 (1938), and Steele (1937, 1943). 



The fundamental work of Willstatter and the systematic painstaking 

 research of Fischer rank among the outstanding contributions to the 

 organic chemistry of natural compounds, and have been recognized as 

 such by the award of the Nobel prize to Willstatter in 1915 and to 

 Fischer in 1930. 



The scope of the present book does not permit a detailed discussion 

 of the results obtained in the chemical studies of chlorophyll and its 

 derivatives; we must be content with a few fundamental facts and 

 hypotheses. Consequently, we shall refrain from quoting original papers, 

 and refer the reader to the above-mentioned comprehensive presentations 

 of the subject; a complete bibhography can be found in the book of 

 Fischer and Stern. 



2. Structural Formula 



We mentioned in chapter 15 that chlorophyll of the higher plants and 

 green algae consists of two components, chlorophyll a and chlorophyll h, 

 distinguished by their spectra, and separable because of their different 

 solubilities and adsorbabihties. Colored algae contain no chlorophyll b, 

 whose place seems to be taken by two related pigments, "chlorophyll c" 

 in brown algae and diatoms, and "chlorophyll d" in red algae (c/. Chap- 

 ter 15, page 406). The composition of these two pigments is as yet 

 unknown. That of the two original chlorophylls is as follows: 



chlorophyll a: C.5H.aN.Mg; mol. wt. §931 ^^^^.^^^^ ^ 450)_ 



chlorophyll b: C65H7o06N4Mg; mol. wt. 907 J 



This composition was established by Willstatter and coworkers; previ- 

 ously, iron and phosphorus had often been mentioned as probable 

 components of chlorophyll. Willstatter found that the chlorophylls are 

 esters of two dibasic acids which he called chlorophyllins: 



chlorophylhn a: CaaHaoONiMg (C00H)2 

 chlorophylUn b: C32H2802N4Mg (C00H)2. 



The esterifying alcohols are methanol (CH3OH) and p/i?/ioZ (C2oH3aOH). 

 The latter is a long-chain alcohol with one double bond; its structure 

 (Formula 16.1) has been confirmed by synthesis by F. G. Fischer and 

 Lowenberg (1929). 



The arrangement of methyl groups in phytol shows a relation to isoprene. The 

 chain length (C20) is one-half that of the carotenoids; a genetic relationship of phytol 

 to these compounds has often been postulated. However, in contrast to the carotenoids, 



