CHLOROPHYLLS a AND h 609 



chlorophylls, which they called a' and b' and interpreted as tautomers of 

 chlorophylls a and b. The forms A, B and C have different double bond ar- 

 rangements in the nonhydrogenated pyrrole nuclei, but the same hydro- 

 genated nucleus IV. Since the red absorption band is somehow associated 

 with the hydrogenation of this nucleus (cf. page 621), modifications A, B 

 and C may have identical red bands. They could, however, differ in the 

 positions or shapes of the blue-violet bands, associated with the conjugated 

 porphin system as a whole. 



Erdman and Corwin (1946) noted the spectroscopic similarity of etio- 

 porphyrin and A'"-methyl etioporphyrin, and deduced from this that the 

 two "central" H-atoms in the porphin system must be fixed at definite 

 nitrogen atoms for » 10"* sec. This supports the hypothesis that struc- 

 tures such as those represented by the three formulas in figure 21.2 are 

 tautomeric rather than mesomeric. 



We have used so far only data obtained with ethyl ether as solvent, 

 since they alone offered the possibility of comparison between the results 

 of several observers. Determinations of extinction curves of chlorophyll 

 in solvents other than ether are Usted in Table 21.11. 



Table 21.11 

 Chlorophyll Extinction Measurements in Various Solvents 



Solvent Reference 



Methanol, Rabinovvitch and Weiss (1937) (ethyl chlorophyl- 



Ude); Harris and Zscheile (1943); Mc Brady and 



Livingston (1948, 1949) 

 Ethanol Meyer (1939); Sprecher von Bernegg, Heierle and 



Almasy (1935) 



Butanol (71- and iso-) Harris and Zscheile ( 1943)" 



Octanol Harris and Zscheile (1943)" 



l-Propyl ether Harris and Zscheile (1943)" 



Dioxane Harris and Zscheile (1943)" 



Benzene .... Winterstein and Stein (1933); Hausser {cf. Fischer 



and Stern, 1940; Harris and Zscheile (1943) 



Cyclohexane Harris and Zscheile (1943) 



Acetone Mackinney (1940); Harris and Zscheile (1943) 



Carbon tetrachloride Harris and Zscheile (1943)" 



Methyl oleate Harris and Zscheile (1943)" 



Olive oil Harris and Zscheile (1943)" 



" Several of the curves of Harris and Zscheile (1943) are reproduced in figure 21.26. 



The absorption spectra of the two chlorophylls in the ultraviolet are 

 shown in figure 21.3. The absorption remains considerable all the way 

 down to 200 m/u; the most prominent band is a double band of chlorophyll 

 b at 310 and 335 mju. In the spectrmn of chlorophyll a, distinct maxima 



