1512 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



substituted for the complex formation and decomposition ; the assumption 

 of a back reaction reversing oxidation is needed in this case to make the 

 over-all yield dependent on the concentration of phenylhydrazine, as repre- 

 sented in equation (35.21). 



Livingston and Pariser extrapolated the observed quantum yields to 

 [PH2] = CO by means of the following equation : 



(35.22) 



'^(PHjlcD 



^ V '^ hlPH,]) 



using for the ratio ki/k/ an empirically estimated value, 10^ liters/mole. 

 This extrapolation changed the values of 7 significantly only for the lowest 

 phenylhydrazine concentrations used — [PH2] from 0.02 to 0.05 mole/liter. 



i>« 



1 / [mr"] 



Fig. 35.4. Quantum efficiency of chlorophyll-sensitized reaction of methyl red 

 and phenylhydrazine in relation to concentration of methyl red in form II (after 

 Livingston and Pariser 19-18). 



The values of I/7 for [PHo] = 0° were plotted against 1/[MR"] 

 and, in accordance with equation (35.22), an approximately straight line 

 was obtained (although the individual values scattered considerably). 

 From the slope and the intercept of this straight line (fig. 35.4), the follow- 

 ing ratios could be derived: 



(35.23) 



h/(kf + kt) = 0.92 



h/k = 5.0 X 10< liters/mole 



The first value means 8% fluorescence and 92% tautomerization (a plan 

 sible result as far as the yield of fluorescence is concerned), and thus an 



