12 



THE ABSORPTION SPECTRA OF SOLUTIONS. 



The nitro group N 



\ or 



-N< 



,0 

 ^0 



is a very weak chromophore. 



The aliphatic nitro compounds, CH 3 N0 2 , C 2 H 5 N02, etc., are colorless. When 

 combined with other chromophores, colored compounds, such as nitroben- 

 zene or nitronaphthalene, can be obtained. Stobbe 1 has investigated the 

 influence of the nitro group on the fulgides. In solution the p-nitrophenyl- 

 fulgide has a deep red color. The ortho and meta compounds are much less 

 deeply colored. 



Hantzsch 2 and Raschig 3 have shown that the = N =0 group acts as a 

 chromophore in the sulphonate, O = N = (S0 3 K) 2 , which is violet in solution 

 and orange in the solid state. The thiocarbonyl group, = C = S, is a rather 

 strong chromophore. Examples are the blue compounds thioacetophenone, 

 C 6 H 5 CS CH ;i , and thiobenzophenone, C 6 H 5 CS C 6 H 5 . For a fuller 

 account of the color properties of various compounds, the reader is referred 

 to Ley's paper, 4 from which the data here recorded have been largely taken. 



There has been a great deal of discussion whether quinone has the for- 

 mula I or II: 



= 



-0 







Willstatter and F. Miiller 5 have found that o-benzoquinone can exist in 

 two forms, I and II, the former being colorless and the latter red: 



/ 



\ 



// 



-0 

 -0 











/ 



II. 



This fact may possibly explain several outstanding difficulties among 

 quinone derivatives. It would be expected that the substitution of an (NR) 

 group for oxygen in a quinone would give a deeply colored substance. As a 

 matter of fact, quinonediphenylimide, 



C 6 H 6 N=< 



NCJL 



1 Ber. d. chem. Ges.. 38, 4082 (1905). 



2 Ibid., 28,2744(1895). 



8 Dammer: Handb. d. anorg. Chem. 



4 Jahrb. d. Rad. u. Elek.. 6, 274-381 (1909). 



5 Ber. d. chem. Ges., 41, 2580 (1908). 



