ABSORPTION AND EMISSION CENTERS. 25 



In condition I benzene has an aliphatic character, as in nitrobenzoic acid, 

 C H 4 (NO 2 )COOH. In this condition, having no double bonds, it does not 

 possess strong color properties. The second condition has an aromatic char- 

 acter and is exemplified in the phenols. Examples of the third condition are 

 found in aniline, p-phenylenediamine, naphthalene, or anthracene. Of the 

 three conditions, the second one is the best chromophore. According to KaulT- 

 mann, benzene vapor exists in the diagonal condition, and for that reason it 

 is not luminous when exposed to electric discharges of high frequency or to 

 the rays from radium. Auxochromes and chromophores cause the benzene to 

 become luminous, and for this and other reasons Kauffmann thinks that the 

 condition of the benzene grouping has been changed. 



The different changes in color may be due to one or more of three con- 

 ditions : 



(1) There may be no intramolecular changes of constitution, but the 

 whole change of color may be due to the change in the radicals. 



(2) There may be an intramolecular rearrangement. 



(3) There may be an association of the molecules or compounds formed 

 with the solvent. The above classification includes color changes that are not 

 explained by isomerism. 



In many cases it is practically impossible to decide between the different 

 possibilities. Auwers 1 and Tuck 1 ' give evidence to show that the sodium salt 

 of hydroxy azobenzene owes its color simply to the introduction of the sodium. 

 Baly and Schaefer, 3 Hantzsch, 4 Vey, Gorke, 5 and others, give some cases 

 coming under class 2. As an example, we may take dinitroethane : 



.NO, N0 2 N0 2 



CH,CH<: //O /y O 



'.( 



/ ran = N/ 



X N0 2 CH 3 C = Nf CH 3 C = N< 



X)Na x OH 



Pseudo acid, colorless. Sodium salt, yellow. Acid, yellow. 



o 2 n/ V>ch 3 "/N=< / N=o 



Nitrophenol ether, faintly yellow. Chromonitrophenol ether, deep red. 



Benzene derivative. Quinone derivative. 



A very full discussion of the "Umlagerung" theory is given by Ley. A 

 short discussion is also given of the theory of indicators, of polymerization, 

 and of metallic derivatives of organic compounds, especially of cases where the 

 metal is supposed to be present in the inner part of the molecular complex. 



^ieb. Ann., 360, 11 (1908). 



2 Journ. Chem. 80c, 91, 454 (1907). 



3 Ibid., 93, 1S0G (1908). 



4 Hantzsch: Ber. d. chem. Ges., 32, 575 (1899). Hantzsch and Veit: Ibid., 33, 626 

 (1900). Ley and Hantzsch: Ibid., 39, 3149 (1906). 



5 Hantzsch and Gorke: Ibid., 39, 1073 (1906). 



6 Jahrb. d. Rad. u. Elek., 6, 341, 381 (1909). 



