82 JouEisrAL OF THE MiTCHELL SociETY \_January 



reduplication. For examjDle hjdrocaAons of the ethylene series, 



diphenyl- and tetraphenjlethylene are colorless but diphenyl- 



bexatriene, CeH^.CH :CH.CH iCH.CHiCH.CeHg, is yellow. 



Absorption of color in the visible spectrum and the production 



of color seems to be promoted by the compact arrangement of 



double linkages in the ring structure. An example of this is the 



series of colored hydrocar'bons discovered by Thiele and known 



as fulvenes. 



CH=CH CH=:CH CHs 



I >C=CH2 I >C=0< 



CH=CH CH=CH C0H5 



Fulvene — yellow liquid Methylphenylfulvene — orange liquid 



Being isomeric with fulvene and containing the same number 

 of double linkages, it might be expected that benzene would be 

 colored. That it is not may be accounted for by the difference 

 of the grouping of the double bonds which cause the absorption 

 bands to shift within the ultra violet region of the spectrum. It 



— C 



seems certain that the > C = group is an. important factor 



in color production. The influence of ring structure in deepen- 

 ing color is shown in flourenone, 



CCH4-CH4 



\ / 

 C 



which is red while benzophenone is colorless. Reduction or 

 replacement by chlorine and sometimes hydration of the CO 

 group destroys color. 



Although the color effect of the 0^=0 group is not apparent 

 in the simple aldehydes or ketones or even in compounds where 

 the C^O groups are separated such as acetylacetone, CH3.CO.- 

 CH2.CO.CH3, a continuity of these groups does produce color. 

 To illustrate, diacetyl, CH3.CO.CO.CII3, is yellow and the an- 

 hydrous triketone CH3.CO.CO.CO.CH3, is orange. The color 

 appears to deepen with the increase in the number of 0^=0' 

 groups. 



The C:S group appears to have greater effect as a chromo- 

 phore than the C:0 group as instanced by comparing tetra- 

 methyldiaminothiobenzophenone, OS[C6H4N(CH3)2]2, which 

 is yellow while the corresponding ketone is colorless. 



