COLOR AND STEUCTURE IK ORGANIC 

 COMPOUNDS* 



BY W. L. JEFFRIES 



The very large number of organic componnds whicli are 

 colored and the important place the dye stuffs occupy in modern 

 industry have naturally caused chemists to seek some explana- 

 tion of the color in compounds and just what relation the color 

 ■bears to the structure. 



'In 1876 O. N. Witt offered the theory that color in organic 



compounds is due to the presence of certain unsaturated groups 



which are termed chromophores. The most important of these 



groups are the following: 



O 



// 

 C=C, C=0, C=S, C=N, N=N, Ni=0, N . The ortho- and para- 





 quoinoid radicals, 



ortho-quinoid para-quinoid 



which may be regarded as a compact arrangement of the 0=C 

 group, were later added to the list. 



A carbon complex containing such a group or chromophore is 

 termed a chromogen. The chromogen may or may not be col- 

 ored. If colorless it is necessary to introduce some salt-forming 

 group such as NHg or OH. A group of this character is termed 

 an auxochrome. For example, benzophenone, CeHg.CO.CeHg, al- 

 though colorless is a chromogen since it contains the Ct=0 

 group. On the introduction of the auxochrome, NII2, to form 

 aminobenzophenone, the compound becomes yellow. Similarly 

 the nitro group is the chromophore of the chromogen nitroben- 

 zene which forms the coloring matter of nitraniline. 



Color, depending on the chromophore, is intensified by its 



* A report road at the January meeting of the N. C. Section of the American 

 Chemical Society. 81 



