Otto N. Witt theory of Chromophore and Auxochrome

Otto N. Witt discovered the theory of Chromophore and Auxochrome in 1876. He explains-

Chromophore:

All organic compounds that contain certain unsaturated groups which are responsible for color are called chromophore.

Examples-  —N=O (Nitroso),  —NO2 (Nitro),   —N=N— (Azo),   >C=C< (Ethylenic),  >C=O (Keto)                                                                                         

Classification-

01. Independent chromophore – When a single chromophore is sufficient and does not need auxochrome to impart color to the compound, then it is called independent chromophore.

Examples- —N=O (Nitroso),  —NO2 (Nitro),   —N=N— (Azo) etc.

02. Dependent chromophore – When more than one chromophore is required to impart color in the chromogen, then it is called dependent chromophore.

Examples- >C=C< (Ethylenic),  >C=O (Keto) etc.

Auxochrome:

They are color helping or color intensifying groups. The auxochrome by itself does not produce color but it-

(i)            Generally deepen the color of a chromogen.

(ii)           Helps the chromogen to adhere to the textile fiber.