Tuesday, December 16, 2014

Otto N. Witt theory of Chromophore and Auxochrome

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

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