Question

Write the chromogen, chromophore and auxochrome present in para hydroxy azo benzene.

Answer 1

Hint: The term chromogen is applied to a colourless chemical compound that can be converted by chemical reaction into a compound which can be described as coloured and chromophore is the portion of a molecule's structure which absorbs visible light photons, causing the molecule to have color and An auxochrome is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light.

Complete answer:
The structure of para hydroxy azobenzene is:
$OH - {C_6}{H_4} - N = N - {C_6}{H_5}$
A chromogen is a substance capable of conversion into a pigment or dye Or any substance that can become a pigment or coloring matter, a substance in organic fluids that forms colored compounds when oxidized, or a compound, not itself a dye, that can become a dye.
In the structure of para hydroxy azobenzene the chromogen is represented as:
${C_6}{H_5} - N = N - {C_6}{H_5}$
The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.
In the structure of para hydroxy azobenzene the chromophore is represented as:$ - N = N - $
An auxochrome is a functional group of atoms with one or more lone pairs of electrons when attached to a chromophore, alters both the wavelength and intensity of absorption. If these groups are in direct conjugation with the $pi - $ system of the chromophore, they may increase the wavelength at which the light is absorbed and as a result intensify the absorption.
In the structure of para hydroxy azobenzene the auxochrome is represented as:$ - OH$.
So, the correct answer is $B)$ Charge on the electron.

Note:
The presence of an auxochrome in the chromogen molecule is essential to make a dye. However, if an auxochrome is present in the Meta position to the chromophore, it does not affect the color. An auxochrome is known as a compound that produces a bathochromic shift, also known as red shift because it increases the wavelength of absorption, therefore moving closer to infrared light.