Basic auxochromes. Auxochrome vs chromophore. Auxochrome is a Greek word arising from two word roots; ‘auxo’ meaning “to increase” and. This lesson explains the parts of a molecule responsible for color: chromophores and auxochromes. Chromophores and auxochromes are. In , Witt proposed that dye molecules contain two groups; the chromophore and the auxochrome. The chromophore is a group of atoms which control the.
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They themselves fail to produce the colour; but when present along with the chromophores in an organic compound intensifies the colour of the chromogen. 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.
Difference between auxochrome and chromophore
A feature of these auxochromes is the presence of at least one lone pair of electrons which can be viewed as extending the conjugated system by resonance. It increases the color of any organic compound. Similar behavior is seen in azobenzene which has a red color, but p -hydroxyazobenzene is dark red in color.
The auxochdome of an auxochrome in the chromogen molecule is essential to make a dye.
However, if an auxochrome is present auxocyrome the meta position to the chromophore, it does not affect the color. An auxochrome is known as a compound that produces a bathochromic shiftalso known as red shift because it increases the wavelength of absorption, therefore moving closer to infrared light.
An auxochrome helps a dye to bind to the object that is to be colored. Electrolytic dissociation of the auxochrome group helps in binding and it is due to this reason a basic substance takes an acidic dye.
A molecule exhibits colour because it absorbs colours only of certain frequencies and reflects or transmits others. They are capable of absorbing and emitting light of various frequencies. Light waves with frequency very close to their natural frequency are absorbed readily. This phenomenon, known as resonancemeans that the molecule can absorb radiation of a particular frequency which is same as the frequency of electron movement within the molecule.
The chromophore is the part of the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum and hence absorbs some particular colours from visible light. Hence the molecule appears coloured.
When auxochromes are attached to the molecule, the natural frequency of the chromophore gets changed and thus the colour gets modified. Different auxochromes produce different effects in the chromophore which in turn causes absorption of light from other parts of the spectrum.
Normally, auxochromes which intensify the colour are chosen.
chemistry of dyes
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