Important terms

 

Chromophore: A covalently unsaturated group responsible for electronic absorptions or any group of atoms that absorbs light whether or not a color is thereby produced.. For example C=C, C=O, NO₂ etc. A compound containing chromophore is called chromogen. There are two types of chromophore

1. Independent chromophore: Single chromophore is sufficient to import color to the compound eg. Azo group .

2. Dependent chromophore: When more then one chromophore is required to produce color. eg acetone having one ketone group is colorless where as diacetyl having two ketone group is yellow.

Auxochrome: A saturated group with nonbonded electrons which, when attached to a chromophore, alters both the wavelength and the intensity of the absorption or A group which extends the conjugation of a chromophore by sharing of nonbonding electrons e.g. –OH, -NH₂ –Cl etc..

 

Bathochromic group: The group which deepens the colour of chromophore is called bathochromic group. e.g. primary, secondary and tertiary amino groups.

Bathochromic shift: The shift of absorption to a longer wavelength due to substitution or solvent effect is termed as bathochromic shift. This is also known as red shift.

Hypsochromic shift: The shift of absorption to a shorter wavelength is termed as hypsochromic shift. This is also known as blue shift.

Hyperchromic shift: An increase in absorption intensity

Hypochromic shift: An decrease in absorption intensity