educational purpose

1. PRESENTATION ON
ABSORPTION AND
INTENSITY SHIFT

4. Chromophore: A covalently unsaturated group
responsible for electronic absorption. or Any group of
atoms that absorbs light whether or not a color is
thereby produced
eg: NO2, N=O, C=O, C=N, C=C, C=S etc
Auxochrome: A saturated group with non-bonding
electron when attached to chromophore alters both
wave lengths as well as intensity of absorption
e.g. OH, NH2, NHR etc
Concept of chromophore & auxochrome

5. 1
• BATHOCHROMIC SHIFT
2
• HYPSOCHROMIC SHIFT
3
• HYPERCHROMIC SHIFT
• HYPOCHROMIC SHIFT
4
Auxochromic substituents may have any of 4 effects on
chromophore

7. -Absorption shifted toward longer
wave length.
-Due to the change of solvent and
auxochrome.
Example:
BATHOCHROMIC SHIFT ( RED SHIFT1

8. 2: an auxochrome group like –OH , OCH3 , -CH3 show
bathochromic shift
1:n-∏* transition for carbonyl compound experiences
the bathochromic shift when the polarity of the
solvent decreased.

9. 3: bathochromic shift also result s from the increase of
conjugated system.

10. -Shift toward shorter wave length .
-Due to the change of solvent towards higher
polarity or removal of conjugation or due to
the effect of auxochrome.
-eg:
Hypsochromic shift ( blue shift)2

12.  Substitution on carbonyl group by an auxochrome
with a lone pair of electrons, such as- NR2 ,- NHR,
OH ,-OR, -X as in amide ,acid ,acid chlorides, esters
gives a pronounced hypsochromic effect on n-∏*
transition.

13. -Shift due to increase in intensity .
-Due to introduction of auxochrome.
-Alkyl substitution produces hyperchromic effect
-Example: pyridine -257nm and Emax is 2750;
- 2-methy pyridine – 262 nm and Emax – 3560
HYPERCHROMIC SHIFT3

14. Inverse of hyperchromic shift
-I.e. decrease of intensity
--introduction of any group to the compound s which
going to alter the molecular pattern of the compound
results in hypochromic shift.
-- ex: biphinyl absorption is 250 nm and Emax -19000
--where 2- methyl biphinyl has an absorption of
257nm and E max is 1o250
HYPOCHROMIC SHIFT)4

15. THAT’S ALL AND
THANKS TO ALL