Absorption and intensity shift

educational purpose

1. PRESENTATION ON ABSORPTION AND INTENSITY SHIFT

2. WELCOME TO MY PRESENTATION

3. PRESENTED BY – Khondaker Afrina Hoque ID -1114015 Reg- 900048 Session-2011-12

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. HYPOCHROMIC SHIFT 4 Auxochromic substituents may have any of 4 effects on chromophore

6. - Absorption shifted toward longer wave length. -Due to the change of solvent and auxochrome. Example:

7. 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.

8. 3: bathochromic shift also result s from the increase of conjugated system.

9. -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 :

10. 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.

11. 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

12. 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

13. THAT’S ALL AND THANKS TO ALL