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