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Chemistry

Chemistry. GOC–3. Session Objectives. Session Objectives. Structural isomerism: chain, positional, functional, ring-chain, isomerism, metamerism , tautomerism Homologous series Stereoisomerism: conformational, optical and geometrical isomerism. Isomerism. Isomerism. Next slide.

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Chemistry

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  1. Chemistry

  2. GOC–3

  3. Session Objectives

  4. Session Objectives • Structural isomerism: chain, positional, functional, ring-chain, isomerism, metamerism , tautomerism Homologous series • Stereoisomerism: conformational, optical and geometrical isomerism

  5. Isomerism Isomerism Next slide Structrual Chain Functional Positional Ring Chain Metamerism Tautomerism

  6. Isomerism Isomerism Stereoisomerism Previous slide Conformational Configurational Optical Geometrical

  7. Structural Isomerism

  8. Structural Isomerism Functional Isomerism Same molecular formulae but differ in the functional groups. CH3 CH2 OHCH3OCH3 Positional Isomerism same molecular formulae but differ in the position of the same functional group.

  9. Structural Isomerism Disubstituted benzene has three positional isomers. e.g.

  10. Structural Isomerism Metamerism same molecular formula but the distribution of alkyl groups on either side of the functional group is dissimilar. Occurs in amines, ketones, ethers and esters.

  11. Structural Isomerism Ring chain isomerism Due to the difference in linkage of carbon atoms in the form of ring or open chain structure, i.e. C3H6

  12. Structural Isomerism Tautomerism Existing of single compound in two readily interconvertible structures called as tautomers which appears in acid catalysed or base catalysed conditions. Tautomerism keto-enol nitro-aci nitrite-nitro

  13. Structural Isomerism keto-enol isomerism Contains a keto and an enol group. For example, in the presence of an acidic or basic catalyst a rapid equilibrium is established between an aldehyde or ketone and its isomeric (tautomeric) forms.

  14. Structural Isomerism Shows keto-enol tautomerism Does not show keto enol tautomerism

  15. Structural Isomerism Nitro-aci tautomerism nitrite-nitro tautomerism

  16. Difference between resonance and keto-enol tautomerism • Keto-enol tautomerism • Change in the position of an atom, generally a H–atom. • Exist in solution as they are different compounds. • Exist in dynamic equilibrium. • Possess different functional groups. • Have no stabilization effect on the molecule. • Resonance • Shift in the position of electrons only. • Structures are arbitrary and do not exist. • Do not exist in equilibrium. • The functional group does not change. • Lower potential energy stabilize the molecule.

  17. Stereoisomerism Have the same molecular formula and structure but differ in the arrangement of atoms in space. Tautomerism Conformational Geometrical Optical

  18. CH3 H H H3C H3C H H CH3 H H H H Stereoisomerism Conformational Conformations of Butane (Sawhorse model)

  19. 1800 Newmann projection

  20. Stereoisomerism Conformations of Cycloalkanes

  21. H CO2H OH H OH H3C CO2H H OH OH CO2H CO2H Interconversions Fischer Sawhorse

  22. CH3 H Br H Br Br H Br CH3 H CH3 CH3 Interconversions

  23. CHO B H Br H Cl F CH2OH H Br H Cl CHO CH2OH Interconversions

  24. CO2H H OH CH3 Interconversions

  25. OH Ph Br CH3 Interconversions

  26. CO2H H OH H OH CH3 Interconversions

  27. Geometrical isomerism

  28. Geometrical isomerism Number of geometrical isomers =2x x = No. of double bonds For compounds with two different terminal groups Example No. of geometrical isomers =23=8

  29. For even no. of double bonds For odd no. of double bonds Geometrical isomerism For two identical terminal groups in alkene 3 geometrical isomers

  30. Optical isomerism Criterion for optical activity • Presence of chiral C–atom(for single asymmetric centre) For more than one asymmetric centres – • Non-superimposable mirror images Enantiomers (d,l–pair) Note: Superimposable mirror images Meso compounds

  31. CH3 CO2H H OH H Br H OH Br H CO2H CH3 Optical isomerism 2. No plane or centre of symmetry Plane of symmetry (Meso) No plane of symmetry (Enantiomer)

  32. CH3 H NH C C NH H CH3 Optical isomerism Centre of symmetry results optical inactivity

  33. Optical isomerism • When the molecule is asymmetrical: • Number of enantiomers = 2m • Number of meso isomers = 0 2. For symmetrical molecule with even number of asymmetric centres : Number of enantiomers = 2m–1

  34. Optical isomerism 3. For symmetrical molecule and odd number of asymmetric centres

  35. Thank you

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