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Chemistry

Chemistry. Properties of alkenes. Session objectives. Chemical reactions of alkene Addition of hydrogen, halogen, hydrogen halides Markownikoff’s rule Anti-Markownikoff’s rule Hydroboration-oxidation Oxymercuration-demercuration Oxidation of alkene Ozonolysis Conjugated dienes.

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Chemistry

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  1. Chemistry

  2. Properties of alkenes

  3. Session objectives • Chemical reactions of alkene • Addition of hydrogen, halogen, hydrogen halides • Markownikoff’s rule • Anti-Markownikoff’s rule • Hydroboration-oxidation • Oxymercuration-demercuration • Oxidation of alkene • Ozonolysis • Conjugated dienes

  4. Addition of Hydrogen The ease of hydrogenation Addition takes predominantly cis manner.

  5. Addition of Halogens Brown Colourless Test of unsaturation

  6. Mechanism Step I Step II stereospecific reaction

  7. Types of reaction Stereospecific reaction Stereoselective reaction Cis-isomer (major)

  8. Addition of hydrogen halides HI > HBr > HCI > HF

  9. Markownikoff’s rule Polar addition to an unsymmetrical alkene takes place in such a manner that the negative part of the addendum attaches to that carbon atom which is more highly substituted (or contains the least number of H atoms)

  10. Markownikoff’s rule

  11. Markownikoff’s rule If HBr is added to a symmetrical alkene, only one product is obtained. Markownikoff’s addition product depends on the stability of intermediate carbocation.

  12. Markownikoff’s rule

  13. Markownikoff’s rule Mechanism

  14. Markownikoff’s rule

  15. Peroxide effect (Anti Markownikoff’s addition) Mechanism:

  16. Addition of water (Hydration) Acid catalyzed addition of water

  17. Hydroboration–oxidation The addition is anti–Markownikoff

  18. Hydroboration–oxidation In a substituted cyclic alkene, a trans alcohol is formed.

  19. Oxymercuration–demercuration

  20. Oxidation of alkenes Test for unsaturation Baeyer’s test • This is also called Hydroxylation • cis-diol

  21. Oxidation of alkenes Cis- hydroxylation

  22. Oxidative cleavage of alkenes

  23. Oxidation with peroxide

  24. Ozonolysis of alkenes

  25. Do you know Write IUPAC name of alkene which on ozonolysis gives one molecule of propanal and one molecule of propanone

  26. Addition of methylenes

  27. Conjugated dienes (alkadienes)

  28. Conjugated dienes (alkadienes)

  29. Class exercise

  30. Class exercise 1 If singlet carbene is added to the ethylene, the product formed will be (a) propane (b) butane (c) cyclopropane (d) cyclobutane Solution: Cyclopropane Hence the answer is (c)

  31. Class exercise 2 Hydroboration-oxidation of 1-methyl cyclopentane will give (a) trans-1-methyl cyclopentan-2-ol (b) cis-1-methyl cyclopentan-2-ol(c) Mixture of (a) and (b) (d) 1-methylcyclopentan-1-ol Solution: cis-1-methyl cyclopentan-2-ol Hence the answer is (b)

  32. Class exercise 3 Anti-Markownikoff’s addition of HBr is not observed in (a) But-2-ene (b) Propene (c) But-1-ene (d) Pent-2-ene Solution: As but-2-ene is a symmetrical structure, we get same product while anti-Markownikoff’s rule applies. Hence the answer is (a)

  33. Class exercise 4 Electrophilic addition of Br2 to ethylene proceeds through (a) a transition state (b) a cyclic bromonium ion Solution: A three-centred cyclic bromonium ion is formed. Hence the answer is (a)

  34. Class exercise 5 Predict the major product of each of the following reaction. Solution:

  35. Class exercise 6 Predict the major product of each of the following reaction. Solution:

  36. Class exercise 7 Predict the major product of each of the following reaction. Solution:

  37. Class exercise 8 Write a mechanism for each of the following reaction. Solution:

  38. Class exercise 9 A hydrocarbon (R) adds one mole of hydrogen to form n-hexane . When R is oxidized vigorously with hot alk. KMnO4 followed by acid treatment it yields a single carboxylic acid containing 3 carbons. Give the structure of R Solution: R: CH3CH2CH = CHCH2CH3

  39. Class exercise 10 An organic compound (A) having molecular formula decolourizes bromine water.On hydrogenation (A) yields 2-methylbutane and reductive ozonolysis forms ethanal and propanone. What is A ? Solution:

  40. Thank you

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