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ALKENES

ALKENES. Hydrocarbons. Aliphatic. Aromatic. Alkanes. Alkenes. Alkynes. Alkene Nomenclature. Alkenes. Alkenes are hydrocarbons that contain a carbon-carbon double bond also called "olefins" characterized by molecular formula C n H 2n said to be "unsaturated". H 2 C. CH 2. H 2 C.

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ALKENES

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  1. ALKENES

  2. Hydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes

  3. Alkene Nomenclature

  4. Alkenes Alkenes are hydrocarbons that contain a carbon-carbon double bond also called "olefins" characterized by molecular formula CnH2n said to be "unsaturated"

  5. H2C CH2 H2C CHCH3 Alkene Nomenclature Propene (Propylene issometimes used but is not an acceptableIUPAC name) Ethene or Ethylene(both are acceptableIUPAC names)

  6. H2C CHCH2CH3 Alkene Nomenclature 1-Butene 1) Find the longest continuous chain that includes the double bond. 2) Replace the -ane ending of the unbranched alkane having the same number of carbons by -ene. 3) Number the chain in the direction that gives the lowest number to the doubly bonded carbon.

  7. H2C CHCHCH2Br CH3 Alkene Nomenclature 4) If a substituent is present, identify its position by number. The double bond takes precedence over alkyl groups and halogens when the chain is numbered. The compound shown above is4-bromo-3-methyl-1-butene.

  8. H2C CHCHCH2OH CH3 Alkene Nomenclature 4) If a substituent is present, identify its position by number. Hydroxyl groups take precedence over the double bond when the chain is numbered. The compound shown above is2-methyl-3-buten-1-ol.

  9. H2C H2C CH H2C CHCH2 H2C CCH3 Alkenyl groups methylene vinyl allyl isopropenyl

  10. Structure of Ethylene bond angles: H-C-H = 117° H-C-C = 121° bond distances: C—H = 110 pm C=C = 134 pm Planar

  11. Bonding in Ethylene • Side-by-side overlap of half-filled p orbitals gives a  bond

  12. Isomers Isomers are different compounds thathave the same molecular formula.

  13. H3C H CH2CH3 H C C C C H3C H H H H3C CH3 H H3C C C C C H H H CH3 1-Butene 2-Methylpropene trans-2-Butene cis-2-Butene

  14. H3C CH3 H H3C C C C C H H H CH3 Stereoisomers cis-2-Butene trans-2-Butene

  15. Stereochemical Notation cis (identical or analogous substituents on same side) trans (identical or analogous substitutents on opposite sides)

  16. + A—B B C A C C C Reactions of Alkenes The characteristic reaction of alkenes is addition to the double bond.

  17. H H H H     C C + H—H H H C C H H H H Hydrogenation of ethylene exothermic H° = –136 kJ/mol catalyzed by finely divided Pt, Pd, Rh, Ni

  18. B Y X A C C H H H H Mechanism of catalytic hydrogenation

  19.  – C C +E—Y C E C Y General equation for electrophilic addition

  20.  – C C +H—X C H C X When EY is a hydrogen halide

  21. Markovnikov’s Rule When an unsymmetrically substituted alkene reacts with a hydrogen halide, the hydrogen adds to the carbon that has the greater number of hydrogen substituents, and the halogen adds to the carbon that has the fewer hydrogen substituents.

  22. HBr CH3CH2CH CH3CH2CHCH3 CH2 acetic acid Br (80%) Markovnikov’s Rule Example

  23. + C C H—OH C H C OH Acid-Catalyzed Hydration of Alkenes reaction is acid catalyzed; typical hydration medium is 50% H2SO4-50% H2O

  24. Cyclopentene +Br2

  25. – Bromonium ion

  26. trans-Stereochemistry in vicinal dibromide

  27. O + C RCOOH C peroxy acid O + RCOH C C O Epoxidation of Alkenes

  28. Polymerization of alkenes cationic polymerization free-radical polymerization coordination polymerization

  29. H2C CH2 O2 peroxides 200 °C 2000 atm CH2 CH2 CH2 CH2 CH2 CH2 CH2 polyethylene Free-Radical Polymerization of Ethylene

  30. H2C CHCH3 CH CH CH CH CH CH CH CH3 H CH3 H H CH3 H polypropylene Free-Radical Polymerization of Propene

  31. H2C=CHCl  polyvinyl chloride H2C=CHC6H5  polystyrene F2C=CF2 Teflon

  32. Classes of Dienes

  33. C Classification of Dienes isolated diene conjugated diene cumulated diene

  34. C Nomenclature (2E,5E)-2,5-heptadiene (2E,4E)-2,4-heptadiene 3,4-heptadiene

  35. Isolated diene p bonds are independent of each other p orbitals overlap to give extended p bond encompassing four carbons Conjugated diene

  36. C C C Cumulated Dienes cumulated dienes are less stable thanisolated and conjugated dienes

  37. 118.4° 131 pm Structure of Allene linear arrangement of carbons nonplanar geometry

  38. 1,2-addition of XY 1,4-addition of XY Y Y X X 1,2-Addition versus 1,4-Addition

  39. Alkynes

  40. Hydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes

  41. Acetylene and ethyne are both acceptableIUPAC names for HC CH HC CCH3 HC CCH2CH3 Propyne 1-Butyne (CH3)3CC CCH3 4,4-Dimethyl-2-pentyne Nomenclature Higher alkynes are named in much the sameway as alkenes except using an -yne suffixinstead of -ene.

  42. 120 pm H C C H 106 pm 106 pm 121 pm C CH3 C H 146 pm 106 pm Structure linear geometry for acetylene

  43. s Bonds in Acetylene Each carbon isconnected to ahydrogen by as bond. The twocarbons are connectedto each other by as bond and two p bonds.

  44. C C H Acidity of Acetylene andTerminal Alkynes

  45. Reactions of Alkynes Acidity Hydrogenation Metal-Ammonia Reduction Addition of Hydrogen Halides Hydration Addition of Halogens Ozonolysis

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