1. Ch 24 From Petroleum to Pharmaceuticals Classes of Hydrocarbons

2. HydrocarbonsHydrocarbons AromaticAromaticAliphaticAliphatic

3. HydrocarbonsHydrocarbons AromaticAromaticAliphaticAliphatic AlkanesAlkanes AlkynesAlkynes AlkenesAlkenes

4. HydrocarbonsHydrocarbons AliphaticAliphatic AlkanesAlkanes Alkanes are hydrocarbons in which all of the bonds are single bonds. C C H H H HHH

5. HydrocarbonsHydrocarbons AliphaticAliphatic AlkenesAlkenes Alkenes are hydrocarbons that contain a carbon- carbon double bond. C C H H HH

6. HydrocarbonsHydrocarbons AliphaticAliphatic AlkynesAlkynes Alkynes are hydrocarbons that contain a carbon- carbon triple bond. HCCH

7. HydrocarbonsHydrocarbons AromaticAromatic The most common aromatic hydrocarbons are those that contain a benzene ring. H H H HHH

8. Reactive Sites in Hydrocarbons The Functional Group Concept

9. Functional Group a structural unit in a molecule responsible for its characteristic chemical behavior and its spectroscopic characteristics

10. AlkanesAlkanes functional group is a hydrogen atom the reaction that takes place is termed a substitution one of the hydrogens is substituted by some other atom or group, X R—H R—X

11. AlkanesAlkanes functional group is a hydrogen the reaction that takes place is substitution one of the hydrogens is substituted by some other atom or group R—H R—X + Cl 2 C C H H H HHH + HCl C C H Cl H HHH

12. Functional Groups in Hydrocarbons alkanesRH alkenes RH, double bond alkynes RH, triple bond aromaticsArH, double bond

13. Some Key Functional Groups

14. Families of organic compounds and their functional groups AlcoholsROH Alkyl halidesRX (X = F, Cl, Br, I) Aminesprimary amine: RNH 2 secondary amine: R 2 NH secondary amine: R 2 NH tertiary amine: R 3 N tertiary amine: R 3 N EthersROR

15. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Acyl group R

16. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Aldehyde R H

17. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Ketone R R'

18. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Carboxylic acid R OH

19. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Ester R OR'

20. Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Amide R NH 2

21. Introduction to Alkanes: Methane, CH 4 Ethane, C 2 H 6 Ethane, C 2 H 6 Propane, C 3 H 8 C n H 2n+2 General formula for an alkane

22. The simplest alkanes Methane (CH 4 ) CH 4 Ethane (C 2 H 6 )CH 3 CH 3 Propane (C 3 H 8 )CH 3 CH 2 CH 3 bp -160°C bp -89°C bp -42°C No isomers possible for C1, C2, C 3 hydrocarbons

23. Isomeric Alkanes: The Butanes C 4 H 10 General formula for any butane

24. n-Butane Isobutane CH 3 CH 2 CH 2 CH 3 (CH 3 ) 3 CH bp -0.4°C bp -10.2°C C 4 H 10

25. Higher n-Alkanes Pentane (C 5 H 12 ) and Beyond C n H 2n+2 n > 4

26. CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 n-Pentane n-Hexane CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 n-Heptane C n H 2n+2 n > 4

27. The C 5 H 12 Isomers

28. n-Pentane CH 3 CH 2 CH 2 CH 2 CH 3 Isopentane (CH 3 ) 2 CHCH 2 CH 3 Neopentane (CH 3 ) 4 C C 5 H 12

29. The number of isomeric alkanes increases as the number of carbons increase. There is no simple way to predict how many isomers there are for a particular molecular formula. How many isomers?

30. Table 2.3 Number of Constitutionally Isomeric Alkanes CH 4 1 C 2 H 6 1 C 3 H 8 1 C 4 H 10 2 C 5 H 12 3 C 6 H 14 5 C 7 H 16 9

31. Table 2.3 Number of Constitutionally Isomeric Alkanes CH 4 1 C 8 H 18 18 C 2 H 6 1 C 9 H 20 35 C 3 H 8 1 C 10 H 22 75 C 4 H 10 2 C 15 H 32 4,347 C 5 H 12 3 C 20 H 42 366,319 C 6 H 14 5 C 40 H 82 62,491,178,805,831 C 7 H 16 9

32. C 6 H 6 Isomers How many isomers with the composition C 6 H 6 can you draw?

33. C 6 H 6 Isomers: How many isomers with the composition C 6 H 6 can you draw?

34. Structure and Bonding in Alkenes

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

36.      Bonding in Ethylene Framework of  bonds Each carbon is sp 2 hybridized

37. Bonding in Ethylene Each carbon has a half-filled p orbital

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

39. Isomerism in Alkenes

40. IsomersIsomers Isomers are different compounds that have the same molecular formula (composition).

41. IsomersIsomers StereoisomersStereoisomers Constitutional isomers

42. IsomersIsomers StereoisomersStereoisomers different connectivity same connectivity; different arrangement of atoms in space

43. IsomersIsomers StereoisomersStereoisomers Constitutional isomers consider the isomeric alkenes of molecular formula C 4 H 8

44. 2-Methylpropene 1-Butene cis-2-Butene trans-2-Butene C CHH H CH 2 CH 3 H3CH3CH3CH3C C C CH 3 HH H C C H3CH3CH3CH3CH C C H H H3CH3CH3CH3C H3CH3CH3CH3C

45. 2-Methylpropene 1-Butene cis-2-Butene C CHH H CH 2 CH 3 H CH 3 C C H3CH3CH3CH3CH C C H H H3CH3CH3CH3C H3CH3CH3CH3C Constitutional isomers

46. 2-Methylpropene 1-Butene trans-2-Butene C CHH H CH 2 CH 3 H3CH3CH3CH3C C C CH 3 HH C C H H H3CH3CH3CH3C H3CH3CH3CH3C Constitutional isomers

47. cis-2-Butene trans-2-Butene H3CH3CH3CH3C C C CH 3 HH H C C H3CH3CH3CH3CH Stereoisomers

48. Molecular Chirality: Enantiomers

49. A molecule is chiral if its two mirror image forms are not superposable upon one another. A molecule is achiral if its two mirror image forms are superposable. ChiralityChirality

50. Br Cl H F It cannot be superposed point for point on its mirror image. Bromochlorofluoromethane is chiral

51. Br Cl H F H Cl Br F To show nonsuperposability, rotate this model 180° around a vertical axis. Bromochlorofluoromethane is chiral

52. Br Cl H F H Cl Br F

53. Another look

54. are enantiomers with respect to each other and nonsuperposable mirror images are called enantiomers EnantiomersEnantiomers

55. stereoisomers constitutionalisomers Isomers

56. stereoisomers constitutionalisomers geometric isomers (cis/trans)enantiomers(optical) Isomers

57. Chlorodifluoromethane is achiral

58. The two structures are mirror images, but are not enantiomers, because they can be superposed on each other. Chlorodifluoromethane is achiral

59. Symmetry in Achiral Structures

60. Symmetry tests for achiral structures Any molecule with a plane of symmetry must be achiral.

61. A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry. Plane of symmetry

62. A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry. Plane of symmetry

63. A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry. Plane of symmetry

64. A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry. Plane of symmetry

65. Physical Properties of Alkanes and Cycloalkanes

66. increase with increasing number of carbons more atoms, more electrons, more opportunities for induced dipole-induced dipole forces decrease with chain branching branched molecules are more compact with smaller surface area—fewer points of contact with other molecules Boiling Points

68. increase with increasing number of carbons more atoms, more electrons, more opportunities for induced dipole-induced dipole forces Boiling Points Heptane bp 98°C Octane bp 125°C Nonane bp 150°C

69. decrease with chain branching branched molecules are more compact with smaller surface area—fewer points of contact with other molecules Boiling Points Octane: bp 125°C 2-Methylheptane: bp 118°C 2,2,3,3-Tetramethylbutane: bp 107°C

70. Boiling Points of Alkanes governed by strength of intermolecular attractive forces alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absent only forces of intermolecular attraction are induced dipole-induced dipole forces

71. Induced dipole-Induced dipole attractive forces + – + – two nonpolar molecules center of positive charge and center of negative charge coincide in each

72. Induced dipole-Induced dipole attractive forces + – + – movement of electrons creates an instantaneous dipole in one molecule (left)

73. Induced dipole-Induced dipole attractive forces + – + – temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right)

74. Induced dipole-Induced dipole attractive forces + – + – temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right)

75. Induced dipole-Induced dipole attractive forces + – + – the result is a small attractive force between the two molecules

76. Induced dipole-Induced dipole attractive forces + – + – the result is a small attractive force between the two molecules

77. Straight chain hydrocarbonBranched hydrocarbon Lots of intermolecular contacts Fewer intermolecular contacts