1. Organic Chemistry: Saturated Hydrocarbons
Chapter 19
Organic Chemistry: Saturated Hydrocarbons
Organic chemistry is important in nanotechnology. A carbon nanotube forest is shown here.
Introduction to General, Organic, and Biochemistry, 10e
John Wiley & Sons, Inc
Morris Hein, Scott Pattison, and Susan Arena 1

2. Chapter Outline 19.1 Organic Chemistry: History and Scope
19.2 The Carbon Atom: Bonding and Shape
19.3 Organic Formulas and Molecular Models
19.4 Classifying Organic Compounds
19.5 Hydrocarbons
19.6 Saturated Hydrocarbons: Alkanes
19.7 Carbon Bonding in Alkanes 2 2

3. Chapter Outline 19.8 Isomerism 19.9 Naming Organic Compounds
19.10 Introduction to the Reactions of Carbon
19.11 Reactions of Alkanes
19.12 Sources of Alkanes
19.13 Gasoline: A Major Petroleum Product
19.14 Cycloalkanes
Chapter 19 Summary 3 3

4. Organic Chemistry: History and Scope
Organic chemistry is the study of compounds containing carbon.
These compounds occur naturally but can be prepared in a laboratory.
The early history of organic chemistry included an erroneous theory. (i.e. that organic compounds exist only in living organisms).
The German chemist Wöhler disproved this theory in 1828 with the laboratory synthesis of urea.

5. What is organic chemistry?
Carbon can form a vast array of long chain and ring containing compounds because carbon has the unique ability to bond to itself.
Organic compounds include drugs, fuels, toiletries, plastics, and fabrics. You can see why organic chemistry is such an important field of study.
Lipstick is made of organic molecules. Cosmetics and perfumes contain organic compounds. 5 5

6. The Carbon Atom: Bonding and Shape
Carbon can form saturated compounds (i.e. where all carbon atoms have four single bonds) or unsaturated compounds (i.e. at least one carbon has a double bond (C=C) or a triple bond (C≡C)).

7. The Carbon Atom: Bonding and Shape
These are the molecular shapes of carbon compounds predicted by the VSEPR Bonding Theory.

8. The Carbon Atom: Bonding and Shape
This figure shows the bonding shape that results when carbon has four single bonds.
Figure 19.1 Tetrahedral structure of carbon: (a) a regular tetrahedron; (b) a carbon atom with tetrahedral bonds; (c) a carbon atom within a regular tetrahedron; (d) a methane molecule, CH4

9. Your Turn!
Estimate the bond angles around 1C and 2C in the following structure. 9 9

10. Your Turn!
Estimate the bond angles around 1C and 2C in the following structure. 10 10

11. Organic Formulas and Molecular Models
Structural formulas or models are often used in organic chemistry to illustrate molecules.
For example,
or in the case of a model.

12. Figure 19.3 Types of formulas and models used to represent organic molecules. Each diagram is a representation of a propane molecule. 12 12

13. Organic Formulas and Molecular Models
This is an example of how to change a condensed structural formula into a line structure.
The table on the next slide summarize formulas and models used in organic chemistry.

14. Formula or model Definition
Lewis structure
Structural formula
Condensed structural formula
Line structure
Ball-and-stick model
Space-filling model
Shows all bonds, all atoms, and all nonbonding electrons
Same as Lewis structure except nonbonding electrons are not shown
Bonds are collapsed so relative positions
of atoms are group together
Only bonds and functional groups are shown and each endpoint and bend represents a carbon atom
Atoms are shown as balls and bonds as sticks
and the shape is shown at the central atom.
Bonds are omitted and the size of atoms are emphasized.

15. Classifying Organic Compounds
Functional groups are group of atoms (or one atom) that have specific behavioral characteristics in organic compounds.
Organic compounds are classified based on the functional groups that they contain. 15 15

16. Classifying Organic Compounds
The list of common functional groups found in organic compounds are shown here on Table 19.1. 16 16

17. Classifying Organic Compounds
The list of important functional groups found in biological compounds is shown here on Table 19.2. 17 17

18. Classifying Organic Compounds
Ethanol contains the alcohol functional group and dimethyl ether contains the ether functional group. They have the same molecular formula but the boiling point (b.p.) of ethanol is 78C while the b.p. of dimethyl ether is -23C because of the structural differences between the molecules. 18 18

19. Hydrocarbons
Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms. (e.g. propane, CH3CH2CH3 is a hydrocarbon but ethanol, CH3CH2OH is not).
Hydrocarbons are classified as either aliphatic (i.e those hydrocarbons without benzene rings in the chemical structure) or aromatic.(i.e those hydrocarbons with benzene rings in the chemical structure) as shown in Figure 19.4 on the next slide.
Hydrocarbons are also classified as saturated or unsaturated compounds.

20. Figure 19.4 Classes of Hydrocarbons

21. Hydrocarbons
The principal source of hydrocarbons is fossil fuels which include natural gas, petroleum, and coal.
Fossil fuels are the primary source of heat and also a primary source of organic chemicals.

22. Saturated Hydrocarbons: Alkanes
Alkanes are saturated hydrocarbons that are either straight- chain or branched-chain hydrocarbons.

23. Saturated Hydrocarbons: Alkanes
Alkanes form a homologous series of straight-chain molecules as seen in Table 19.3 on the next slide. Members of a homologous series have similar structures but different chemical formulas.
The general formula for all non-cyclic alkanes is shown here.

24. Saturated Hydrocarbons: Alkanes24 24

25. Your Turn! Write the formula for an alkane that has nine carbon atoms.
Write the condensed structural formula for the straight-chain alkane that has nine carbon atoms. 25 25

26. Your Turn! Write the formula for an alkane that has nine carbon atoms.
CnH2n+2 = C9H20
Write the condensed structural formula for the straight-chain alkane that has nine carbon atoms.
CH3CH2CH2CH2CH2CH2CH2CH2CH3 26 26

27. Carbon Bonding in Alkanes
Alkanes contain saturated carbon atoms that have four sigma bonds.
Sigma bonds are linear bonds formed by a pair of electrons in overlapping atomic orbitals. 27 27

28. Carbon Bonding in Alkanes
Carbon has the ability to form four sigma bonds because of its ability to hybridize its valence shell electron orbitals (i.e the s and the 2p orbitals) as shown in Figure 19.5 on the next slide. 28 28

29. Carbon Bonding in Alkanes
Figure 19.5 Rearrangement of carbon 2s and 2p orbitals to form four equivalent sp3 hybrid orbitals.

30. Carbon Bonding in Alkanes
Figure 19.6 shows the tetrahedral nature of the sp3-hybridized orbitals.
Figure 19.6 (a) A single sp3-hybridized orbital; (b) four sp3-hybridized orbitals in a tetrahedral arrangement; (c) sp3 and s orbitals overlapping to form four C-H sigma bonds in methane.

31. Isomerism
The properties of an organic substance are dependent on its molecular structure. The majority of organic compounds are made up of relatively few elements: carbon, hydrogen, oxygen, nitrogen, and the halogens.
The valence bonds or points of attachment may be represented in structural formulas by a corresponding number of dashes attached to each atom. 31 31

32. Isomerism
Carbon can form four single bonds each, nitrogen can form three single bonds, oxygen can only form two single bonds, and hydrogen and the halogens can form one single bond each. 32 32

33. Isomerism
Because carbon can form four single bonds, alkanes with four or more carbon atoms can form isomers.
Isomers are molecules that have the same molecular formula but different structural formula.

34. Isomerism
For example, it is possible to write two structural formulas corresponding to the molecular formula C4H10 (i.e., butane and isobutane are isomers of each other). Notice the ball-and-stick models of these molecules on the next slide. 34 34

35. Figure 19.7 Ball-and-stick models illustrating the structural formulas of several alkanes.35 35

36. Your Turn!
There are several isomers of heptane, C7H16. Draw structural formulas and condensed structural formulas for the two isomers that only have one branching methyl group. 36 36

37. Your Turn!
There are several isomers of heptane, C7H16. Draw structural formulas and condensed structural formulas for the two isomers that only have one branching methyl group. 37 37

38. Naming Organic Compounds
How do chemists name organic compounds?
Organic compounds are named using the IUPAC System (International Union of Pure and Applied Chemistry).
The IUPAC System was developed at an international science meeting in Geneva in 1892.
The IUPAC System is essentially a set of rules that allow for a systematic and uniform method of naming compounds.

39. Naming Alkyl Groups
Alkyl groups have one hydrogen less than the respective alkane.
The general formula for alkyl groups is shown here and a list of alkyl groups are shown in Table 19.4.

40. Naming Alkyl Groups

41. Naming Organic Compounds
Carbon atoms are often classified based on the number of carbon atoms directly attached to them.
Primary (1)
Secondary (2)
Tertiary (3)
A carbon with one carbon attached
A carbon with two carbons attached
A carbon with three carbons attached

42. Naming Organic Compounds
Here is an example of a molecule with all three types of carbon atoms. 42 42

43. Your Turn!
Identify all the carbon atoms in the structure below as 1o, 2o or 3o. 43 43

44. Your Turn!
Identify all the carbon atoms in the structure below as 1o, 2o or 3o. 44 44

45. IUPAC Rules for Naming Alkanes
1. Identify and then name the longest continuous chain of carbon atoms. The longest chain in this molecule contains six carbon atoms. 45

46. IUPAC Rules for Naming Alkanes
2. Number the chain so any branch alkyl groups have the lowest possible number. There is only one correct way to number the carbon atoms in the longest chain. 46

47. IUPAC Rules for Naming Alkanes
3. The methyl group is attached to the #3 carbon atom not the #4 carbon atom. The IUPAC name for the molecule is 3-methylhexane. 47

48. IUPAC Rules for Naming Alkanes
4. Use prefixes (i.e. di, tri, tetra etc. ) if two or more of the same alkyl group branches appear on the longest chain. One methyl group is on the #2 carbon atom and another methyl group is on the #3 carbon atom. 48

49. IUPAC Rules for Naming Alkanes
5. When several different groups are attached to the same parent compound, list the groups in alphabetical order (e.g. chloro is listed before isopropyl and isopropyl is listed before methyl). 49

50. Your Turn!
Give the IUPAC name for the this alkane. 50

51. Your Turn!
Give the IUPAC name for the this alkane.
2-methylhexane 51

52. Your Turn!
Write the structural formula for 5-ethyl-3-methyloctane. 52

53. Your Turn!
Write the structural formula for 5-ethyl-3-methyloctane. 53

54. Introduction to the Reactions of Carbon
The importance of organic chemistry is illustrated by the variety of reactions that occur at the carbon atom which include four major types.
Oxidation-reduction
Substitution
Addition
Elimination 54 54

55. Introduction to the Reactions of Carbon
Oxidation involves a higher number of oxygen atoms bonding to carbon. Carbon dioxide is more oxidized than methane so this is an oxidation reaction. 55 55

56. Introduction to the Reactions of Carbon
Reduction is the reverse of oxidation and involves a higher number of hydrogen atoms bonding to carbon. Methanol is more reduced than carbon dioxide so this is a reduction.

57. Introduction to the Reactions of Carbon
Substitution is the exchange of one atom for another at the carbon atom.
In this reaction a bromine atom changes position with a hydrogen atom in methane. 57 57

58. Introduction to the Reactions of Carbon
Addition is a reaction where two reactants join to form a single product. 58 58

59. Introduction to the Reactions of Carbon
Elimination is the splitting of a single reactant into two products. 59 59

60. Your Turn!
Classify the following reaction as substitution, elimination or addition. 60 60

61. Your Turn!
Classify the following reaction as substitution, elimination or addition.
Elimination 61 61

62. Reactions of Alkanes Reaction Class Name of Reaction Oxidation
Substitution
Elimination
Decomposition
Rearrangement
Combustion
Halogenation
Dehydrogenation
Cracking
Isomerization
Reactions of alkanes can be classified as shown in
this table. 62 62

63. Reactions of Alkanes Combustion (oxidation)
Alkanes are a valuable energy source due to their ability to react with oxygen . Alkanes release a large amount of energy as shown here.
Alkanes generally are considered to be unreactive and for reactions other than combustion a catalyst or other special reaction conditions are necessary.

64. Reactions of Alkanes
Halogenation (substitution): Here a chlorine atom is replacing a hydrogen atom on an ethane molecule.

65. Reactions of Alkanes
Dehydrogenation (elimination): Here two hydrogen atoms are removed from a propane molecule to form propene. 65 65

66. Reactions of Alkanes
Cracking (decomposition): Here an alkane undergoes decomposition to form a smaller alkane and an alkene. 66 66

67. Reactions of Alkanes
Isomerization (rearrangement): Here an unbranched alkane (pentane) undergoes isomerization to form a branched compound that is an isomer of pentane (2-methylbutane). 67 67

68. The chlorination of methane with excess chlorine can produce each of the compounds shown in Table 19.5.

69. Reactions of Alkanes
Alkyl halides are compounds that have an X (X = -F (fluoro), -Cl (chloro), -Br (bromo), or - I (iodo) attached to a carbon atom.
RX is the general formula for alkyl halides.

70. Reactions of Alkanes
Examples of Alkyl Halides 70 70

71. Reactions of Alkanes
The mechanism of halogenation consists of three steps: initiation, propagation, and termination as shown on the next few slides.
A mechanism is the individual steps that lead to the product from the reactant.
Overall Reaction 71 71

72. Reactions of Alkanes
Step I Initiation: Formation of chlorine free radicals. 72 72

73. Reactions of Alkanes
Step II Propagation: A chlorine free radical reacts with the alkane to form hydrogen chloride and an alkyl free radical. The alkyl free radical reacts with a molecule of chlorine to form another chlorine free radical and an alkyl halide. 73 73

74. Reactions of Alkanes
Step III Termination: 1) The reaction of two chlorine free radicals; 2) the reaction of a chlorine free radical and an alkyl free radical to form an alky halide; 3) the reaction of two alkyl free radicals to form a larger alkane. 74 74

75. Free Radical Stability and Reactivity
Experimental results show that tertiary (3o) free radicals are the most stable and the most easily formed radicals in chemical reactions. 75 75

76. Free Radical Stability and Reactivity
Secondary (2o) free-radicals are next in stability and primary (1o) free radicals are the least stable. 76 76

77. Free Radical Stability and Reactivity
Therefore the major product formed in the chlorination of propane corresponds to the secondary free radical, i.e. 2-chloropropane. The minor product corresponds to the primary free radical. 77 77

78. Your Turn!
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane. 78 78

79. Your Turn!
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Initiation 79 79

80. Your Turn!
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Propagation 80 80

81. Your Turn!
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Termination 81 81

82. Sources of Alkanes
Alkanes are produced from natural gas and petroleum.
Natural gas and petroleum are formed by the decay of plants and animals
Natural gas and petroleum are non-renewable sources of energy.

83. Gasoline: A Major Petroleum Product
Gasoline is a mixture of hydrocarbons. Without additives it causes knocking which is a detonation of the air-fuel mixture in an engine.
Figure Uses of petroleum
The octane rating of gasoline is the knocking performance based on the percent isooctane in an isooctane/heptane mixture. (higher octane ratings = less knocking)

84. Gasoline: A Major Petroleum Product
Manufacturers of gasoline have switched from tetraethyl lead to more environmentally friendly additives like MTBE (methyl-tert-butyl ether) and ethanol. 84 84

85. Gasoline: A Major Petroleum Product
These additives boost octane ratings like lead additives but are better for the environment. However studies have shown that MTBE can pollute ground water and is also being replaced. 85 85

86. Cycloalkanes
Cycloalkanes are cyclic alkanes with the general formula CnH2n.

87. Cycloalkanes
The physical properties and the chemical reactivity of cycloalkanes are similar to their open-chain counterparts (the alkanes) with two exceptions. Cyclopropane and cyclobutane are more reactive.

88. Cycloalkanes
Cyclopropane and cyclobutane have higher reactivity because their bonds are strained. The basis for the strain is the deviation of their bond angles from the normal tetrahedral carbon bond angle of 109.5. 88 88

89. Cycloalkanes
These molecules cannot change shape to significantly change their bond angles like cycloalkanes that have larger ring sizes. 89 89

90. Cycloalkanes
The result of the bond strain in cyclopropane is that it reacts readily with molecules like bromine as shown here. 90 90

91. Figure Ball-and-stick models of cyclopropane, hexane, and cyclohexane. In cyclopropane, all the carbon atoms are in one plane (bond angles = 60° instead of 109.5° ).

92. The cyclohexane molecule is puckered (as shown in the chair conformation) with bond angles about 109.5° as found in hexane. 92 92

93. Cycloalkanes
Cyclohexane can exist in either the chair or boat conformation.
A conformation is the three-dimensional spatial arrangement of the atoms in a molecule.

94. Cycloalkanes
Figure Conformations of cyclohexane: (a) chair conformation; (b) boat conformation. Axial hydrogens are shown in blue in the chair conformation. 94 94

95. Cycloalkanes When naming monosubstituted cycloalkanes:
1. Name the substituent
2. Name the parent cyclohexane
Both of these structures are the same molecule and have the same name (methylcyclohexane).
methyl cyclohexane = methylcyclohexane

96. Cycloalkanes When naming polysubstituted cycloalkanes.
Number the ring (clockwise or counterclockwise) to give the substituted groups the lowest possible numbers.
Name the groups and their locations.
Name the parent cyclohexane. 96 96

97. Cycloalkanes 97 97

98. Your Turn!
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane. 98 98

99. Your Turn!
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane.
1-bromo-2-methylcyclopentane 99 99

100. Your Turn!
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane.
1,1-dichloro-3-ethylcyclohexane
100
100

101. Chapter 19 Summary
Organic chemistry is the chemistry of carbon compounds.
Alkanes are hydrocarbons that are either saturated (no double or triple bonds) or unsaturated (one or more multiple bonds ).
Organic compounds are classified by functional groups which is the smaller part of the molecule that determines the chemical profile of the molecule.

102. Chapter 19 Summary
Organic molecules can be represented by ball-and stick models, space-filling models, Lewis structures, line structures, and condensed structural formulas.
Saturated carbon atoms are sp3 hybridized which form can four sigma bonds.
102
102

103. Chapter 19 Summary
Reactions of organic molecules are classified as oxidation-reduction, substitution, elimination, and addition.
Alkanes undergo combustion but need special reaction conditions to undergo halogenation, dehydrogenation, cracking, and isomerization.

104. Chapter 19 Summary
Cycloalkanes (CnH2n ) exist in conformations with hydrogen on each carbon in axial or equatorial position
Cyclopropane and cyclobutane are unusually reactive because of strained bonds.
The most stable form of cyclohexane is the chair conformation.
104
104