1. 3. Organic Compounds: Alkanes and Their Stereochemistry
Why this Chapter
Alkanes are unreactive, but provide useful vehicle to introduce important ideas about organic compounds
Alkanes will be used to discuss basic approaches to naming organic compounds
We will take an initial look at 3-D aspects of molecules

2. 3.1 Functional Groups
Functional group - collection of atoms at a site that have a characteristic behavior in all molecules where it occurs
The group reacts in a typical way, generally independent of the rest of the molecule
For example, the double bonds in simple and complex alkenes react with bromine in the same way

3. Functional Groups with: Multiple Carbon–Carbon Bonds
Alkenes have a C-C double bond
Alkynes have a C-C triple bond
Arenes have special bonds that are represented as alternating single and double C-C bonds in a six-membered ring

4. Alkenes and Alkynes
Alkenes contain a double bond between adjacent carbon atoms.
Alkynes contain a triple bond.
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5. Functional Groups with: Carbon Singly Bonded to an Electronegative Atom

6. Alcohols and Ethers
An alcohol contains the hydroxyl (-OH) functional group.
In an ether, an oxygen atom is bonded to two carbon atoms
–C–O–C– .
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7. Functional Groups with: Carbon–Oxygen Double Bond (Carbonyl Groups)

8. Aldehydes and Ketones
An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen.
In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms.
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9. Carboxylic Acids and Esters
Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. O 
— C—OH
An ester contains the carboxyl group between carbon atoms.
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10. Amines and Amides In amines, the functional group is a nitrogen atom.|
—N —
In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group.
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11. Summary of Functional Groups

12. Survey of Functional Groups

13. Survey of Functional Groups

14. Functional Groups in Everyday Items
Methyl amine (fish)
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15. Learning Check 1) CH3–CH2–CH2–OH 2) CH3–O–CH2–CH3 3) CH3–CH2–NH2 O O
Classify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine.
1) CH3–CH2–CH2–OH
2) CH3–O–CH2–CH3
3) CH3–CH2–NH2
O O
|| ||
4) CH3–C–OH 5) CH3–C–O–CH3

16. Solution 1) CH3─CH2─CH2─OH 2) CH3─O─CH2─CH3 alcohol ether
Classify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine.
1) CH3─CH2─CH2─OH 2) CH3─O─CH2─CH3
alcohol ether
3) CH3─CH2─NH2 amine
O O
|| ||
4) CH3─C─OH 5) CH3─C─O─CH3
carboxylic acid ester

17. Learning Check
What functional group is not present in the naturally occurring compound shown below?
carboxylic acid
amine
primary alcohol
secondary alcohol
methyl group

18. Solution
What functional group is not present in the naturally occurring compound shown below?
carboxylic acid
amine
primary alcohol
secondary alcohol
methyl group

19. 3.2 Alkanes and Alkane Isomers
Alkanes: Compounds with C-C single bonds and C-H bonds only (no functional groups)
Connecting carbons can lead to large or small molecules
The formula for an alkane with no rings in it must be CnH2n+2 where the number of C’s is n
Alkanes are saturated with hydrogen (no more can be added
They are also called aliphatic compounds

21. Condensed Structures of Alkanes
We can represent an alkane in a brief form or in many types of extended form
A condensed structure does not show bonds but lists atoms, such as
CH3CH2CH2CH3 (butane)
CH3(CH2)2CH3 (butane)

22. Expanded and Condensed Structures

23. Some Structures for Butane
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24. Line-Bond Formulas
Because each C atom has a tetrahedral arrangement, the order of atoms is not a straight line, but a zigzag pattern.
A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds from carbon atom to carbon atom.

25. Hexane has Six Carbon Atoms
Is an alkane with 6 carbon atoms in a continuous chain.
Has a “zig-zag” look because each carbon atom is at the center of a tetrahedron.
Is represented by a ball-and-stick model as

26. Learning Check A. Write the condensed formula for: H H H H H
H C C C C C H
H H H H H
B. What is its molecular formula?
C. What is its name?

27. Solution CH3CH2CH2CH2CH3 C5H12 pentane
A. Write the condensed formula for:
H H H H H
H C C C C C H
H H H H H
B. What is its molecular formula?
C. What is its name?
CH3CH2CH2CH2CH3
C5H12
pentane

28. Learning Check Write the condensed structural formula for A. ethane
B. heptane

29. Solution Write the condensed structural formula for A. ethane CH3─CH3
B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3

30. Alkane Isomers CH4 = methane, C2H6 = ethane, C3H8= propane
The molecular formula of an alkane with more than three carbons can give more than one structure
C4 (butane) = butane and isobutane
C5 (pentane) = pentane, 2-methylbutane, and 2,2- dimethylpropane
Alkanes with C’s connected to no more than 2 other C’s are straight-chain or normal alkanes
Alkanes with one or more C’s connected to 3 or 4 C’s are branched-chain alkanes

31. Constitutional Isomers
Isomers that differ in how their atoms are arranged in chains are called constitutional isomers
Compounds other than alkanes can be constitutional isomers of one another
They must have the same molecular formula to be isomers

32. Isomers of Butane Isomers Have the same molecular formula.
Have different atom arrangements.
Of butane (C4H10) consist of a straight chain and a branched chain each with 4 carbon atoms.
branch

34. What kind of carbon is not present in the molecule below?
Learning Check
What kind of carbon is not present in the molecule below?
primary
secondary
tertiary
quaternary
All 4 kinds of carbon are present

35. What kind of carbon is not present in the molecule below?
Solution
What kind of carbon is not present in the molecule below?
primary
secondary
tertiary
quaternary
All 4 kinds of carbon are present

36. How many secondary hydrogens are there in the following molecule?
Learning Check
How many secondary hydrogens are there in the following molecule? 2 3 4 5 6

37. How many secondary hydrogens are there in the following molecule?
Solution
How many secondary hydrogens are there in the following molecule? 2 3 4 5 6

38. Which of the following choices is not an alkane?
Learning Check
Which of the following choices is not an alkane?
C12H26
C10H20
C11H24
C16H34
C20H42

39. Which of the following choices is not an alkane?
Solution
Which of the following choices is not an alkane?
C12H26
C10H20
C11H24
C16H34
C20H42

40. Learning Check
A brilliant chemist determined the number of secondary carbons and secondary hydrogens for an unknown alkane. Well, actually, the chemist is having trouble deciding which numbers are correct. Which of these answers is possible for an alkane?
2° hydrogens
2° carbons

41. Solution
A brilliant chemist determined the number of secondary carbons and secondary hydrogens for an unknown alkane. Well, actually, the chemist is having trouble deciding which numbers are correct. Which of these answers is possible for an alkane?
2° hydrogens
2° carbons

42. 3.4 Naming Alkanes
Compounds are given systematic names by a process that uses
Follows specific rules
Find parent hydrocarbon chain
Carbons in that main chain are numbered in sequence
Substituents are identified numbered
Write compound name is single word
Name a complex substituents as though it were a compound itself
See specific examples in text

43. IUPAC Names for Simple Alkanes
Use a prefix to indicate the number of carbons in a chain.
End in –ane.
The names of organic compounds are determined by the IUPAC rules (International Union of Pure and Applied Chemistry). The stem of the name states the number of carbon atoms in the carbon chain of the compounds. The suffix, in this case –ane, indicates the alkane family.

44. Learning Check A. Give the name of each compound: 1) CH3—CH3
2) CH3—CH2—CH3
3) CH3—CH2—CH2—CH2—CH2—CH3
B. Write the condensed structural formula of
pentane.

45. Solution A. Give the name of each compound: 1) CH3—CH3 ethane
2) CH3—CH2—CH3 propane
3) CH3—CH2—CH2—CH2—CH2—CH3
hexane
B. Write the condensed structural formula of pentane.
CH3—CH2—CH2—CH2—CH3

46. 3.3 Alkyl Groups
Alkyl group – remove one H from an alkane (a part of a structure)
General abbreviation “R” (for Radical, an incomplete species or the “rest” of the molecule)
Name: replace -ane ending of alkane with -yl ending
CH3 is “methyl” (from methane)
CH2CH3 is “ethyl” from ethane

48. Types of Alkyl groups
Classified by the connection site (See Figure 3.3)
a carbon at the end of a chain (primary alkyl group)
a carbon in the middle of a chain (secondary alkyl group)
a carbon with three carbons attached to it (tertiary alkyl group)

49. Naming Substituents IUPAC Common methyl ethyl propyl n-propyl
Isopropyl
butyl
n-butyl
1-methylpropyl
sec-butyl
2-methylpropyl
Isobutyl
1,1-dimethylethyl
tert-butyl or
t-butyl

50. Naming Substituents IUPAC Common pentyl n-pentyl or amyl 1-methylbutyl
sec-pentyl
3-methylbutyl
isopentyl or
isoamyl or i-amyl
1,1-dimethylpropyl
tert-pentyl or
tert-amyl or t-amyl
2,2-dimethylpropyl
neopentyl

51. Naming Substituents
IUPAC
Fluoro
Chloro
Bromo
Iodo
Hydroxy

52. Alkanes with Alkyl Groups
methylpropane
methyl groups
2,4-dimethylpentane

53. Learning Check
Write three isomers of C5H12 and name each.

54. Solution Write three isomers of C5H12 and name each.
A chain of 5 carbon atoms CH3─CH2─CH2─CH2─CH3
pentane
A chain of 4 carbon atoms and 1 carbon branch
CH3 │
CH3─CH─CH2─CH methylbutane
A chain of 3 carbon atoms and 2 carbon branches
CH3─C─CH3 2,2-dimethylpropane

55. What is the best IUPAC name for the following compound?
Learning Check
What is the best IUPAC name for the following compound?
2-ethyl-3-isopropylhexane
1-isopropyl-3-ethylhexane
4-isopropyl-5-ethylhexane
3-methyl-4-isopropylheptane
4-isopropyl-3-methylheptane

56. What is the best IUPAC name for the following compound?
Solution
What is the best IUPAC name for the following compound?
2-ethyl-3-isopropylhexane
1-isopropyl-3-ethylhexane
4-isopropyl-5-ethylhexane
3-methyl-4-isopropylheptane
4-isopropyl-3-methylheptane

57. What is the systematic name of the alkane shown below?
Learning Check
What is the systematic name of the alkane shown below?
3,7-dimethyl-4-propyloctane
2-methyl-5-(1-methylpropyl)octane
2-ethyl-6-methyl-3-propylheptane
3-methyl-4-(3-methylbutyl)heptane
2,6-dimethyl-5-propyloctane

58. What is the systematic name of the alkane shown below?
Solution
What is the systematic name of the alkane shown below?
3,7-dimethyl-4-propyloctane
2-methyl-5-(1-methylpropyl)octane
2-ethyl-6-methyl-3-propylheptane
3-methyl-4-(3-methylbutyl)heptane
2,6-dimethyl-5-propyloctane

59. Which of the following is not an isomer of hexane?
Learning Check
Which of the following is not an isomer of hexane?
2,2-dimethylbutane
2,2-dimethylpentane
3-methylpentane
2-methylpentane
2,3-dimethylbutane

60. Which of the following is not an isomer of hexane?
Solution
Which of the following is not an isomer of hexane?
2,2-dimethylbutane
2,2-dimethylpentane
3-methylpentane
2-methylpentane
2,3-dimethylbutane

61. How many constitutional isomers of C4H10O are alcohols?
Learning Check
How many constitutional isomers of C4H10O are alcohols? 1 2 3 4 5

62. How many constitutional isomers of C4H10O are alcohols?
Solution
How many constitutional isomers of C4H10O are alcohols? 1 2 3 4 5

63. 3.5 Properties of Alkanes
Called paraffins (low affinity compounds) because they do not react as most chemicals
They will burn in a flame, producing carbon dioxide, water, and heat

64. Crude Oil The hydrocarbons in crude oil are
Separated by boiling points.
Heated to higher temperatures to produce gases that can be removed and cooled.
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65. Combustion of Alkanes Alkanes
Undergo combustion by reacting with oxygen to produce carbon dioxide, water, and energy.
Are typically not very reactive due to strong C-C single bonds.
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alkane + O CO2 + H2O + energy

66. Learning Check Propane is used to provide heat for
cooking or warming a room. Write a
balanced equation for the complete
combustion of propane.
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67. Learning Check Solution Propane is used to provide heat for
cooking or warming a room. Write a
balanced equation for the complete
combustion of propane.
Solution
C3H8 + 5O CO2 + 4H2O
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68. Learning Check
Write a balanced equation for the reaction for the complete combustion of:
heptane
ethane

69. Solution
Write a balanced equation for the reaction for the complete combustion of:
heptane C7H16.
ethane
C7H O2  CO2 + 8H2O
2C2H O2  4CO H2O

70. Properties of Alkanes
They react with Halogens like Cl2 in the presence of light to replace H’s with Cl’s (not controlled)

71. Learning Check
Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.

72. Solution CH3—CH2—CH2— Br 1-bromopropane; propyl bromide Br |
Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.
CH3—CH2—CH2— Br
1-bromopropane; propyl bromide Br |
CH3—CH—CH3
2-bromopropane; isopropyl bromide

73. Physical Properties
Boiling points and melting points increase as size of alkane increases
Dispersion forces increase as molecule size increases, resulting in higher melting and boiling points

74. 3.6 Conformations of Ethane
Stereochemistry concerned with the 3-D aspects of molecules
 bonds are cylindrically symmetrical
Rotation is possible around C-C bonds in open-chain molecules

75. Conformers
Conformation- Different arrangement of atoms resulting from bond rotation
Conformations can be represented in 2 ways:

76. Torsional Strain We do not observe perfectly free rotation
There is a barrier to rotation, and some conformers are more stable than others
Staggered- most stable: all 6 C-H bonds are as far away as possible
Eclipsed- least stable: all 6 C-H bonds are as close as possible to each other

78. 3.7 Conformations of Other Alkanes
The eclipsed conformer of propane has 3 interactions: two ethane-type H-H interactions, and one H-CH3 interaction

79. Conformations of Other Alkanes
• Conformational situation is more complex for larger alkanes
• Not all staggered conformations has same energy, and not all
eclipsed conformations have same energy

80. Conformations of Butane
Anti conformation- methyl groups are 180˚ apart
Gauche conformation- methyl groups are 60˚ apart
Which is the most energetically stable?

82. Steric Strain
Steric strain- repulsive interaction occurring between atoms that are forced closer together than their atomic radii allow 11 6
3.8 6 4 4 4

83. Learning Check
What is the correct order of stability, starting with the most strained, for the conformations shown below?
A B, C
A, C, B
B, A, C
C, A, B
C, B, A

84. Solution
What is the correct order of stability, starting with the most strained, for the conformations shown below?
A B, C
A, C, B
B, A, C
C, A, B
C, B, A

85. Learning Check
C6H14 has 5 isomers. How many of these isomers have at least one tertiary carbon? 1 2 3 4

86. Solution
C6H14 has 5 isomers. How many of these isomers have at least one tertiary carbon? 1 2 3 4

87. Learning Check
Which statement about bond rotations around C-C bonds in ethane and ethylene is correct?
Rotation around σ bond is easy because the orbital overlap does not change with rotation.
Rotation around π bond is easy because there are p orbitals available in all directions of space.
Rotation around σ bond is very hard because the electron pairs from the adjacent bonds must pass by each other.
Rotation around π bond is hard because the electrons are delocalized.

88. Solution
Which statement about bond rotations around C-C bonds in ethane and ethylene is correct?
Rotation around σ bond is easy because the orbital overlap does not change with rotation.
Rotation around π bond is easy because there are p orbitals available in all directions of space.
Rotation around σ bond is very hard because the electron pairs from the adjacent bonds must pass by each other.
Rotation around π bond is hard because the electrons are delocalized.

89. Learning Check
Which of the above represents the Newman projection of 2-bromo-3-chlorobutane? a b c d e

90. Solution
Which of the above represents the Newman projection of 2-bromo-3-chlorobutane? a b c d e

91. Learning Check 3.8 kJ/mol 4.0 kJ/mol 6.0 kJ/mol 0.0 kJ/mol 11.0 kJ/mol
The lowest energy conformation of decane resembles a straight rod. It is a fully stretched “zig-zag” conformation with all bonds staggered and all large substituents anti to each other. Imagine we bend this chain at carbon 5. What is the minimum strain that such a once-bent conformation (bent rod) must have?
3.8 kJ/mol
4.0 kJ/mol
6.0 kJ/mol
0.0 kJ/mol
11.0 kJ/mol

92. Solution 3.8 kJ/mol 4.0 kJ/mol 6.0 kJ/mol 0.0 kJ/mol 11.0 kJ/mol
The lowest energy conformation of decane resembles a straight rod. It is a fully stretched “zig-zag” conformation with all bonds staggered and all large substituents anti to each other. Imagine we bend this chain at carbon 5. What is the minimum strain that such a once-bent conformation (bent rod) must have?
3.8 kJ/mol
4.0 kJ/mol
6.0 kJ/mol
0.0 kJ/mol
11.0 kJ/mol

93. Learning Check the energy of one gauche interaction
What is the energy difference between the two lowest-energy conformations of 2,3-dimethylbutane?
the energy of one gauche interaction
the energy of two gauche interactions
the energy of two H ↔ CH3 eclipsing interactions
the energy of three H ↔ CH3 eclipsing interactions
the energy of two CH3 ↔ CH3 eclipsing interactions

94. Solution the energy of one gauche interaction
What is the energy difference between the two lowest-energy conformations of 2,3-dimethylbutane?
the energy of one gauche interaction
the energy of two gauche interactions
the energy of two H ↔ CH3 eclipsing interactions
the energy of three H ↔ CH3 eclipsing interactions
the energy of two CH3 ↔ CH3 eclipsing interactions

95. Learning Check 16 kJ/mol 20 kJ/mol 26 kJ/mol 31 kJ/mol 37 kJ/mol
The highest energy conformation of ethane has 12 kJ/mol of strain. The two highest conformations of butane have 16 and 19 kJ/mol of strain, respectively. How much strain does the highest energy conformation of 2,3-dimethylbutane have?
16 kJ/mol
20 kJ/mol
26 kJ/mol
31 kJ/mol
37 kJ/mol

96. Solution 16 kJ/mol 20 kJ/mol 26 kJ/mol 31 kJ/mol 37 kJ/mol
The highest energy conformation of ethane has 12 kJ/mol of strain. The two highest conformations of butane have 16 and 19 kJ/mol of strain, respectively. How much strain does the highest energy conformation of 2,3-dimethylbutane have?
16 kJ/mol
20 kJ/mol
26 kJ/mol
31 kJ/mol
37 kJ/mol