1. Essential Organic Chemistry
Paula Yurkanis Bruice
Chapter 3
An Introduction to Organic Compounds: Nomenclature, Physical Properties, and Representation of Structure

2. Alkanes Saturated hydrocarbons (Aliphatic)
Hydrocarbons – Contain only C and H atoms.
Saturated – Only single bonds.
Aliphatic – “Fat” like.
Straight-chain and branched-chain alkanes
Can be acyclic (no rings) or cyclic (cycloalkanes).

3. Alkanes

4. Alkanes

5. Isomerism
Consider C4H10
These structures are constitutional isomers

6. Isomerism
Consider C5H12
These structures are constitutional isomers

7. Isomerism
Consider C6H14
These structures are constitutional isomers

8. Isomerism
Isomerism – The phenomenon whereby certain chemical compounds have structures that are different although the compounds possess the same elemental composition.
Isomers – Two or more chemical substances having the same elementary composition and molecular weight but differing in structure.

9. 3.1 Nomenclature of Alkyl Substituents
Names and Formulas of Alkyl Groups:
Formula
Name
CH3-
methyl
CH3CH2CH2CH2-
butyl
CH3CH2-
ethyl
(CH3)2CHCH2-
isobutyl
CH3CH2CH2-
propyl
CH3CH2CH(CH3)-
sec-butyl
(CH3)2CH-
isopropyl
(CH3)3C-
tert-butyl

10. Nonsystematic names; Common names

12. Primary (1o) carbon – a carbon that is bonded to only one other carbon.
Secondary (2o) carbon– a carbon that is bonded to two other carbons.
Tertiary (3o) carbon– a carbon that is bonded to three other carbons.

13. Nonsystematic names; Common names
Figure: UN
Title:
Iso-alkyl groups
Caption:
Whenever the iso- prefix is used, the iso- structural unit will be at one end of the structure and the group replacing the hydrogen is at the other end.
Notes:

14. Names of Some Alkyl Groups
Figure: UN.T2
Title:
Table 3.2 Names of some alkyl groups
Caption:
The condensed structures of various alkyl groups for the first 6 alkanes.
Notes:
The condensed structures of various alkyl groups for methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, isohexyl.

17. 3.2 IUPAC Nomenclature of Alkanes
1. Determine the number of carbons in the longest continuous carbon chain as the parent hydrocarbon.
2. Number the chain so that the substituent gets the lowest possible number.
Numbers are used only for systematic names, never for common names.
A number and a word are separated by a hyphen

18. 3.2 IUPAC Nomenclature of Alkanes
3. Substituent are listed in alphabetical order.
Numbers are separated by a comma.
When the same alkyl group branch chain occurs more than once, indicate this repetition by a prefix (di, tri, tetra, and so forth).
di, tri, tetra, sec, and so on are ignored in alphabetizing.
iso and cyclo are not ignored in alphabetizing.
4. When both directions lead to the same lowest number for one of the substituents, the direction that gives the lowest possible number to one of the remaining substituents is chosen.

19. 3.2 IUPAC Nomenclature of Alkanes
5. If the same substituent numbers are obtained in both directions, the first group cited receives the lower number.
6. If a compound has two or more chains of the same length, the parent hydrocarbon is the chain with the greatest number of substituents.

20. Examples

21. Examples

22. Examples
Note: Number the chain so that the substituents get the lowest possible numbers.

23. Examples
Caution: Be careful to choose the longest chain as the parent alkane.

24. Examples
Note: Substituents are listed in alphabetical order.

25. Draw the Compounds
3-ethylpentane
2,2,4-trimethylpentane

28. 3.3 IUPAC Nomenclature of Cycloalkanes
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

29. IUPAC Nomenclature of Cycloalkanes
In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent hydrocarbon.
There is no need to number the position of a single substituent on a ring.
If the ring has two different substituents, they are cited in alphabetical order and the number 1 position is given to the substituent cited first.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

30. Cycloalkanes
Cyclopropane
Methylcyclohexane

31. Cycloalkanes
1-Cyclobutylhexane or
Hexylcyclobutane

32. Cycloalkanes
1-Ethyl-2-methylcyclohexane

33. Name the Following Compounds
Methylcyclopropane
1,1-Dimethylcyclohexane
1,2-Dimethylcyclopentane
3-Cyclopropylpentane

34. Figure: UN
Title:
Skeletal structures of alkanes
Caption:
Skeletal structures of noncyclic alkanes.
Notes:
These are line drawings that are generally used when representing alkanes. It is understood that each vertex is a carbon atom and that there are the appropriate number of hydrogens attached to each.

38. 3.4 IUPAC Nomenclature of Alkyl Halides
Common name: alkyl group + halogen, with the “ine” ending replaced by “ide” (fluoride, chloride, bromide, iodide)
IUPAC name: substituted alkanes, with the substituent prefix for the halogens end with “O” (fluoro, chloro, bromo, iodo)
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

39. IUPAC Nomenclature of Alkyl Halides
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

41. 3.5 Classification of Alkyl Halides, Alcohols, and Amines
The number of alkyl groups attached to the carbon to which the halogen is bonded determines whether an alkyl halide is primary, secondary, or tertiary.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

42. Classification of Alkyl Halides, Alcohols, and Amines
The number of alkyl groups attached to the carbon to which the OH group is attached determines whether an alcohol is primary, secondary, or tertiary.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

43. Classification of Alkyl Halides, Alcohols, and Amines
The number of alkyl groups attached to the nitrogen determines whether an amine is primary, secondary, or tertiary.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

45. 3.6 Structures of Alkyl Halides, Alcohols, Ethers, and Amines
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

46. Structures of Alkyl Halides, Alcohols, Ethers, and Amines
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

47. Structures of Alkyl Halides, Alcohols, Ethers, and Amines
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

48. Structures of Alkyl Halides, Alcohols, Ethers, and Amines
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

50. 3.7 Physical Properties of Alkanes, Alkyl Halides, Alcohols, Ethers, and Amines
Boiling Points (bp) – the temperature at which the liquid form of the compound become a gas (vaporizes).
Induced-dipole-induced-dipole interactions
van der Waals forces – in order for an alkane to boil, the van der Waals forces must be overcome.
The van der Waals forces that hold
alkane molecules together depends
on the area of contact between the
molecules.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

51. Boiling Points of Alkanes
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.
Boiling points increase with increasing molecular weight within a homologous series of alkanes.

52. Boiling Points of Alkanes
Branching decreases the area of contact between molecules.
If two alkanes have the same molecular weight, the more highly branched alkane will have a lower boiling point.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

53. Boiling Points of Ethers, Alcohols, and Amines
Boiling points increase with increasing molecular weight within a homologous series.
Ethers generally have higher boiling points than alkanes of comparable molecular weight because both van der Waals forces and dipole-dipole interactions must be overcome.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

54. Boiling Points of Ethers, Alcohols, and Amines
3. Alcohols have much higher boiling points than alkanes or ethers of comparable molecular weight because, in addition to van der Waals forces and dipole-dipole interactions, hydrogen bonds have to be broken as well.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

55. Boiling Points of Ethers, Alcohols, and Amines
4. Primary and secondary amines also form hydrogen bonds, so these amines have higher boiling points than alkanes with similar molecular weights.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

58. Boiling Points of Alkyl Halides
5. Both van der Waals forces and dipole-dipole-interactions must be overcome for alkyl halides to boil.
6. As the halogen atom increases in size, the size of its electron cloud increases, and the larger the electron cloud, the stronger are the van der Waals interactions.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

60. Melting Points of Alkanes
Melting Points (mp) – the temperature at which a solid is converted into a liquid.
The increase in mp is less regular than that in bp because packing influences the mp of a compound.
Packing – a property that determines how well the individual molecules in a solid fit together in a crystal lattice.
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

61. Melting Points of Alkanes
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.
Melting points increase with increasing molecular weight within a homologous series of alkanes.

62. Melting Points of Alkanes
Figure: UN
Title:
Structures of cycloalkanes
Caption:
Structures of the cycloalkanes cyclopropane, cyclobutane, cyclopentane, cyclohexane.
Notes:
Note the molecular formula for a cycloalkane is CnH2n.

63. Solubility of Alkanes Solubility – “Like dissolves like”
Alkanes are nonpolar, hydrophobic
They are soluble in nonpolar solvents and insoluble in water.

66. 3.8 Conformations of Alkanes: Rotation About Carbon-Carbon Bonds
The different spatial arrangements of the atoms that result from rotation about a single bond are called “conformations”.
A specific conformation is called a conformer.

67. Conformations of Alkanes
When rotation occurs about the carbon-carbon bond of ethane, two extreme conformations can result- a staggered conformations and an eclipsed conformation.
In a Newman projection, you are looking down the length of a particular C-C bond.

68. Conformations of Alkanes
Ethane
Staggered conformation
Newman projection: =

69. Conformations of Alkanes
Ethane
Eclipsed conformation
Newman projection: =
~3 kcal/mole higher in energy than staggered conformation

70. Conformations of Alkanes
The electrons in a C-H bond will repel the electrons in another C-H bond if the bonds get too close to each other. This is called “torsional strain”.
Staggered conformer: the most stable; at energy minima
Eclipsed conformer: the least stable ; at energy maxima

71. Conformations of Alkanes
Steric strain is the strain (extra energy) put on a molecule when atoms or groups are too close to one another.

73. 3.9 Cycloalkanes: Ring Strain
The deviation of the bond angle from the ideal bond angle causes strain called angle strain.
Cyclopropane: 60o ; Cyclobutane: 90o.
Cyclobutane: a bent molecule, not planar- to reduce torsional strain!

74. 3.10 Conformations of Cyclohexane
“Chair” conformation

75. Conformations of Cyclohexane
“Chair” conformation
Equatorial hydrogens

76. Figure: UN
Title:
Conformation of Cyclohexane
Caption:
The chair conformation of cyclohexane showing the positions of the equatorial bonds.
Notes:
The axial bonds are the other bonds shown but not highlighted.

77. Conformations of Cyclohexane
“Chair” conformation
Axial hydrogens

78. Figure: UN
Title:
Conformation of Cyclohexane
Caption:
The chair conformation of cyclohexane showing the positions of the axial bonds.
Notes:

79. Figure: 03-06
Title:
Chair Conformation of Cyclohexane
Caption:
The skeletal structure, Newman projection, and ball-and-stick models of the chair conformation of cyclohexane.
Notes:
All the bonds are staggered in these models.

80. Figure: UN
Title:
Chair Conformation of Cyclohexane
Caption:
The chair conformation of cyclohexane showing the positions of all the axial and equatorial bonds.
Notes:
Remember that the lower bonds are in front and the upper bonds are in back since this molecule is shown on edge.

82. Figure: 03-07
Title:
Ring Flip of Cyclohexane
Caption:
The bonds that are axial in one chair conformer are equatorial in the other chair conformer. The bonds that are equatorial in one chair conformer are axial in the other chair conformer.
Notes:
This ring flip occurs very rapidly at room temperature.

83. Conformations of Cyclohexane
“Boat” conformation

84. Conformations of Cyclohexane
“Boat” conformation
Steric interactions

85. Conformations of Cyclohexane
“Boat” conformation
Eclipsing

86. Conformations of Cyclohexane
“Twist-boat” conformation
“Half-chair” conformation

87. Conformations of Cyclohexane
Figure: 03-08
Title:
Conformations of Cyclohexane
Caption:
Conformations of cyclohexane (and their relative energies) during a ring flip.
Notes:
The chair conformations are the most stable. The twist-boat is the next most stable conformation.

88. 3.11 Conformations of Monosubstituted Cyclohexanes
Methylcyclohexane

89. Conformations of Monosubstituted Cyclohexanes
Methylcyclohexane C H 3
steric interactions
more stable

90. Conformations of Monosubstituted Cyclohexanes
tert-Butylcyclohexane
severe steric interactions
much more stable

92. 3.12 Conformations of Disubstituted Cyclohexanes
cis-1,3-Dimethylcyclohexane
severe steric interactions
much more stable

93. Figure: UN
Title:
Geometric Isomers of 1,4-dimethylcyclohexane
Caption:
These are the cis and trans isomers of 1,4-dimethylcyclohexane. When the methyl groups are cis, one is in the axial position and the other is in the equatorial position. When they are trans, both are in the equatorial position.
Notes:
When the methyl groups are cis, one is in the axial position and the other is in the equatorial position. When they are trans, both are in the equatorial position.

94. Figure: UN
Title:
Ring Flip of cis-1,4-Dimethylcyclohexane
Caption:
When the ring flips between the two chair conformations the methyl group that was in the equatorial position becomes axial and the axial becomes equatorial.
Notes:
Both conformers are equally stable since at least one of the substituents is equatorial.

95. Figure: UN
Title:
Ring Flip of trans-1,4-Dimethylcyclohexane
Caption:
When the ring flips between the two chair conformations the methyl groups that were in the equatorial positions become axial.
Notes:
In this case the first conformation is the more stable conformation since both methyl groups are in the equatorial position.

100. 3.13 Conformations of Fused Rings
Figure: UN
Title:
Fused Rings
Caption:
Trans-fused rings are more stable than are cis-fused rings since all substituents are in the equatorial position.
Notes:
In the trans-fused ring both substituents are in the equatorial position, which is more stable.

101. Figure: UN
Title:
Structure of Cholesterol
Caption:
Structure of cholesterol.
Notes:
Cholesterol is the important component of cell membranes.