1. ORGANIC CHEMISTRY 171
Section 201

2. Alkanes
and
Cycloalkanes
Chapter 2

3. Structure Hydrocarbon: a compound composed only of carbon and hydrogen
Saturated hydrocarbon: a hydrocarbon containing only single bonds
Alkane: a saturated hydrocarbon whose carbons are arranged in an open chain
Aliphatic hydrocarbon: another name for an alkane

4. Hydrocarbons

5. Functional Groups
Functional group: An atom or group of atoms within a molecule that shows a characteristic set of physical and chemical properties.
Functional groups are important for three reasons:
1. Allow us to divide compounds into classes.
2. Each group undergoes characteristic chemical reactions.
3. Provide the basis for naming compounds.

6. Organic Molecules and Functional Groups
Functional Groups: Hydrocarbons
Hydrocarbons are compounds made up of only the elements carbon and hydrogen. They may be aliphatic or aromatic.

7. Organic Molecules and Functional Groups
Functional Groups: Heteroatoms

8. Functional Groups: Carbonyl groups

9. Alcohols
Contain an -OH (hydroxyl) group bonded to a tetrahedral carbon atom.
Ethanol may also be written as a condensed structural formula.

10. Alcohols
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) depending on the number of carbon atoms bonded to the carbon bearing the -OH group.

11. Alcohols
There are two alcohols with molecular formula C3H8O

12. Amines
Contain an amino group; an sp3-hybridized nitrogen bonded to one, two, or three carbon atoms.
An amine may by 1°, 2°, or 3°.

13. Aldehydes and Ketones
Contain a carbonyl (C=O) group.

14. Carboxylic Acids
Contain a carboxyl (-COOH) group.

15. Carboxylic Esters
Ester: A derivative of a carboxylic acid in which the carboxyl hydrogen is replaced by a carbon group.

16. Carboxylic Amide
Carboxylic amide, commonly referred to as an amide: A derivative of a carboxylic acid in which the -OH of the -COOH group is replaced by an amine.
The six atoms of the amide functional group lie in a plane with bond angles of approximately 120°.

17. Alkanes

18. Structure Shape sp3 hybridization tetrahedral about carbon
all bond angles are approximately 109.5°
sp3 hybridization

19. Drawing Alkanes Line-angle formulas
an abbreviated way to draw structural formulas
each vertex and line ending represents a carbon

20. Constitutional Isomerism
Constitutional isomers: compounds with the same molecular formula but a different connectivity of their atoms
example: C4H10

21. Constitutional Isomerism
do these formulas represent constitutional isomers?
find the longest carbon chain
number each chain from the end nearest the first branch
compare chain lengths as well the identity and location of branches

22. Constitutional Isomerism
World population
is about
6,000,000,000

23. Nomenclature - IUPAC Suffix -ane specifies an alkane
Prefix tells the number of carbon atoms

24. Nomenclature - IUPAC Parent name: the longest carbon chain
Substituent: a group bonded to the parent chain
alkyl group: a substituent derived by removal of a hydrogen from an alkane; given the symbol R-

25. Nomenclature - IUPAC
1.The name of a saturated hydrocarbon with an unbranched chain consists of a prefix and suffix
2. The parent chain is the longest chain of carbon atoms
3. Each substituent is given a name and a number
4. If there is one substituent, number the chain from the end that gives it the lower number

26. Nomenclature - IUPAC
5. If there are two or more identical substituents, number the chain from the end that gives the lower number to the substituent encountered first
indicate the number of times the substituent appears by a prefix di-, tri-, tetra-, etc.
use commas to separate position numbers

27. Nomenclature - IUPAC
6. If there are two or more different substituents,
list them in alphabetical order
number from the end of the chain that gives the substituent encountered first the lower number

28. Nomenclature - IUPAC
7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization
alphabetize the names of substituents first and then insert these prefixes

29. Nomenclature - IUPAC
Alkyl groups

30. Nomenclature - Common
The number of carbons in the alkane determines the name
all alkanes with four carbons are butanes, those with five carbons are pentanes, etc.
iso- indicates the chain terminates in -CH(CH3)2; neo- that it terminates in -C(CH3)3

31. Classification of C & H
Primary (1°) C: a carbon bonded to one other carbon
1° H: a hydrogen bonded to a 1° carbon
Secondary (2°) C: a carbon bonded to two other carbons
2° H: a hydrogen bonded to a 2° carbon
Tertiary (3°) C: a carbon bonded to three other carbons
3° H: a hydrogen bonded to a 3° carbon
Quaternary (4°) C: a carbon bonded to four other carbons

32. Cycloalkanes General formula CnH2n Structure and nomenclature
five- and six-membered rings are the most common
Structure and nomenclature
to name, prefix the name of the corresponding open-chain alkane with cyclo-, and name each substituent on the ring
if only one substituent, no need to give it a number
if two substituents, number from the substituent of lower alphabetical order
if three or more substituents, number to give them the lowest set of numbers and then list substituents in alphabetical order

33. Cycloalkanes Line-angle drawings each line represents a C-C bond
each vertex and line ending represents a C

34. Cycloalkanes
Example: name these cycloalkanes

35. IUPAC - General prefix-infix-suffix
prefix tells the number of carbon atoms in the parent
infix tells the nature of the carbon-carbon bonds
suffix tells the class of compound
Nature of Carbon-Carbon
Bonds in the Parent Chain
Suffix
Class
Infix -e
hydrocarbon
-an-
all single bonds
-ol
alcohol
-en-
one or more double bonds
-al
aldehyde
-yn-
one or more triple bonds
-amine
amine
-one
ketone
-oic acid
carboxylic acid

36. IUPAC - General prop-en-e = propene eth-an-ol = ethanol
but-an-one = butanone
but-an-al = butanal
pent-an-oic acid = pentanoic acid
cyclohex-an-ol = cyclohexanol
eth-yn-e = ethyne
eth-an-amine = ethanamine

37. Conformations
Conformation: any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond
Newman projection: a way to view a molecule by looking along a carbon-carbon single bond

38. Conformations
Staggered conformation: a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from the atoms or groups on an adjacent carbon

39. Conformations
Eclipsed conformation: a conformation about a carbon-carbon single bond in which the atoms or groups of atoms on one carbon are as close as possible to the atoms or groups of atoms on an adjacent carbon

40. Conformations Torsional strain also called eclipsed interaction strain
strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation
the torsional strain between eclipsed and staggered ethane is approximately 12.6 kJ (3.0 kcal)/mol

41. Conformations
Dihedral angle (Q): the angle created by two intersecting planes

42. Conformations Steric strain (nonbonded interaction strain):
the strain that arises when atoms separated by four or more bonds are forced closer to each other than their atomic (contact) radii will allow
Angle strain:
strain that arises when a bond angle is either compressed or expanded compared to its optimal value

43. Cyclopropane
angle strain: the C-C-C bond angles are compressed from 109.5° to 60°
torsional strain: there are 6 sets of eclipsed hydrogen interactions
strain energy is about 116 kJ (27.7 kcal)/mol

44. Cyclohexane
Chair conformation: the most stable puckered conformation of a cyclohexane ring
all bond C-C-C bond angles are 110.9°
all bonds on adjacent carbons are staggered

45. Cyclohexane
In a chair conformation, six H are equatorial and six are axial

46. Cyclohexane
For cyclohexane, there are two equivalent chair conformations
all C-H bonds equatorial in one chair are axial in the alternative chair, and vice versa

47. Cyclohexane
Boat conformation: a puckered conformation of a cyclohexane ring in which carbons 1 and 4 are bent toward each other
there are four sets of eclipsed C-H interactions and one flagpole interaction
a boat conformation is less stable than a chair conformation by 27 kJ (6.5 kcal)/mol

48. Cyclohexane Twist-boat conformation
approximately 41.8 kJ (5.5 kcal)/mol less stable than a chair conformation
approximately 6.3 kJ (1.5 kcal)/mol more stable than a boat conformation

49. Methylcyclohexane
Equatorial and axial methyl conformations

50. Cis,Trans Isomerism Stereoisomers: compounds that have
the same molecular formula
the same connectivity
a different orientation of their atoms in space
Cis,trans isomers
stereoisomers that are the result of the presence of either a ring (this chapter) or a carbon-carbon double bond (Chapter 5)

51. Cis,Trans Isomers
1,2-Dimethylcyclopentane

52. Cis,Trans Isomerism
1,4-Dimethylcyclohexane

53. Cis,Trans Isomerism trans-1,4-Dimethylcyclohexane
the diequatorial-methyl chair conformation is more stable by approximately 2 x (7.28) = kJ/mol

54. Cis,Trans Isomerism
cis-1,4-Dimethylcyclohexane

55. Physical Properties
Low-molecular-weight alkanes (methane....butane) are gases at room temperature
Higher molecular-weight alkanes (pentane, decane, gasoline, kerosene) are liquids at room temperature
High-molecular-weight alkanes (paraffin wax) are semisolids or solids at room temperature

56. Physical Properties
Constitutional isomers have different physical properties

57. Preparation and Reactions of Alkanes

58. Preparation of Alkanes via Reduction
1) Hydrogenation of Alkenes
Hydrogenation of Alkynes

59. Reduction of an alkyl halide
a) hydrolysis of a Grignard reagent (two steps)
i) R—X Mg  RMgX (Grignard reagent)
ii) RMgX H2O  RH Mg(OH)X
SB SA WA WB
CH3CH2CH2-Br Mg  CH3CH2CH2-MgBr
n-propyl bromide n-propyl magnesium bromide
CH3CH2CH2-MgBr H2O  CH3CH2CH Mg(OH)Br
propane

60. CH3CH-Br + Mg  CH3CH-MgBr
isopropyl bromide isopropyl magnesium bromide
CH3
CH3CH-MgBr H2O  CH3CH2CH3
propane
CH3CH2CH2-MgBr D2O  CH3CH2CH2D
heavy water
CH CH3
CH3CH-MgBr D2O  CH3CHD

61. with an active metal and an acid R—X + metal/acid  RH
active metals = Sn, Zn, Fe, etc.
acid = HCl, etc. (H+)
CH3CH2CHCH Sn/HCl  CH3CH2CH2CH3 + Cl
sec-butyl chloride n-butane
CH CH3
CH3CCH Zn/H+  CH3CHCH ZnBr2 Br
tert-butyl bromide isobutane
SnCl2

62. Reactions of alkanes: alkane + H2SO4  no reaction (NR)
alkane NaOH  NR
alkane Na  NR
alkane KMnO4  NR
alkane H2,Ni  NR
alkane Br2  NR
alkane H2O  NR
(Alkanes are typically non-reactive. They don’t react with acids, bases, active metals, oxidizing agents, reducing agents, halogens, etc.)

63. Alkane, reactions: Halogenation 2. Combustion (oxidation)
3. Pyrolysis (cracking)

64. Halogenation R-H + X2, heat or hv  R-X + HX
a) heat or light required for reaction.
b) X2: Cl2 > Br2  I2
c) yields mixtures 
d) H: 3o > 2o > 1o > CH4
e) bromine is more selective

65. CH3CH3 + Cl2, hv  CH3CH2-Cl + HCl
ethane ethyl chloride
CH3CH2CH Cl2, hv  CH3CH2CH2-Cl CH3CHCH3
propane n-propyl chloride Cl
isopropyl chloride %
55%
gives a mixture of both the possible
alkyl halides! 

66. CH3CH2CH2CH3 + Cl2, hv  CH3CH2CH2CH2-Cl + CH3CH2CHCH3 72% Cl
n-butane n-butyl chloride 28% +
CH3CH2CHCH % Cl
sec-butyl chloride
CH CH3
CH3CHCH Cl2, hv  CH3CHCH2-Cl %
isobutane isobutyl chloride
CH3
CH3CCH %
tert-butyl chloride

67. chlorination of propane, mechanism:
abstraction of 1o hydrogen:
Cl• CH3CH2CH3  CH3CH2CH2• HCl
or abstraction of 2o hydrogen:
Cl• CH3CH2CH3  CH3CHCH HCl •
2)CH3CH2CH2• Cl2  CH3CH2CH2Cl Cl•
or CH3CHCH Cl2  CH3CHCH Cl•
• Cl
plus terminating steps 3) Cl—Cl  2 Cl•

68. 2.Oxidation of Alkanes ( combustion )
Oxidation is the basis for their use as energy sources for heat and power
heat of combustion: heat released when one mole of a substance in its standard state is oxidized to carbon dioxide and water

69. Sources of Alkanes Natural gas Petroleum Coal 90-95% methane
gases (bp below 20°C)
naphthas, including gasoline (bp °C)
kerosene (bp °C)
fuel oil (bp °C)
lubricating oils (bp above 350°C)
asphalt (residue after distillation)
Coal

70. Gasoline
Octane rating: the percent 2,2,4-trimethylpentane (isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties

71. Synthesis Gas
A mixture of carbon monoxide and hydrogen in varying proportions which depend on the means by which it is produced

72. Synthesis Gas
Synthesis gas is a feedstock for the industrial production of methanol and acetic acid
it is likely that industrial routes to other organic chemicals from coal via methanol will also be developed

73. Alkanes and Cycloalkanes
End Chapter 2