1. Alkanes
and
Cycloalkanes
Unit 4

2. 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

3. Hydrocarbons H - C y d r o c a b n s A l k e O i g m u t p z E x N h B

4. Structure Shape tetrahedral about carbon
all bond angles are approximately 109.5°

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

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

7. 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

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

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

10. 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-

11. 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

12. 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

13. 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

14. 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

15. Nomenclature - IUPAC
Alkyl groups

16. 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

17. 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

18. Cycloalkanes General formula CnH2n Structure and nomenclature
five- and six-membered rings are the most common and most stable
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

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

20. Cycloalkanes
Example: name these cycloalkanes

21. Bicycloalkanes
Bicycloalkane: an alkane that contains two rings that share two carbons
Bicyclo[4.4.0]decane
(Decalin)
Bicyclo[4.3.0]nonane
(Hydrindane)
Bicyclo[2.2.1]heptane
(Norbornane)

22. Bicycloalkanes Nomenclature
parent is the alkane of the same number of carbons as are in the rings
number from a bridgehead, along longest bridge back to the bridgehead, then along the next longest bridge, etc.
show the lengths of bridges in brackets, from longest to shortest

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. Cyclobutane
puckering from planar cyclobutane reduces torsional strain but increases angle strain
the conformation of minimum energy is a puckered “butterfly” conformation
strain energy is about 110 kJ (26.3 kcal)/mol

30. Cyclopentane
puckering from planar cyclopentane reduces torsional strain, but increases angle stain
the conformation of minimum energy is a puckered “envelope” conformation
strain energy is about 42 kJ (6.5 kcal)/mol

31. 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

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

33. 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

34. 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

35. 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 or a carbon-carbon double bond

36. Isomers
relationships among isomers

37. Cis,Trans Isomers
1,2-Dimethylcyclopentane

38. Cis,Trans Isomerism
1,4-Dimethylcyclohexane

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

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

41. Cis,Trans Isomerism
The decalins

42. Bicycloalkanes
Norbornane drawn from three different perspectives

43. Bicycloalkanes
Adamantane

44. Physical Properties Intermolecular forces of attraction (example)
ion-ion (Na+ and Cl- in NaCl)
ion-dipole (Na+ and Cl- solvated in aqueous solution)
dipole-dipole and hydrogen bonding
dispersion forces (very weak electrostatic attraction between temporary dipoles)

45. 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

46. Physical Properties
Constitutional isomers have different physical properties

47. Oxidation of Alkanes
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

48. Heat of Combustion
Heat of combustion for constitutional isomers

49. Heats of Combustion For constitutional isomers [kJ (kcal)/mol]
( )
( )
(1304.6)
(1303.0) 8 C O 2 + 9 H 2 O

50. 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

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