1. An Introduction to Organic Chemistry: The Saturated Hydrocarbons
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Chapter 10
An Introduction to Organic Chemistry:
The Saturated Hydrocarbons
Denniston Topping Caret
5th Edition

2. 10.1 The Chemistry of Carbon
Why are there so many organic compounds?
Carbon forms stable, covalent bonds with other carbon atoms
Consider three allotropic forms of elemental carbon
Graphite in planar layers
Diamond is a three-dimensional network
Buckminsterfullerene is 60 C in a roughly spherical shape

3. Why are there so many organic compounds?
Carbon atoms form stable bonds with other elements, such as:
Oxygen
Nitrogen
Sulfur
Halogen
Presence of these other elements confers many new physical and chemical properties on an organic compound
10.1 The Chemistry of Carbon

4. Why are there so many organic compounds?
Carbon atoms form double or triple bonds with:
Other carbon atoms (double & triple)
Oxygen (double only)
Nitrogen (double & triple)
These combinations act to produce a variety of organic molecules with very different properties
10.1 The Chemistry of Carbon

5. Why are there so many organic compounds?
Carbon atoms can be arranged with these other atoms; is nearly limitless
Branched chains
Ring structures
Linear chains
Two organic compounds may even have the same number and kinds of atoms but completely different structures and thus, different properties
These are called isomers
10.1 The Chemistry of Carbon

6. 10.1 The Chemistry of Carbon
Isomers
Many carbon compounds exist in the form of isomers
Isomers are compounds with the same molecular formula but different structures
An isomer example: both are C4H10 but have different structures
Butane
Methylpropane
10.1 The Chemistry of Carbon

7. 10.1 The Chemistry of Carbon
Isomers
All have the same molecular formula: C4H8
10.1 The Chemistry of Carbon

8. Important Differences Between Organic and Inorganic Compounds
Bond type
Organics have covalent bonds
Electron sharing
Inorganics usually have ionic bonds
Electron transfer
Structure
Organics
Molecules
Nonelectrolytes
Inorganics
Three-dimensional crystal structures
Often water-soluble, dissociating into ions -electrolytes
10.1 The Chemistry of Carbon

9. Important Differences Between Organic and Inorganic Compounds
Melting Point & Boiling Point
Organics have covalent bonds
Intermolecular forces broken fairly easily
Inorganics usually have ionic bonds
Ionic bonds require more energy to break
Water Solubility
Organics
Nonpolar, water insoluble
Inorganics
Water-soluble, readily dissociate
10.1 The Chemistry of Carbon

10. Comparison of Major Properties of Organic and Inorganic Compounds
10.1 The Chemistry of Carbon

11. Bonding Characteristics and Isomerism
One reason for the power of carbon is that it can form 4 covalent bonds
It appears to have only 2 available electrons
Carbon can hybridize its orbitals to move 2 electrons out of it 2s orbital
10.1 The Chemistry of Carbon

12. 10.1 The Chemistry of Carbon
Hybrid Orbitals
Each carbon-hydrogen bond in methane arises from an overlap of a C(sp3) and an H(1s) orbital
4 equivalent sp3 orbitals point toward the corners of a regular tetrahedron
The 4 sp3 hybrid orbitals of carbon combine with the 1s orbitals on 4 H to produce methane – CH4
10.1 The Chemistry of Carbon

13. Families of Organic Compounds
Hydrocarbons contain only carbon
and hydrogen
They are nonpolar molecules
Not soluble in water
Are soluble in typical nonpolar organic solvents
Toluene
Pentane
10.1 The Chemistry of Carbon

14. Families of Organic Compounds
Hydrocarbons are constructed of chains or rings of carbon atoms with sufficient hydrogen atoms to fulfill carbon’s need for four bonds
Substituted hydrocarbon is one in which one or more hydrogen atoms is replaced by another atom or group of atoms
10.1 The Chemistry of Carbon

15. Division of the Family of Hydrocarbons
10.1 The Chemistry of Carbon

16. Hydrocarbon Saturation
Alkanes are compounds that contain only carbon-carbon and carbon-hydrogen single bonds
A saturated hydrocarbon has no double or triple bonds
Alkenes and alkynes are unsaturated because they contain at least one carbon to carbon double or triple bond
10.1 The Chemistry of Carbon

17. Cyclic Structure of Hydrocarbons
Some hydrocarbons are cyclic
Form a closed ring
Aromatic hydrocarbons contain a benzene ring or related structure
10.1 The Chemistry of Carbon

18. Common Functional Groups
10.1 The Chemistry of Carbon

19. 10.2 Alkanes The general formula for a chain alkane is CnH2n+2
In this formula n = the number of carbon atoms in the molecule
Alkanes are saturated hydrocarbons
Contain only carbon and hydrogen
Bonds are carbon-hydrogen and carbon-carbon single bonds

20. Formulas Used in Organic Chemistry
Molecular formula - lists kind and number of each type of atom in a molecule, no bonding pattern
Structural formula - shows each atom and bond in a molecule
Condensed formula - shows all the atoms in a molecule in sequential order indicating which atoms are bonded to which
Line formula - assume a carbon atom at any location where lines intersect
Assume a carbon at the end of any line
Each carbon in the structure is bonded to the correct number of hydrogen atoms
10.2 Alkanes

21. The Tetrahedral Carbon Atom
10.2 Alkanes
Lewis dot structure
The tetrahedral shape around the carbon atom
The tetrahedral carbon drawn with dashes and wedges
The stick drawing of the tetrahedral carbon atom
Ball and stick model of methane

22. Drawing Methane and Ethane
10.2 Alkanes
Staggered form of ethane

23. Comparison of Ethane and Butane Structures
10.2 Alkanes

24. Names and Formulas of the First Ten Straight-Chain Alkanes

25. 10.2 Alkanes Structural Isomers Butane Bp –0.4 oC Mp –139 oC Isobutane
Constitutional/Structural Isomers differ in how atoms are connected
Two isomers of butane have different physical properties
The carbon atoms are connected in different patterns
10.2 Alkanes
Butane
Bp –0.4 oC
Mp –139 oC
Isobutane
Bp –12 oC
Mp –145 oC

26. Comparison of Physical Properties of Five Isomers of Hexane
Compare the basic linear structure of hexane
All other isomers have one or more carbon atoms branching from the main chain
Branched-chain forms of the molecule have a much smaller surface area
Intermolecular forces are weaker
Boiling and melting points are lower than straight chains
10.2 Alkanes

27. Physical Properties of Organic Molecules
Nonpolar
Not water soluble
Soluble in nonpolar organic solvents
Low melting points
Low boiling points
Generally less dense (lighter) than water
As length (molecular weight) increases, melting and boiling points increase as does the density
10.2 Alkanes

28. Properties of Alkanes
10.2 Alkanes

29. 10.2 Alkanes Properties of Alkanes
Most of the alkanes are hydrophobic:
water hating
Straight chain alkanes comprise a homologous series: compounds of the same functional class that differ by a –CH2- group
Nonpolar alkanes are:
Insoluble in water (a highly polar solvent)
Less dense than water and float on it
10.2 Alkanes

30. Alkyl Groups
10.2 Alkanes
An alkyl group is an alkane with one hydrogen atom removed
It is named by replacing the -ane of the alkane name with -yl
Methane becomes a methyl group

31. 10.2 Alkanes Alkyl Groups All six hydrogens on ethane are equivalent
Removing one H generates the ethyl group
All 3 structures shown at right are the same
10.2 Alkanes

32. Names and Formulas of the First Five Alkyl Groups
10.2 Alkanes

33. Alkyl Group Classification
Alkyl groups are classified according to the number of carbons attached to the carbon atom that joins the alkyl group to a molecule
All continuous chain alkyl groups are 1º
Isopropyl and sec-butyl are 2º groups
10.2 Alkanes

34. 10.2 Alkanes Iso- Alkyl Groups n-propyl isopropyl
Propane: removal of a hydrogen generates two different propyl groups depending on whether an end or center H is removed
10.2 Alkanes
n-propyl
isopropyl

35. 10.2 Alkanes Sec- Alkyl Groups n-butyl sec-butyl
n-butane gives two butyl groups depending on whether an end (1º) or interior (2º) H is removed
10.2 Alkanes
n-butyl
sec-butyl

36. Structures and Names of Some Branched-Chain Alkyl Groups
10.2 Alkanes

37. More Alkyl Group Classification
Isobutane gives two butyl groups depending on whether a 1o or 3o H is removed
10.2 Alkanes
1o C
3o C
isobutyl
t-butyl

38. Nomenclature
The IUPAC (International Union of Pure and Applied Chemistry) is responsible for chemical names
Before learning the IUPAC rules for naming alkanes, the names and structures of eight alkyl groups must be learned
These alkyl groups are historical names accepted by the IUPAC and integrated into modern nomenclature
10.2 Alkanes

39. Carbon Chain Length and Prefixes
10.2 Alkanes

40. IUPAC Names for Alkanes
The base or parent name for an alkane is determined by the longest chain of carbon atoms in the formula
The longest chain may bend and twist, it is seldom horizontal
Any carbon groups not part of the base chain are called branches or substituents
These carbon groups are also called alkyl groups
10.2 Alkanes

41. IUPAC Names for Alkanes
Rule 1 applied
Find the longest chain in each molecule
A= B=8
10.2 Alkanes

42. IUPAC Names for Alkanes
Number the carbon atoms in the chain starting from the end with the first branch
If both branches are equally from the ends, continue until a point of difference occurs
10.2 Alkanes

43. IUPAC Names for Alkanes
Number the carbon atoms correctly
Left: first branch is on carbon 3
Right: first branch is on carbon 3 (From top) not carbon 4 (if number from right)
10.2 Alkanes 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7
this branch would be on C-4
if you started at correct C-8

44. IUPAC Names for Alkanes
Write each of the branches/substituents in alphabetical order before the base/stem name (longest chain)
Halogens usually come first
Indicate the position of the branch on the main chain by prefixing its name with the carbon number to which it is attached
Separate numbers and letters with a hyphen
Separate two or more numbers with commas
10.2 Alkanes

45. IUPAC Names for Alkanes
Name : 4-ethyl-2-methylhexane

46. IUPAC Names for Alkanes
Hyphenated and number prefixes are not considered when alphabetizing groups
Name the compound below
5-sec-butyl-4-isopropylnonane
10.2 Alkanes

47. IUPAC Names for Alkanes
When a branch/substituent occurs more than once
Prefix the name with di
tri
tetra
Then list the number of the carbon branch for that substituent to the name with a separate number for each occurrence
Separate numbers with commas
e.g., 3,4-dimethyl or 4,4,6-triethyl
10.2 Alkanes

48. IUPAC Names for Alkanes
5-ethyl-2,3-dimethylheptane
ethyl>dimethyl

49. 10.2 Alkanes Practice: IUPAC Name3 4 5 6 7 8 9 10
6-ethyl-6-isobutyl-3,3-dimethyldecane

50. 10.3 Cycloalkanes
Cycloalkanes have two less hydrogens than the corresponding chain alkane
Hexane=C6H14; cyclohexane=C6H12
To name cycloalkanes, prefix cyclo- to the name of the corresponding alkane
Place substituents in alphabetical order before the base name as for alkanes
For multiple substituents, use the lowest possible set of numbers; a single substituent requires no number

51. Cycloalkane Structures
Cyclopropane
Cyclobutane
Cyclohexane
10.3 Cycloalkanes
Type of Formula: Structural Condensed Line

52. Naming a Substituted Cycloalkane
Name the two cycloalkanes shown below
Parent chain carbon ring carbon ring
cyclohexane cyclopentane
Substituent chlorine atom a methyl group
chloro methyl
Name Chlorocyclohexane Methylcyclopentane
10.3 Cycloalkanes

53. cis-trans Isomers in Cycloalkanes
Atoms of an alkane can rotate freely around the carbon-carbon single bond having an unlimited number of arrangements
Rotation around the bonds in a cyclic structure is limited by the fact that all carbons in the ring are interlocked
Formation of cis-trans isomers, geometric isomers, is a consequence of the lack of free rotation
Stereoisomers are molecules that have the same structural formulas and bonding patterns, but different arrangements of atoms in space
cis-trans isomers of cycloalkanes are stereoisomers whose substituents differ in spatial arrangement
10.3 Cycloalkanes

54. cis-trans Isomers in Cycloalkanes
Two groups may be on the same side (cis) of the imagined plane of the cycloring or they may be on the opposite side (trans)
Geometric isomers do not readily interconvert, only by breaking carbon-carbon bonds can they interconvert
10.3 Cycloalkanes

55. 10.4 Conformations of Alkanes
Conformations differ only in rotation about carbon-carbon single bonds
Two conformations of ethane and butane are shown
The first (staggered form) is more stable because it allows hydrogens to be farther apart and thus, the atoms are less crowded

56. Two Conformations of Cyclohexane
10.4 Conformations of Alkanes and Cycloalkanes
Chair form (more stable) Boat form
E=equitorial A=axial

57. 10.5 Reactions of Alkanes
Alkanes, cycloalkanes, and other hydrocarbons can be:
Oxidized (by burning) in the presence of excess molecular oxygen, in a process called combustion
Reacted with a halogen (usually chlorine or bromine) in a halogenation reaction

58. 10.5 Reactions of Alkanes Alkane Reactions
The majority of the reaction of alkanes are combustion reactions
Complete CH4 + 2O CO2 + 2H2O Complete combustion produces
Carbon dioxide and water
Incomplete 2CH4 + 3O CO + 4H2O
Incomplete combustion produces
Carbon monoxide and water
Carbon monoxide is a poison that binds irreversibly to red blood cells
10.5 Reactions of Alkanes

59. 10.5 Reactions of Alkanes Halogenation
Halogenation is a type of substitution reaction, a reaction that results in a replacement of one group for another
Products of this reaction are:
Alkyl halide or haloalkane
Hydrogen halide
This reaction is important in converting unreactive alkanes into many starting materials for other products
Halogenation of alkanes ONLY occurs in the presence of heat and/or light (UV)
10.5 Reactions of Alkanes

60. 10.5 Reactions of Alkanes Petroleum Processing Fraction
Boiling Pt Range ºC
Carbon size
Typical uses
Gas
C1-C4
Heating, cooking
Gasoline
30-200
C5-C12
Motor fuel
Kerosene
C12-C16
Fuel for stoves, diesel and jet engines
Heating oil
Up to 375
C15-C18
Furnace oil
Lubricating oil
350 and up
C16-C20
Lubrication, mineral oil
Greases
Semisolid
C18-up
Lubrication, petroleum jelly
Paraffin (wax)
Melts at 52-57
C20-up
Candles, toiletries
Pitch / tar
Residue in boiler
High
Roofing, asphalt paving
10.5 Reactions of Alkanes