1. Chapter 25 “Hydrocarbon Compounds”
Chemistry
Golden Valley High School
Stephen L. Cotton

2. Section 25.1 Hydrocarbons
OBJECTIVES:
Describe the relationship between number of valence electrons and bonding in carbon.

3. Define and describe alkanes.
Section 25.1 Hydrocarbons
OBJECTIVES:
Define and describe alkanes.

4. Relate the polarity of hydrocarbons to their solubility.
Section 25.1 Hydrocarbons
OBJECTIVES:
Relate the polarity of hydrocarbons to their solubility.

5. Organic Chemistry and Hydrocarbons
Organic originally meant chemicals that came from organisms
1828 German chemist Friedrich Wohler synthesized urea in a lab
Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

6. Friedrich Wohler
1800 – 1882
Used inorganic substances to synthesize urea, a carbon compound found in urine.
This re-defined organic chemistry.

7. Organic Chemistry and Hydrocarbons
Over a million organic compounds, with a dazzling array of properties
Why so many? Carbon’s unique bonding ability!
Let’s start with the simplest of the organic compounds: Hydrocarbons

8. Organic Chemistry and Hydrocarbons
Hydrocarbons contain only two elements: 1) hydrogen, & 2) carbon
simplest hydrocarbons called “alkanes”, which contain only carbon to carbon single covalent bonds (CnH2n+2)
methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas

9. Organic Chemistry and Hydrocarbons
Carbon has 4 valence electrons, thus forms 4 covalent bonds
not only with other elements, but also forms bonds WITH ITSELF (nonpolar)
Ethane (C2H6) is the simplest alkane with a carbon to carbon bond

10. Straight-Chain Alkanes
Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain -meaning one linked to the next (not always straight)
C-C-C C-C-C-C etc.
Names of alkanes always will always end with -ane

11. Straight-Chain Alkanes
Combined with the -ane ending is a prefix for the number of carbons
Table 25.1, page 745
Homologous series- a group of compounds that have a constant increment of change
In alkanes, it is: -CH2- (methylene)

12. Straight-Chain Alkanes
Many alkanes used for fuels: methane, propane, butane, octane
As the number of carbons increases, so does the boiling and melting pt.
The first 4 are gases; #5-15 are liquids; higher alkanes are solids

13. Naming Straight-Chain Alkanes
Names recommended by IUPAC - the International Union of Pure and Applied Chemistry
end with –ane; the root part of the name indicates the # of carbons
We sometimes still rely on common names, some of which are well-known

14. Naming Straight-Chain Alkanes
IUPAC names may be long and cumbersome
Common names may be easier or more familiar, but usually do not describe the chemical structure!
Methane is natural gas or swamp gas

15. Branched-Chain Alkanes
Branched-chain means that other elements besides hydrogen may be attached to the carbon
halogens, oxygen, nitrogen, sulfur, and even other carbons
any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branched part

16. Branched-Chain Alkanes
A hydrocarbon substituent is called an alkyl group or sometimes radicals
use the same prefixes to indicate the number of carbons, but -ane ending is now -yl such as: methyl, ethyl, propyl, etc.
Gives much more variety to the organic compounds

17. Branched-Chain Alkanes
Rules for naming – go from right to left - page 748
1. Longest C-C chain is parent
2. Number so branches have lowest #
3. Give position number to branch
4. Prefix (di, tri) more than one branch
5. Alphabetize branches (not prefix)
6. Use proper punctuation ( - and , )

18. - Page 699

19. Branched-Chain Alkanes
From the name, draw the structure, in a right-to-left manner:
1. Find the parent, with the -ane
2. Number carbons on parent
3. Identify substituent groups (give lowest number); attach
4. Add remaining hydrogens

20. - Page 700

21. Properties of Alkanes Draw 3-ethylpentane Draw 2,3,4-trimethylhexane
Since the electrons are shared equally, the molecule is nonpolar
thus, not attracted to water
oil (a hydrocarbon) not soluble in H2O
“like dissolves like”

22. Quiz Draw. 2,3 diethyl pentane 3,3, 4 tri-methyl octane
2,3 ethyl, methyl hexane
Name
C C
C-C-C-C-C-C

23. Section 25.2 Unsaturated Hydrocarbons
OBJECTIVES:
Describe the difference between unsaturated and saturated hydrocarbons.

24. Section 25.2 Unsaturated Hydrocarbons
OBJECTIVES:
Distinguish the structures of alkenes and alkynes.

25. Alkenes Multiple bonds can also exist between the carbon atoms
Hydrocarbons containing carbon to carbon double bonds are called alkenes (CnH2n) C=C C-C=C
Called “unsaturated” if they contain double or triple bonds

26. Naming Alkenes Find longest parent that has the double bond in it
New ending: -ene
Number the chain, so that the double bond gets the lower number
Name and number the substituents
Samples on page 702

27. Alkynes
Hydrocarbons containing carbon to carbon triple bonds called alkynes
(CnH2n-2) C C-
Alkynes are not plentiful in nature
Simplest is ethyne- common name acetylene (fuel for torches)
Table 22.3, p. 703 for boiling pt.

28. Explain why structural isomers have different properties.
Section 25.3 Isomers
OBJECTIVES:
Explain why structural isomers have different properties.

29. Describe the conditions under which geometric isomers are possible.
Section 25.3 Isomers
OBJECTIVES:
Describe the conditions under which geometric isomers are possible.

30. Identify optical isomers.
Section 25.3 Isomers
OBJECTIVES:
Identify optical isomers.

31. Structural Isomers
Compounds that have the same molecular formula, but different molecular structures, are called structural isomers
Butane and 2-methylpropane (make by breaking Carbon off the end, and making a branch in the middle)
Also have different properties, such as b.p., m.p., and reactivity

32. Structural Isomers of Butane, C4H10

33. Stereoisomers
Don’t forget that these structures are really 3-dimensional
stereoisomers- molecules of the same molecular structure that differ only in the arrangement of the atoms in space. Two types are a) geometric and b) optical

34. Geometric Isomers
There is a lack of rotation around a carbon to carbon multiple bond
has an important structural implication
Two possible arrangements:
1. trans configuration - substituted groups on opposite sides of double bond
2. cis configuration - same side

35. Geometric Isomers
Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below)
Trans-2-butene
Substituted groups are on the same side of the double bond (in this case, both are above)
Cis-2-butene

36. Geometric Isomers Trans-2-butene and Cis-2-butene shown on page 754
differ in the geometry of the substituted groups (to double bond)
like other structural isomers, have different physical and chemical properties

37. Optical Isomers
Asymmetric carbon? C with 4 different groups attached. Conceptual Problem 25.12, p.755
Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers.

38. Optical Isomers, and these will each show an assymetric carbon (4 different branches attached)
The assymetric carbon

39. Section 25.4 Hydrocarbon Rings
OBJECTIVES:
Identify cyclic ring structures.

40. Section 25.4 Hydrocarbon Rings
OBJECTIVES:
Describe bonding in benzene.

41. Cyclic Hydrocarbons
The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon
sample drawings on page 759
named as “cyclo- ____”
hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

42. Aromatic Hydrocarbons
A special group of unsaturated cyclic hydrocarbons is known as arenes
contain single rings, or groups of rings
also called “aromatic hydrocarbons”, because of pleasant odor
simplest aromatic is benzene (C6H6)
Term “aromatic” applies to materials with bonding like that of benzene

43. Aromatic Hydrocarbons
Benzene is a six-carbon ring, with alternating double and single bonds
exhibits resonance, due to location of the double and single bonds-p.760
Benzene derivatives possible:
methylbenzene, 3-phenylhexane, ethylbenzene page 761

44. Aromatic Hydrocarbons
Benzene derivatives can have two or more substitutents:
1,2-dimethylbenzene
1,3-dimethylbenzene
1,4-dimethylbenzene
Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 761) C C C C

45. Section 25.5 Hydrocarbons From Earth’s Crust
OBJECTIVES:
Identify three important fossil fuels and describe their origins.

46. Section 25.5 Hydrocarbons From Earth’s Crust
OBJECTIVES:
Describe the composition of natural gas, petroleum, and coal.

47. Section 25.5 Hydrocarbons From Earth’s Crust
OBJECTIVES:
Describe what happens when petroleum is refined.

48. Natural Gas Fossil fuels provide much of the world’s energy
Natural gas and petroleum contain mostly the aliphatic (or straight-chain) hydrocarbons – formed from marine life buried in sediment of the oceans
Natural gas is an important source of alkanes of low molecular mass

49. Natural Gas Natural gas is typically:
80% methane, 10% ethane, 4% propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbons
also contains a small amount of He, and is one of it’s major sources

50. Natural Gas
Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame:
CH4 + 2O2  CO2 + 2H2O + heat
Incomplete burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

51. Petroleum
The compounds found in petroleum (or crude oil) are more complex than those in natural gas
Usually straight-chain and branched-chain alkanes, with some aromatic compounds also
Crude oil must be refined (separated) before being used

52. Petroleum
It is separated by distillation into fractions, according to boiling pt.
Fractions containing higher molar mass can be “cracked” into more useful shorter chain components, such as gasoline and kerosene
involves catalyst and heat
starts materials for plastics and paints

53. Coal
From huge fern trees and mosses decaying millions of years ago under great pressure of rocks / soil.
Stages in coal formation:
1. Peat- soft, fibrous material much like decayed garden refuse; high water content. After drying will make a low-cost, smoky fuel

54. Coal
2. Lignite- peat left in the ground longer, loses it’s fibrous texture, and is also called brown coal
harder than peat; higher C content (50%); still has high water content
3. Bituminous, or soft coal- formed after more time; lower water content, higher C content (70-80%)

55. Coal 4. Anthracite, or hard coal
carbon content exceeding 80%, making it an excellent fuel source
Coal may be found close to the surface (strip-mined), or deep within the earth
Pollutants from coal are common; soot and sulfur problems

56. Note the man standing beside it
BIG BRUTUS
Dragline used to remove the overburden of a strip mining coal field near West Mineral, Kansas
Note the man standing beside it

57. Coal Coal may be distilled for many products
coal gas, coal tar, coke, and ammonia
further distilled into benzene, toluene, naphthalene, phenol- the aromatics
Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes

58. End of Chapter 25