1. Chapter 25 Hydrocarbon Compounds

2. Section 25.1 Hydrocarbons OBJECTIVES:
Describe the bonding in hydrocarbons.

3. Section 25.1 Hydrocarbons OBJECTIVES:
Distinguish between straight-chain and branched-chain alkanes.

4. 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

5. 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

6. Organic Chemistry and Hydrocarbons
Hydrocarbons contain only two elements: hydrogen and carbon
simplest hydrocarbons called alkanes, which contain only single covalent bonds
methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas

7. Organic Chemistry and Hydrocarbons
Review structural formula- p.744
Carbon has 4 valence electrons, thus forms 4 covalent bonds
not only with other elements, but also forms bonds WITH ITSELF.
Ethane (C2H6) is the simplest alkane with a carbon to carbon bond

8. 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
C-C-C C-C-C-C etc.
Names of alkanes always will always end with -ane

9. 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-

10. 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
Condensed structural formulas? Note examples on page 746

11. 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

12. 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

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

15. 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 the -ane ending is now -yl methyl, ethyl, propyl, etc.
Gives much more variety to the organic compounds

16. Branched-Chain Alkanes
Rules for naming - page 748
1. Longest chain is parent
2. Number so branches have low #
3. Give position number to branch
4. Prefix more than one branch
5. Alphabetize branches
6. Use proper punctuation ( - , )

17. Branched-Chain Alkanes
Sample 25-2, page 749
From the name, draw the structure:
1. Find the parent, with the -ane
2. Number carbons on parent
3. Identify substituent groups; attach
4. Add remaining hydrogens
Sample 25-3, page 750

18. Alkanes 3-ethylpentane 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”

19. Section 25.2 Unsaturated Hydrocarbons
OBJECTIVES:
Explain the difference between unsaturated and saturated hydrocarbons.

20. Section 25.2 Unsaturated Hydrocarbons
OBJECTIVES:
Differentiate between the structures of alkenes and alkynes.

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

22. 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 752

23. Alkynes
Hydrocarbons containing carbon to carbon triple bonds called alkynes
-C C-
Alkynes are not plentiful in nature
Simplest is ethyne- common name acetylene (fuel for torches)
Table 25.2, page 753 for b.p. and m.p.

24. Section 25.3 Isomerism OBJECTIVES:
Distinguish among structural, geometric, and stereoisomers.

25. Section 25.3 Isomerism OBJECTIVES:
Identify the asymmetric carbon or carbons in stereoisomers.

26. Structural Isomers
Compounds that have the same molecular formula, but different molecular structures, are called structural isomers
Butane and 2-methylpropane
Also have different properties, such as b.p., m.p., and reactivity

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

28. Geometric Isomers Trans-2-butene and Cis-2-butene shown on page 754
differ only in the geometry of their substituted groups
like other structural isomers, have different physical and chemical properties (also note page 755-top)

29. 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- bottom page 755
Asymmetric carbon? C with 4 different groups attached (Sample 25-4, p.756)

30. Section 25.4 Hydrocarbon Rings
OBJECTIVES:
Identify common cyclic ring structures.

31. Section 25.4 Hydrocarbon Rings
OBJECTIVES:
Explain resonance in terms of the aromatic ring of benzene.

32. 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

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

34. 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 760

35. 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)

36. Section 25.5 Hydrocarbons from the Earth
OBJECTIVES:
Identify three important fossil fuels and describe their origins.

37. Section 25.5 Hydrocarbons from the Earth
OBJECTIVES:
Name some products obtained from natural gas, petroleum, and coal.

38. Natural Gas Fossil fuels provide much of the world’s energy
Natural gas and petroleum contain mostly aliphatic (straight-chain) hydrocarbons
Natural gas is an important source of alkanes of low molecular mass

39. 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

40. 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
Insufficient burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

41. 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

42. 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

43. Coal
From huge fern trees and mosses decaying millions of years ago under great pressure
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

44. 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%)

45. 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

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