1. Chapter 22 “Hydrocarbon Compounds”
Pre-AP Chemistry
Charles Page High School
Stephen L. Cotton

2. Section 22.1 Hydrocarbons
OBJECTIVES:
Describe the relationship between number of valence electrons and bonding in carbon.

3. Define and describe alkanes.
Section 22.1 Hydrocarbons
OBJECTIVES:
Define and describe alkanes.

4. Organic Chemistry and Hydrocarbons
“Organic” originally referred to any chemicals that came from organisms
German chemist Friedrich Wohler synthesized urea in a lab
Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

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

6. 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. These are the Hydrocarbons

7. Organic Chemistry and Hydrocarbons
Hydrocarbons contain only two elements: 1) hydrogen, and 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

8. Organic Chemistry and Hydrocarbons
Review structural formulas - p.694
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

9. Straight-Chain Alkanes
Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain pattern - 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

10. Straight-Chain Alkanes
Combined with the -ane ending is a prefix for the number of carbons
Table 22.1, page 695
Homologous series- a group of compounds that have a constant increment of change
In alkanes, it is: -CH2- (methylene)

11. 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 696

12. 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

13. 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, 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

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

16. Branched-Chain Alkanes
Rules for naming – go from right to left - page 698
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 , )

17. - Page 699

18. 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

19. - Page 700

20. 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”

21. Section 22.2 Unsaturated Hydrocarbons
OBJECTIVES:
Describe the difference between unsaturated and saturated hydrocarbons.

22. Section 22.2 Unsaturated Hydrocarbons
OBJECTIVES:
Distinguish the structures of alkenes and alkynes.

23. 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

24. 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

25. Alkynes
Hydrocarbons containing carbon to carbon triple bonds are 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.
ethyne

26. Section 22.4 Hydrocarbon Rings
OBJECTIVES:
Identify cyclic ring structures.

27. Section 22.4 Hydrocarbon Rings
OBJECTIVES:
Describe bonding in benzene.

28. Cyclic Hydrocarbons
The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon
sample drawings on page 709
named as “cyclo- ____”
hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

29. 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

30. 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.710
Benzene derivatives possible:
methylbenzene, 3-phenylhexane, ethylbenzene (top page 711)

31. Aromatic Hydrocarbons
One derivative of Benzene is called phenylethene, or commonly named STYRENE.
Foamed styrene is trademarked by Dow Chemical as “styrofoam”
Other manufacturers items usually just called “foam cups”
CH2 CH

32. 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 711) C C C C

33. End of Chapter 22