1. Chapter 22 Hydrocarbon Compounds 22.4 Hydrocarbon Rings
22.1 Hydrocarbons
22.2 Unsaturated Hydrocarbons
22.3 Isomers
22.4 Hydrocarbon Rings
22.5 Hydrocarbons from Earth’s Crust
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2. When you hear the word aromatic, you may think of perfume or flowers.
CHEMISTRY & YOU
Does a compound have to be smelly in order to be classified as aromatic?
When you hear the word aromatic, you may think of perfume or flowers.
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3. What is the general structure of a cyclic hydrocarbon?
Cyclic Hydrocarbons
Cyclic Hydrocarbons
What is the general structure of a cyclic hydrocarbon?
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4. Cyclic Hydrocarbons
Not all hydrocarbons are straight chains or branched chains.
In some hydrocarbon compounds, the carbon chain is in the form of a ring.
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5. Cyclic Hydrocarbons
A compound that contains a hydrocarbon ring is called a cyclic hydrocarbon.
Many molecules found in nature contain cyclic hydrocarbons.
Rings with five and six carbons are the most abundant.
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6. Cyclic Hydrocarbons
Just as straight-chain and branched-chain alkanes can be either saturated or unsaturated, so can cyclic hydrocarbons.
A cyclic hydrocarbon that contains only single bonds, and is therefore saturated is called a cycloalkane.
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7. Cyclic Hydrocarbons
To determine the IUPAC name of a cycloalkane, first count the number of carbons in the ring and assign the corresponding alkane name.
Name: propane
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8. Then simply add the prefix cyclo- to the alkane name.
Cyclic Hydrocarbons
To determine the IUPAC name of a cycloalkane, first count the number of carbons in the ring and assign the corresponding alkane name.
Then simply add the prefix cyclo- to the alkane name.
Name: cyclopropane
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9. How many hydrogen atoms will a cycloalkane contain in comparison to a straight chain alkane with the same number of carbons?
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10. How many hydrogen atoms will a cycloalkane contain in comparison to a straight chain alkane with the same number of carbons?
A cycloalkane will contain two fewer hydrogen atoms than a straight chain alkane with the same number of carbons because there is one additional carbon-carbon bond in the cycloalkane.
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11. Aromatic Hydrocarbons
What is the most accurate description of bonding in benzene?
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12. Aromatic Hydrocarbons
There is a class of unsaturated cyclic hydrocarbons that are responsible for the aromas of spices such as vanilla, cinnamon, cloves, and ginger.
These compounds were originally called aromatic compounds because they have distinct, pleasant aromas.
However not all compounds classified has aromatic have pleasant odors, or any odor at all.
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13. Aromatic Hydrocarbons
Benzene is the simplest aromatic compound.
An aromatic compound, or arene, is now defined as an organic compound that contains a benzene ring or other ring in which the bonding is like that of benzene.
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14. Aromatic Hydrocarbons
Any compound not classified as an aromatic compound is an aliphatic compound.
Alkanes, alkenes, alkynes, and cycloalkanes are aliphatic compounds.
The properties of aromatic compounds are quite different from those of aliphatic compounds.
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15. Can you explain what it means if a compound is aromatic?
CHEMISTRY & YOU
Can you explain what it means if a compound is aromatic?
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16. Can you explain what it means if a compound is aromatic?
CHEMISTRY & YOU
Can you explain what it means if a compound is aromatic?
An aromatic compound is defined as an organic compound that contains a benzene ring or other ring in which the bonding is like that of benzene. Some aromatic compounds do have a smell, but not all do.
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17. Aromatic Hydrocarbons
The Structure of Benzene
The benzene molecule is a six-membered carbon ring with one hydrogen atom attached to each carbon.
This arrangement leaves one electron from each carbon free to participate in a double bond.
Two different structures with alternating double bonds can be written for benzene.
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18. Aromatic Hydrocarbons
The Structure of Benzene
These structural formulas show only the extremes in electron sharing between any two adjacent carbons in benzene.
One extreme is a normal single bond. The other extreme is a normal double bond.
Recall that when two equally valid structures can be drawn for a molecule, resonance occurs.
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19. Aromatic Hydrocarbons
The Structure of Benzene
In a benzene molecule, the bonding electrons between carbon atoms are shared evenly around the ring.
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20. Aromatic Hydrocarbons
The Structure of Benzene
Benzene and other molecules that exhibit resonance are more stable than similar molecules that do not exhibit resonance.
Thus, benzene is not as reactive as six carbon alkenes.
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21. Aromatic Hydrocarbons
The Structure of Benzene
Drawing a solid or dashed circle inside a hexagon is a good way to represent benzene in terms of how the electrons are distributed.
However, such a drawing does not show the number of electrons involved.
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22. Aromatic Hydrocarbons
The Structure of Benzene
For this reason, the traditional structure, shown to the right in the series above, is used in this textbook.
Remember, though, that each bond in the ring is identical.
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23. Aromatic Hydrocarbons
Substituted Aromatic Rings
Many dyes used to produce the intense colors of your clothing, such as the blue shown here are substituted aromatic compounds.
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24. Aromatic Hydrocarbons
Substituted Aromatic Rings
Compounds containing substituents attached to a benzene ring are named using benzene as the parent hydrocarbon.
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25. Aromatic Hydrocarbons
Substituted Aromatic Rings
When the benzene ring is a substituent, the C6H5 group is called a phenyl group.
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26. Aromatic Hydrocarbons
Substituted Aromatic Rings
Derivatives of benzene with two substituents are called disubstituted benzenes.
Dimethylbenzene, also called xylene, is an example of a disubstituted benzene.
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27. Aromatic Hydrocarbons
Substituted Aromatic Rings
There are three constitutional isomers for dimthylbenzene (C6H4(CH3)2).
The boiling points of the three compounds are a reminder that constitutional isomers have different physical properties.
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28. Aromatic Hydrocarbons
Substituted Aromatic Rings
In the IUPAC naming system, the possible positions of two substituents in disubstituted benzene are designated as 1,2; 1,3; or 1,4.
Common names for disubstituted benzenes use the terms ortho, meta, and para (abbreviated as o, m, and p) in place of numbers.
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29. How does the reactivity of benzene compare to the reactivity of six-carbon alkenes?
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30. How does the reactivity of benzene compare to the reactivity of six-carbon alkenes?
Benezene is not as reactive as six-carbon alkenes because molecules that exhibit resonance are more stable than similar molecules that do not exhibit resonance.
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31. Key Concepts
In some hydrocarbon compounds, the carbon chain is in the form of a ring.
In a benzene molecule, the bonding electrons between carbon atoms are shared evenly around the ring.
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32. cycloalkane: a cyclic hydrocarbon that contains only single bonds
Glossary Terms
cyclic hydrocarbon: an organic compound that contains a hydrocarbon ring
cycloalkane: a cyclic hydrocarbon that contains only single bonds
aromatic compound: an organic compound that contains a benzene ring or other ring in which the bonding is like that of benzene; aromatic compounds are also known as arenes
aliphatic compound: any compound not classified as an aromatic compound
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33. END OF 22.4
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