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22.4 Hydrocarbon Rings> 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 22 Hydrocarbon Compounds 22.1 Hydrocarbons.

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Presentation on theme: "22.4 Hydrocarbon Rings> 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 22 Hydrocarbon Compounds 22.1 Hydrocarbons."— Presentation transcript:

1 22.4 Hydrocarbon Rings> 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 22 Hydrocarbon Compounds 22.1 Hydrocarbons 22.2 Unsaturated Hydrocarbons 22.3 Isomers 22.4 Hydrocarbon Rings 22.5 Hydrocarbons from Earth’s Crust

2 22.4 Hydrocarbon Rings> 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Does a compound have to be smelly in order to be classified as aromatic? CHEMISTRY & YOU When you hear the word aromatic, you may think of perfume or flowers.

3 22.4 Hydrocarbon Rings> 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Cyclic Hydrocarbons What is the general structure of a cyclic hydrocarbon? Cyclic Hydrocarbons

4 22.4 Hydrocarbon Rings> 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Not all hydrocarbons are straight chains or branched chains. In some hydrocarbon compounds, the carbon chain is in the form of a ring. Cyclic Hydrocarbons

5 22.4 Hydrocarbon Rings> 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A compound that contains a hydrocarbon ring is called a cyclic hydrocarbon. Cyclic Hydrocarbons Many molecules found in nature contain cyclic hydrocarbons. Rings with five and six carbons are the most abundant.

6 22.4 Hydrocarbon Rings> 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Cyclic Hydrocarbons

7 22.4 Hydrocarbon Rings> 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Cyclic Hydrocarbons Name: propane To determine the IUPAC name of a cycloalkane, first count the number of carbons in the ring and assign the corresponding alkane name.

8 22.4 Hydrocarbon Rings> 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Cyclic Hydrocarbons Name: cyclopropane

9 22.4 Hydrocarbon Rings> 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. How many hydrogen atoms will a cycloalkane contain in comparison to a straight chain alkane with the same number of carbons?

10 22.4 Hydrocarbon Rings> 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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.

11 22.4 Hydrocarbon Rings> 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Aromatic Hydrocarbons What is the most accurate description of bonding in benzene? Aromatic Hydrocarbons

12 22.4 Hydrocarbon Rings> 12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons

13 22.4 Hydrocarbon Rings> 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons

14 22.4 Hydrocarbon Rings> 14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons

15 22.4 Hydrocarbon Rings> 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Can you explain what it means if a compound is aromatic? CHEMISTRY & YOU

16 22.4 Hydrocarbon Rings> 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. CHEMISTRY & YOU

17 22.4 Hydrocarbon Rings> 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons The Structure of Benzene

18 22.4 Hydrocarbon Rings> 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. These structural formulas show only the extremes in electron sharing between any two adjacent carbons in benzene. Aromatic Hydrocarbons The Structure of 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.

19 22.4 Hydrocarbon Rings> 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. In a benzene molecule, the bonding electrons between carbon atoms are shared evenly around the ring. Aromatic Hydrocarbons The Structure of Benzene

20 22.4 Hydrocarbon Rings> 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons The Structure of Benzene

21 22.4 Hydrocarbon Rings> 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons The Structure of Benzene

22 22.4 Hydrocarbon Rings> 22 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons The Structure of Benzene

23 22.4 Hydrocarbon Rings> 23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Many dyes used to produce the intense colors of your clothing, such as the blue shown here are substituted aromatic compounds. Aromatic Hydrocarbons Substituted Aromatic Rings

24 22.4 Hydrocarbon Rings> 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Compounds containing substituents attached to a benzene ring are named using benzene as the parent hydrocarbon. Aromatic Hydrocarbons Substituted Aromatic Rings

25 22.4 Hydrocarbon Rings> 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. When the benzene ring is a substituent, the C 6 H 5 group is called a phenyl group. Aromatic Hydrocarbons Substituted Aromatic Rings

26 22.4 Hydrocarbon Rings> 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Derivatives of benzene with two substituents are called disubstituted benzenes. Dimethylbenzene, also called xylene, is an example of a disubstituted benzene. Aromatic Hydrocarbons Substituted Aromatic Rings

27 22.4 Hydrocarbon Rings> 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. There are three constitutional isomers for dimthylbenzene (C 6 H 4 (CH 3 ) 2 ). The boiling points of the three compounds are a reminder that constitutional isomers have different physical properties. Aromatic Hydrocarbons Substituted Aromatic Rings

28 22.4 Hydrocarbon Rings> 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Aromatic Hydrocarbons Substituted Aromatic Rings

29 22.4 Hydrocarbon Rings> 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. How does the reactivity of benzene compare to the reactivity of six- carbon alkenes?

30 22.4 Hydrocarbon Rings> 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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.

31 22.4 Hydrocarbon Rings> 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Key Concepts

32 22.4 Hydrocarbon Rings> 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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 Glossary Terms

33 22.4 Hydrocarbon Rings> 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF 22.4


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