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22.2 Unsaturated Hydrocarbons >22.2 Unsaturated Hydrocarbons >

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Chapter 22Hydrocarbon Compounds

22.1 Hydrocarbons

22.2 Unsaturated Hydrocarbons

22.3 Isomers22.4 Hydrocarbon Rings22.5 Hydrocarbons from Earth’s Crust



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What does it mean if a fat is unsaturated?

For example, olives are high in unsaturated fat but low in saturated fat.

CHEMISTRY & YOUCHEMISTRY & YOU



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Alkenes

What are the structural characteristics of alkenes?

AlkenesAlkenes



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• An organic compound that contains the maximum number of hydrogen atoms per carbon atom is called a saturated compound.

• Alkanes are saturated compounds because the only bonds in alkanes are single covalent bonds.

AlkenesAlkenes



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• An organic compound that contains double or triple carbon-carbon bonds is called an unsaturated compound.

• The ratio of the hydrogen atoms to carbon atoms is lower in an unsaturated compound than in a saturated compound.

• An alkene is a hydrocarbon that contains one or more carbon-carbon double covalent bonds.

AlkenesAlkenes



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At least one carbon-carbon bond in an alkene is a double covalent bond. Other bonds may be single carbon-carbon bonds and carbon-hydrogen bonds.

AlkenesAlkenes



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• Ethene (C2H4) is the simplest alkene.

• It is often called by the common name ethylene.

AlkenesAlkenes



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• To name an alkene by the IUPAC system, find the longest chain that contains the double bond.

• This chain is the parent alkene.

• It has the root name of the alkane with the same number of carbons plus the ending -ene.

AlkenesAlkenes



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• The chain is numbered so that the carbon atoms of the double bond have the lowest possible numbers.

• Substituents on the chain are named and numbered in the same way they are for alkanes.

AlkenesAlkenes



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What is the difference between propene and propane?



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What is the difference between propene and propane?

Propene is an alkene with three carbons and one carbon-carbon double bond. Propane is an alkane with three carbons and no carbon-carbon double bonds.



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Describe how saturated and unsaturated fats differ structurally.




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Describe how saturated and unsaturated fats differ structurally.

An unsaturated fat is a fat that contains double or triple carbon-carbon bonds.




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Alkynes

What are the structural characteristics of alkynes?

AlkynesAlkynes



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• A hydrocarbon that contains one or more carbon-carbon triple covalent bonds is called an alkyne.

• A carbon-carbon triple bond is shown in structural formulas as three parallel lines.

AlkynesAlkynes



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At least one carbon-carbon bond in an alkyne is a triple covalent bond. Other bonds may be single or double carbon-carbon bonds and carbon-hydrogen bonds.

• Like alkenes, alkynes are unsaturated compounds.

AlkynesAlkynes



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• Alkynes are not plentiful in nature.

• The simplest alkyne is the gas ethyne (C2H2), which has the common name acetylene, and is shown at left.

• The triple bond restricts rotation in an ethyne molecule, which has a linear shape.

AlkynesAlkynes



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• As a result, the introduction of a double or triple bond into a hydrocarbon does not have a dramatic effect on physical properties such as boiling point.

Like alkanes, the major attractions between alkenes and alkynes are weak van der Waals forces.

Bo

ilin

g p

oin

t (º

C) 0

–20

–40

–60

–80

–100

–120

AlkynesAlkynes



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What is the difference between ethene and ethyne?



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What is the difference between ethene and ethyne?

Ethene is an alkene containing two carbons in a carbon-carbon double bond. Ethyne is an alkyne containing two carbons in a carbon-carbon triple bond.



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At least one carbon-carbon bond in an alkene is a double covalent bond. Other bonds may be single carbon-carbon bonds and carbon-hydrogen bonds.

At least one carbon-carbon bond in an alkyne is a triple bond. Other bonds may be single or double carbon-carbon bonds and carbon-hydrogen bonds.

Key ConceptsKey Concepts



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• saturated compound: an organic compound in which all carbon atoms are joined by single covalent bonds; it contains the maximum number of hydrogen atoms per carbon atom

• unsaturated compound: an organic compound with one or more double or triple carbon-carbon bonds

• alkene: a hydrocarbon containing one or more carbon-carbon double bonds; alkenes are unsaturated hydrocarbons

• alkyne: a hydrocarbon containing a carbon-carbon triple bond; alkynes are unsaturated hydrocarbons

Glossary TermsGlossary Terms



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END OF 22.2END OF 22.2

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carbon carbon double

unsaturated compound

carboncarbon double

single carboncarbon

triple carboncarbon

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