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Chapter 12 Alkenes, Alkynes, and
Aromatic Compounds
12.1
Alkenes and Alkynes
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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Unsaturated Hydrocarbons
Unsaturated hydrocarbons
 have fewer hydrogen atoms
attached to the carbon chain
than do alkanes
 are alkenes with double C=C
bonds
 are alkynes with triple C≡C
bonds
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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Bond Angles in Alkenes
According to VSEPR
theory:
 Three groups in a
double bond are bonded
at 120° angles.
 Alkenes are flat because
the atoms in a double
bond lie in the same
plane.
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
3
Bond Angles in Alkynes
According to VSEPR theory:
 The atoms in a triple bond have a 180° angle.
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
4
Naming Alkenes
The names of alkenes
 use the corresponding alkane name
 change the ending from -ane to -ene
Alkene
H2C=CH2
H2C=CH─CH3
General, Organic, and Biological Chemistry
IUPAC
Common
Ethene
Ethylene
Propene
Propylene
Cyclohexene
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Ethene (Ethylene)
Ethene, or ethylene,
 is the alkene C2H4
 has two carbon atoms
connected by a double bond
 has two H atoms bonded to
each C atom
 is flat with all the C and H
atoms in the same plane
 is used to accelerate the
ripening of fruits
General, Organic, and Biological Chemistry
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Naming Alkynes
The names of alkynes
 use the corresponding alkane name
 change the ending from -ane to -yne
Alkyne
HC≡CH
HC≡C─CH3
General, Organic, and Biological Chemistry
IUPAC
Ethyne
Propyne
Common
Acetylene
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Guide to Naming Alkenes and
Alkynes
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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Example of Naming Alkenes
Write the IUPAC name for CH2═CH─CH2─CH3 and
CH3─CH≡CH─CH3.
STEP 1 Name the longest carbon chain with a double of triple bond:
butene, butyne
STEP 2 Number the chain from the end nearer the
double or triple bond:
CH2═CH─CH2─CH3
1
2
3
4
CH3─CH≡CH─CH3
1
2
3
4
STEP 3 Give the location and name of the double or
triple bond.
1-butene
2-butyne
General, Organic, and Biological Chemistry
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9
Names for Alkanes, Alkenes, and
Alkynes
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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Examples of Naming Alkenes with
Substituents
Write the IUPAC name for
STEP 1 Name the longest carbon chain:
pentene
STEP 2 Number the chain from the end nearer the
double or triple bond:
STEP 3 Give the location and name of the substituent
and double or triple bond:
4-methyl-2-pentene
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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Naming Alkynes with Substituents
Write the IUPAC name for
STEP 1 Name the longest carbon chain:
butyne
STEP 2 Number the chain from the triple bond:
STEP 3 Give the location and name of the substituent
and double or triple bond:
3-Methyl-1-butyne
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
12
Learning Check
Write the IUPAC name for each of the following:
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Solution
Write the IUPAC name for each of the following:
1-butene
2-butene
2-methyl-2-butene
4-methyl-2-pentyne
General, Organic, and Biological Chemistry
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Learning Check
Draw the condensed structural formula for each of the
following:
A. 2-Hexyne
B. 3-Methyl-3-hexene
General, Organic, and Biological Chemistry
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Solution
Draw the condensed structural formula for each of the
following:
A.
2-hexyne
B.
3-methyl-3-hexene
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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