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Chemistry 22.3

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22.3

Isomers

The retinal molecule in the rod and
cone cells of your eye has a
hydrocarbon skeleton. When light
strikes a cell containing retinal, it
causes a change in the threedimensional structure of the retinal
molecule. The structures before and
after the light strikes are examples of
isomers. You will study different
types of isomers.
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22.3

Isomers

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Structural Isomers

Structural Isomers
How do the properties of structural
isomers differ?

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22.3

Isomers

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Structural Isomers

Compounds that have the same molecular
formula but different molecular structures are
called isomers.
Structural isomers differ in physical
properties such as boiling point and
melting point. They also have different
chemical reactivities.

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22.3

Isomers

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Structural Isomers

Structural isomers are compounds that have
the same molecular formula, but the atoms are
joined together in a different order.

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22.3

Isomers

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Structural Isomers

Both butane and 2-methylpropane have the
molecular formula C4H10. The atoms in their
molecules are arranged in a different order, so
they are structural isomers.

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22.3

Isomers

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Stereoisomers

Stereoisomers
What are the two types of
stereoisomers?

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22.3

Isomers

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Stereoisomers

Two types of stereoisomers are geometric
isomers and optical isomers.

Stereoisomers are molecules in which the
atoms are joined in the same order, but the
positions of the atoms in space are different.

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22.3

Isomers

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Stereoisomers

Geometric Isomers
Geometric isomers have atoms joined in the
same order, but differ in the orientation of groups
around a double bond.

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22.3

Isomers

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Stereoisomers

In the trans configuration, the methyl groups
are on opposite sides of the double bond.

In the cis configuration, the methyl groups are
on the same side of the double bond.

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22.3

Isomers

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Stereoisomers

There is a trans and a cis configuration of 2butene because a methyl group is attached to
each carbon of the double bond.

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22.3

Isomers

>

Stereoisomers

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22.3

Isomers

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Stereoisomers

Optical Isomers

• A carbon with four different atoms or groups
attached is an asymmetric carbon.

• Pairs of molecules that differ only in the way
that four different groups are arranged around
a central carbon atom are called optical
isomers.

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Isomers

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Stereoisomers

Simulation 28
Play the isomer game of “Pick the Pairs.”

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Practice Problems for Conceptual Problem 22.4

Problem Solving 22.18 Solve
Problem 18 with the help of an
interactive guided tutorial.
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22.3 Section Quiz

Assess students’ understanding
of the concepts in Section 22.3.
Continue to:

-or-

Launch:

Section Quiz

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22.3 Section Quiz
1. Structural isomers have different properties
because they have
a. a different number of bonds.
b. different types of bonds.
c. different substituents.
d. a different order of atoms.

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22.3 Section Quiz
2

Substituent groups on opposite sides of a
double bond are said to be in the _______
configuration. If the groups are on the
same side of the bond, then they are in the
_______ configuration.

a. cis, trans
b. trans, cis
c. trans, iso
d. stereo, cis
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22.3 Section Quiz
3. Geometric isomers have different
arrangements of atoms
a. and different molecular formulas.
b. but only single bonds.
c. around an asymetric carbon.
d. around a double bond.

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22.3 Section Quiz
4. A carbon atom that has four different
substituents always forms
a. an optical isomer.
b. a saturated hydrocarbon.
c. a geometric isomer.
d. an unsaturated hydrocarbon.

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