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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 three-dimensional structure of the retinal molecule. The structures before and after the light strikes are examples of isomers. You will study different types of isomers.
Structural Isomers • Structural Isomers • How do the properties of structural isomers differ?
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.
Structural Isomers • Structural isomers are compounds that have the same molecular formula, but the atoms are joined together in a different order.
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.
Stereoisomers • Stereoisomers • What are the two types of stereoisomers?
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.
Stereoisomers • Geometric Isomers • Geometric isomers have atoms joined in the same order, but differ in the orientation of groups around a double bond.
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.
Stereoisomers • There is a trans and a cis configuration of 2-butene because a methyl group is attached to each carbon of the double bond.
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.
Stereoisomers • Simulation 28 • Play the isomer game of “Pick the Pairs.”
for Conceptual Problem 22.4 Problem Solving 22.18 Solve Problem 18 with the help of an interactive guided tutorial.
22.3 Section Quiz • 22.3.
22.3 Section Quiz • 1. Structural isomers have different properties because they have • a different number of bonds. • different types of bonds. • different substituents. • a different order of atoms.
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. • cis, trans • trans, cis • trans, iso • stereo, cis
22.3 Section Quiz 3. Geometric isomers have different arrangements of atoms • and different molecular formulas. • but only single bonds. • around an asymetric carbon. • around a double bond.
22.3 Section Quiz • 4. A carbon atom that has four different substituents always forms • an optical isomer. • a saturated hydrocarbon. • a geometric isomer. • an unsaturated hydrocarbon.