1. Section 4: Hydrocarbon Isomers
Some hydrocarbons have the same molecular formula but have different molecular structures. K
What I Know W
What I Want to Find Out L
What I Learned

2. 2(H) Organize, analyze, evaluate, make inferences, and predict trends from data.
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Hydrocarbon Isomers

3. Essential Questions
How can the two main categories of isomers—structural isomers and stereoisomers—be distinguished?
How are cis- and trans- geometric isomers different?
What is the structural variation in molecules that results in optical isomers?
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Hydrocarbon Isomers

4. Vocabulary Review New electromagnetic radiation isomer
structural isomer
stereoisomer
geometric isomer
chirality
asymmetric carbon
optical isomer
optical rotation
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Hydrocarbon Isomers

5. Structural Isomers
Isomers are two or more compounds that have the same molecular formula but different molecular structures.
Structural isomers have the same chemical formula but their atoms are bonded in different arrangements.
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Hydrocarbon Isomers

6. Structural Isomers
There are two main classes of isomers: structural isomers and stereoisomers.
Structural isomers have different physical and chemical properties.
The structure of a substance determines properties.
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Hydrocarbon Isomers

7. Stereoisomers
Stereoisomers are isomers in which all atoms are bonded in the same order but are arranged differently in space.
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Hydrocarbon Isomers

8. Stereoisomers
Geometric isomers result from different arrangements of groups around a double bond.
Cis means on the same side, and trans means across from.
Geometric isomers have different physical and chemical properties.
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Hydrocarbon Isomers

9. Stereoisomers
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Hydrocarbon Isomers

10. Chirality
The property in which a molecule exists in right and left-handed forms is called chirality.
Louis Pasteur discovered two forms of crystallized tartaric acid.
The forms were mirror images of each other called right and left- handed forms.
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Hydrocarbon Isomers

11. Optical Isomers
Chirality occurs whenever a compound contains an asymmetric carbon.
Asymmetric carbon is a carbon atom that has four different atoms or groups attached to it.
The four groups can be arranged in two different ways.
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Hydrocarbon Isomers

12. Optical Isomers
Isomers that result from different arrangements of four different groups around a carbon atom represent the other class of stereoisomers, called optical isomers.
Optical isomers have the same physical and chemical properties except in chemical reactions where chirality is important.
When polarized light passes through a solution containing an optical isomer, the plane of polarization is rotated to the right by the d-isomer and to the left by the l-isomer, producing and effect called optical rotation.
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Hydrocarbon Isomers

13. Optical Isomers
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Hydrocarbon Isomers

14. Review Essential Questions Vocabulary
How can the two main categories of isomers—structural isomers and stereoisomers—be distinguished?
How are cis- and trans- geometric isomers different?
What is the structural variation in molecules that results in optical isomers?
Vocabulary
isomer
structural isomer
stereoisomer
geometric isomer
chirality
asymmetric carbon
optical isomer
optical rotation
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Hydrocarbon Isomers