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(H) Organize, analyze, evaluate, make inferences, and predict trends from data. Copyright © McGraw-Hill Education Hydrocarbon Isomers

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? Copyright © McGraw-Hill Education Hydrocarbon Isomers

Vocabulary Review New electromagnetic radiation isomer structural isomer stereoisomer geometric isomer chirality asymmetric carbon optical isomer optical rotation Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

Stereoisomers Stereoisomers are isomers in which all atoms are bonded in the same order but are arranged differently in space. Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

Stereoisomers Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

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. Copyright © McGraw-Hill Education Hydrocarbon Isomers

Optical Isomers Copyright © McGraw-Hill Education Hydrocarbon Isomers

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 Copyright © McGraw-Hill Education Hydrocarbon Isomers