Chapter 12 Alkenes Alkynes and Aromatic Compounds 12

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Chapter 12 Alkenes, Alkynes, and Aromatic Compounds 12. 2 Cis–Trans Isomers General, Organic, and

Chapter 12 Alkenes, Alkynes, and Aromatic Compounds 12. 2 Cis–Trans Isomers General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1

Cis and Trans Isomers In an alkene, cis and trans isomers are possible because

Cis and Trans Isomers In an alkene, cis and trans isomers are possible because the double bond § is rigid § cannot rotate § has groups attached to the carbons of the double bond that are fixed relative to each other General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2

Cis–Trans Isomers Cis–trans isomers can be modeled by § making a “double bond” with

Cis–Trans Isomers Cis–trans isomers can be modeled by § making a “double bond” with your fingers with both thumbs on the same side (cis isomer) § or fingers with thumbs on opposite sides from each other (trans isomer) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3

Cis–Trans Isomers (continued) Cis–trans isomers occur when different groups are attached to the double

Cis–Trans Isomers (continued) Cis–trans isomers occur when different groups are attached to the double bond. § In a cis isomer, groups are attached on the same side of the double bond. § In the trans isomer, the groups are attached on opposite sides of the double bond. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 4

Naming Cis–Trans Isomers § The prefixes cis- or trans- are placed in front of

Naming Cis–Trans Isomers § The prefixes cis- or trans- are placed in front of the alkene name when there are cis–trans isomers. cistrans- cis-1, 2 -Dibromoethene trans-1, 2 -Dibromoethene General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 5

Cis–Trans Isomerism § Cis–trans isomers do not occur if a carbon atom in the

Cis–Trans Isomerism § Cis–trans isomers do not occur if a carbon atom in the double bond is attached to identical groups. (not cis or trans) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6

Pheromones A pheromone § is a chemical messenger emitted by insects in tiny quantities

Pheromones A pheromone § is a chemical messenger emitted by insects in tiny quantities § called bombykol is emitted by the silkworm moth to attract other moths and has one cis and one trans double bond General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7

Learning Check Name each, using cis–trans prefixes when needed. General, Organic, and Biological Chemistry

Learning Check Name each, using cis–trans prefixes when needed. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 8

Solution cis-1, 2 -Dibromoethene trans-2 -Butene 1, 1 -Dichloropropene Identical atoms; no cis or

Solution cis-1, 2 -Dibromoethene trans-2 -Butene 1, 1 -Dichloropropene Identical atoms; no cis or trans General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9

ALKENES ALKYNES AND AROMATIC COMPOUNDS Alkenes contain atALKENES ALKYNES AND AROMATIC COMPOUNDS Alkenes contain at
Aromatic compounds Aromatic compounds l Aromatic compounds areAromatic compounds Aromatic compounds l Aromatic compounds are
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Chapter 12 Alkenes Alkynes and Aromatic Compounds 12Chapter 12 Alkenes Alkynes and Aromatic Compounds 12
Chapter 12 Alkenes Alkynes and Aromatic Compounds 12Chapter 12 Alkenes Alkynes and Aromatic Compounds 12
Chapter 12 Alkenes Alkynes and Aromatic Compounds withChapter 12 Alkenes Alkynes and Aromatic Compounds with