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Geometric ISOMERS of Alkenes Chapter 12 Section 3.

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Presentation on theme: "Geometric ISOMERS of Alkenes Chapter 12 Section 3."— Presentation transcript:

1 Geometric ISOMERS of Alkenes Chapter 12 Section 3

2  The CARBON – CARBON double bond is rigid (no free rotation) because of the shapes of the orbitals involved in its formation Pi bond Sigma bond 2 p-orbital electronsthe electrons lie lie above and belowin a line between the 2 carbons the 2 carbon nuclei Rotation around the double bond is restricted because the pi bond would have to be broken to allow for rotation. THUS, THE DOUBLE BOND IS RIGID ALKENES

3 In cycloalkanes, cis/trans applied to the branches trans = on OPPOSITE sides of the ring cis = on the SAME side of the ring Geometric Isomers

4 In alkenes, cis/trans applies to the location of the parent chain around the double bond, NOT the branches Geometric Isomers

5 If one of the carbons of the double bond has 2 identical substituents there are NO cis/trans isomers. Geometric Isomers

6 1,1-dichloroethene no cis/trans because both carbons have identical substituents 1,2-dichloroethene cis/trans isomers DO exist in this molecule Example:

7  1-pentene  3-ethyl-3-hexene  3-methyl-2-pentene Which exist as geometric isomers?

8  Cis-3-octene  Trans-5-chloro-2-hexene  Trans-2,3-dichloro-2-butene Draw these molecules.

9  3 RD EDITION: P351 #19, 23, 24, 26  4 TH EDITION: P359 #21, 25, 26, 28 HOMEWORK


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