1. Important Alkenes in Nature
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Klein, Organic Chemistry 2e

2. Alkenes in Pheromones Klein, Organic Chemistry 2e
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Klein, Organic Chemistry 2e

3. Alkenes in industry
70 billion pounds of propylene (propene) and 200 billion pounds of ethylene (ethene) are both made from cracking petroleum each year. They are mainly used for making plastics.
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Klein, Organic Chemistry 2e

4. Alkenes as precursor in Synthesis
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Klein, Organic Chemistry 2e

5. Alkene Nomenclature
Alkenes are named using the same procedure for alkanes with minor modifications
*Identify the parent chain, which should include the C=C double bond.
Identify and Name the substituents
*Assign a locant (and prefix if necessary) to each substituent. Give the C=C double bond(s) the lowest number possible
List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso)
*The C=C double bond locant is placed either just before the parent name or just before the -ene suffix
More than one C=C bond: add prefix before “-ene”.
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

6. Parent Chain Must have C=C bond
Identify the parent chain, which should include the C=C double bond
The name of the parent chain should end in -ene rather than –ane
The parent chain should include the C=C double bond
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

7. Nomenclature: C=C bond as lowest #
Identify and Name the substituents
Assign a locant (and prefix if necessary) to each substituent. Give the C=C double bond the lowest number possible
Parent chain: 2-heptene 5-heptene (wrong)
The locant is ONE number, NOT two. Although the double bond bridges carbons 2 and 3, the locant is the lower of those two numbers
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

8. Parent chain
List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso)
The C=C locant is placed either just before the parent name or just before the -ene suffix.
Prefix added (eg. heptatriene) if more than one C=C in parent chain
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

9. Alkene Isomerism: cis/trans
For the pi bond to remain intact, rotation around a double bond is prohibited
cis and trans structures are not identical
cis-butane is more polar and higher energy (eclipsed) than trans-butane
Cis/trans designation are strictly used to describe C=C double bonds with identical groups (H atom) on each carbon.
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

10. Cis/trans in Cycloalkene
In cyclic alkenes with less than 8 atoms in the ring, only cis alkenes are stable.
trans-cyclooctene
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Klein, Organic Chemistry 2e

11. E/Z designation: Priority of Groups
Assigning E or Z to a stereoisomers
prioritize the groups attached to the C=C double bond based on atomic number (similar to R/S chiral center configuration)
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Klein, Organic Chemistry 2e

12. E vs. Z Assigning E or Z to a stereoisomers
prioritize the groups attached to the C=C double bond based on atomic number
If the top priority groups are on the same side of the C=C double bond, it is Z (for zussamen, which means together)
If the top priority groups are on opposite sides of the C=C double bond, it is E (for entgegen, which means opposite)
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13. Unsaturated groups in OChem
Vinyl
Allyl
Benzyl
Aryl

14. Practice: Alkene Nomenclature
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Klein, Organic Chemistry 2e

15. Alkene Stability: Trans vs. Cis
Steric strain (like eclipsed conformation in alkane), cis isomers are generally less stable than trans
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

16. Practice: Alkene Nomenclature
E-1-cyclohexyl-1,3,3-trimethyl-1-butene
3E,8Z-6-allylic-5-ethyl-7-vinyl-1,3,8-octatriene
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

17. Practice: Alkene Nomenclature
Parent chain: 1-butene or but-1-ene
Substituent: cyclohexyl; three methyl
E isomer
E-1-cyclohexyl-1,3,3-trimethyl-1-butene
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Klein, Organic Chemistry 2e

18. Practice Problems Name the following molecules
3,3-dichloro-6-bicyclo[3.2.1]octene
R-Z-3,4-dimethyl-2-hexene
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Klein, Organic Chemistry 2e

19. Additional Practice Problems
NAME the following compounds, using either cis or trans and either E or Z where appropriate
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Klein, Organic Chemistry 2e