1. 5-1 5 Organic Chemistry William H. Brown & Christopher S. Foote

2. 5-2 5 Alkenes I Chapter 5

3. 5-3 5 Unsaturated Hydrocarbons  Unsaturated hydrocarbon:  Unsaturated hydrocarbon: contains one or more carbon-carbon double or triple bonds  Alkene:  Alkene: contains a carbon-carbon double bond and has the general formula C n H 2n  Alkyne:  Alkyne: contains a carbon-carbon triple bond and has the general formula C n H 2n-2

4. 5-4 5 Unsaturated Hydrocarbons  Arenes:  Arenes: benzene and its derivatives (Ch 20-21)

5. 5-5 5 Benzene & Phenyl Group  We do not study benzene and its derivatives until Chapters 20 & 21 but, we show structural formulas of compounds containing the phenyl group before that time the phenyl group is not reactive under any of the conditions we describe in Ch 6-19

6. 5-6 5 Structure of Alkenes  The two carbon atoms of a double bond and the four atoms attached to them lie in a plane, with bond angles of approximately 120°  A double bond consists of one sigma bond formed by overlap of sp 2 hybrid orbitals one pi bond formed by overlap of parallel 2p orbitals it takes approx. 264 kJ (63 kcal)/mol to break the pi bond in ethylene

7. 5-7 5 Restricted rotation about C=C

8. 5-8 5 Cis,Trans Isomerism  Cis,trans isomers:  Cis,trans isomers: isomers that have the same connectivity but a different arrangement of their atoms in space due to the presence of a ring or a carbon-carbon double bond

9. 5-9 5 IUPAC Nomenclature 1. Number the longest chain of carbon atoms that contains the double bond in the direction that gives the carbons of the double bond the lowest numbers 2. Locate the double bond by the number of its first carbon 3. Name substituents 4. Number the carbon, locate and name substituents, locate the double bond, and name the main chain.

10. 5-10 5 Alkenyl Groups

11. 5-11 5 Common Names  Despite the precision and universal acceptance of IUPAC nomenclature, some alkenes, particularly low-molecular-weight ones, are known almost exclusively by their common names

12. 5-12 5 Configuration  The cis,trans system:  The cis,trans system: configuration is determined by the orientation of atoms of the main chain

13. 5-13 5 Configuration - E,Z uses priority rules (Chapter 3) if groups of higher priority are on the same side, configuration is Z (German, zusammen) if groups of higher priority are on opposite sides, configuration is E (German, entgegen)

14. 5-14 5 Configuration - E,Z Example: Example: name each alkene and specify its configuration by the E,Z system

15. 5-15 5 Cis,Trans Isomerism  Cycloalkenes configuration of the double bond in cyclopropene through cycloheptene must be cis cyclopentene is only slightly puckered

16. 5-16 5 Cis,Trans Isomerism the configuration of the double bond in cyclohexene must be cis cyclohexene is puckered

17. 5-17 5 Cis,Trans Isomerism  Cycloalkenes trans-cyclooctene is the smallest trans-cycloalkene stable at 25°C the cis isomer is 38 kJ (9.1 kcal)/mol more stable than the trans isomer.

18. 5-18 5 Physical Properties  Alkenes are nonpolar compounds  The only attractive forces between their molecules are dispersion forces  The physical properties of alkenes are similar to those of alkanes

19. 5-19 5 Terpenes  Terpene:  Terpene: a compound whose carbon skeleton can be divided into two or more units identical with the carbon skeleton of isoprene

20. 5-20 5 Terpenes  Myrcene, C 10 H 16, a component of bayberry wax and oils of bay and verbena  Menthol, from peppermint

21. 5-21 5 Terpenes  -Pinene, from turpentine camphor, from the camphor tree

22. 5-22 5 Terpenes  Vitamin A (retinol) how many stereoisomers are possible for this terpene alcohol?

23. 5-23 5 Prob 5.7 Using the VSEPR model, predict all bond angles about each circled atom.

24. 5-24 5 Prob 5.12 Name these alkenes and cycloalkenes.

25. 5-25 5 Prob 5.13 Arrange the groups in each set in order of increasing priority.

26. 5-26 5 Prob 5.14 Assign an E or Z configuration to each compound. Also assign a cis or trans configuration to each.

27. 5-27 5 Prob 5.16 For each molecule that shows cis,trans isomerism, draw the cis isomer.

28. 5-28 5 Prob 5.17 Draw structural formulas for all compounds of molecular formula C 5 H 10 that are (a) alkenes that do not show cis,trans isomerism. (b) alkenes that do show cis,trans isomerism. (c) cycloalkanes that do not show cis,trans isomerism. (d) cycloalkanes that do show cis,trans isomerism.

29. 5-29 5 Prob 5.19 Draw a structural formula of a bromoalkene of molecular formula C 5 H 9 Br that shows (a) neither E,Z isomerism nor chirality. (b) E,Z isomerism but not chirality. (c) chirality but not E,Z isomerism. (d) both chirality and E,Z isomerism.

30. 5-30 5 Prob 5.23 Which alkenes exist as pairs of cis,trans isomers? For each that does, draw the trans isomer.

31. 5-31 5 Prob 5.24 Show that four stereoisomers are possible for this compound. Draw the stereoisomer with an E configuration at the double bond and an R configuration at the stereocenter.

32. 5-32 5 Prob 5.28 Show that warburganal is a terpene. Label all stereocenters and state how many stereoisomers are possible for a molecule of this structure.

33. 5-33 5 Prob 5.29 Show that santonin is a terpene. Label all stereocenters and tell how many stereoisomers are possible for the molecule of this structure.

34. 5-34 5 Prob 5.30 (a) Show that zoapatanol is a terpene. (b)Specify the configuration at the double bond to the seven-membered ring. (c) How many stereoisomers are possible for this molecule?

35. 5-35 5 Prob 5.31 Pyrethrin II Label all stereocenters in pyrethrin II. How many stereoisomers are possible for this molecule?

36. 5-36 5 Prob 5.31 Pyrethrosin Show that pyrethrosin is a terpene. Label all stereocenters in pyrethrosin and state how many stereoisomers are possible for it.

37. 5-37 5 Alkenes I End Chapter 5