Alkenes & Alkynes I

1. Alkenes & Alkynes I Properties and Synthesis

2. Alkenes & Alkynes Chapter 7 • Physical Properties of Alkenes & Alkynes • E-Z System • Vicinal (Vic) & Geminal (Gem) • Relative Stabilities of Alkenes & Cycloalkenes • Zaitsev’s Rule & Hofmann Rule • Dehydration of Alcohols • Terminal Alkynes • Syn & Anti Additions • Hydrogenation of Alkynes • Index of Hydrogen Deficiency

3. Physical Properties • Factors • Intermolecular Forces (IMF) • Molecular Weight (MW) • Symmetry

4. Boiling Point Trends-General Ethene -104 0C 2C Propene -47 0C 3C 1-Butene -6.3 0C 4C 1-Pentene 30 0C 5C 1-Hexene 63 0C 6C 1-Heptene 94 0C 7C As Molecular Weight Increases Boiling Point (BP) increases.

5. Boiling Point Trends-Branching Branching decreases boiling point due to decrease surface area which translates into fewer surface electrons participating in building intermolecular forces (IMF).

6. Boiling Point Trends-Branching • 1-Pentene 30 0C • 2-Methyl-1-butene 31 0C • Basically no significant difference in BP.

7. Sharing the Burden (Concept Review) The more the molecule can spread out the burden (Charge, Pi electrons, free radical, etc.) the more stable the molecule will be.

8. Sharing the Burden • Ability to spread out the burden of the double bond translates into greater stability. • Pi electrons have greater flow with more Beta-Carbons.

9. Boiling Point Trends-Branching • Branching decreases boiling point due to decrease surface area which translates into fewer surface electrons participating in building intermolecular forces. • Branching of Alkenes leads to greater flow of Pi electrons which can participate in building intermolecular forces. • The two factors together cancel each other out resulting in no significant change in BP

10. Boiling Point Trends-Cis/Trans • Analyze the handout (Chart with Physical Properties of Alkenes) Dipole Moments

11. Boiling Point Trends-Cis/Trans • Cis has a higher BP than Trans due to the stronger dipole of the Cis.

12. BP Trends-Cis/Trans vs. Terminal • Analyze the handout (Chart with Physical Properties of Alkenes) H CH3CH2 Dipole Moments 1-Butene

13. BP Trends-Cis/Trans & Terminal • Cis & Trans have higher BP than terminal alkenes due to increase flow of Pi electrons resulting in stronger IMF. • Cis has a higher BP than Trans due to the stronger dipole of the Cis.

14. Alkane vs. Alkene Boiling Point • -88.6 0C -104 0C • -42.1 0C -47 0C • -0.5 0C -6.3 0C • 36.1 0C 30 0C • 68.7 0C 63 0C • 98.4 0C 94 0C Decreased Decreased Decreased Decreased Decreased Decreased

15. Alkane vs. Alkene Boiling Point • Adding a double bond decreases the BP due to decreased sigma electrons participating in building IMF. • Why do Cis and Trans Butene have higher BP’s than Butane?

16. Melting Point Trends-General Ethene -169 0C 2C Propene -185 0C 3C 1-Butene -185 0C 4C 1-Pentene -165 0C 5C 1-Hexene -140 0C 6C 1-Heptene -119 0C 7C As Molecular Weight Increases Melting Point (MP) increases, except where symmetry plays a role.

17. Melting Point Trends-Branching • No general trend • If branching increases symmetry, melting point (MP) increases. • If branching decreases symmetry, melting point decreases

18. Melting Point Trends-Cis/Trans • Analyze the handout (Chart with Physical Properties of Alkenes) Planes of Symmetry One Plane of Symmetry Two Planes of Symmetry

19. Melting Point Trends-Cis/Trans • Trans has a higher MP than Cis due to the greater symmetry. Trans has two planes of symmetry, while Cis only has one plane of symmetry.

20. Melting Point Trends-Cis/Trans • Analyze the handout (Chart with Physical Properties of Alkenes) H CH3CH2 Planes of Symmetry 1-Butene One Plane of Symmetry Two Planes of Symmetry No

21. Melting Point Trends-Cis/Trans • Cis & Trans have higher MP than terminal alkenes due to greater symmetry • Trans has a higher MP than Cis due to the greater symmetry. Trans has two planes of symmetry, while Cis only has one plane of symmetry.

22. Alkane vs. Alkene Melting Point Increased • -183 0C -169 0C • -188 0C -185 0C • -138 0C -185 0C • -130 0C -165 0C • -95 0C -140 0C • -910C -119 0C Non-Significant Decreased Decreased Decreased Decreased

23. Alkane vs. Alkene Melting Point • Adding a double bond in a central location increases symmetry and thus increases MP. • Adding a double bond in a non-central location decreases symmetry and thus decreases MP. • How does Cis and Trans Butene MP compared to the MP of Butane? How do you explain this?

24. Saturated & Unsaturated • Saturated – The carbon atoms of the molecule are complete filled with Hydrogen (No double or triple bonds) • Unsaturated-Some carbon atoms have room for additional hydrogen (Double or triple bonds present) • Polyunsaturated-Many carbon atoms have room for additional hydrogen (Many Double or triple bonds present)

25. Saturated & Unsaturated • Saturated – CH3CH2CH2CH2CH2CH2CH2CH3 • Unsaturated- CH3CH=CHCH2CH2CH2CH2CH3 CH3CH=CHCH2CH=CHCH2CH3 • Polyunsaturated- CH2=CHCH=CHCH=CHCH=CH2 • Fatty Acid- CH3CH2CH2CH2CH2CH2CH2COOH

26. Saturated & Unsaturated Fatty Acids Source: http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/fatcatab.htm

27. Saturated & Unsaturated Fats Source: http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/fatcatab.htm

28. Saturated & Unsaturated Fats

29. Saturated & Unsaturated Fatty Acids

30. Phospholipids Source: http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/lipid.htm#animat2

31. Cell Membrane Fluidity

32. R-S System (Concept Review)

33. E-Z System • E • Entgegen (Opposite) • Z • Zusammen (Together)

34. E-Z System (E) Opposite (Z) Together

35. E-Z System Problem 7.1 Page 284 (A-D) • Answers: • (E)-1-bromo-1-chloro-1-pentene • (E)-2-bromo-1-chloro-1-iodo-1-butene • (Z)-3,5-dimethyl-2-hexene • (Z)-1-chloro-1-iodo-2-methyl-1-butene

36. Vic vs. Gem • Vic CH2BrCH2Br • Vicinal • Latin Vicinus meaning adjacent • Used when groups are on adjacent Carbons • Gem CHBr2CH3 • Geminal • Latin Geminus meaning twins • Used when groups are on the same Carbon

37. Stabilities of Alkenes-General • Ability to spread out the burden of the double bond translates into greater stability.

38. Stabilities of Alkenes-(Cis/Trans) • Trans is more stable due to less crowding, less electron repulsion.

39. Stabilities of Alkenes-(Cis/Trans) • Cis is more stable due to less ring strain, less electron repulsion. • Ring strain electron repulsion is stronger than crowding electron repulsion.

40. Vision & Cis-Trans Stability

41. Stabilities of Alkenes-(Cis/Trans) • Gem is more stable than Vic due to greater electron flow.

42. Zaitsev Rule • Zaitsev, Saytzeff, Saytseff, Saytzev • States that the major product of an elimination reaction will be the more stable alkene. * Major Product

43. Zaitsev Rule • Zaitsev, Saytzeff, Saytseff, Saytzev • States that the Major product of an elimination reaction will be the more stable alkene • Ea driven reaction (Kinetic Control)

44. Ea driven reaction (Kinetic Control) • Rate of formation of the product with the lower Ea is faster, thus it accumulates faster.

45. Ea driven reaction (Kinetic Control)

46. Hofmann Rule • Opposite of Zaitsev Rule • Applies when major product of an elimination reaction is the less stable alkene. • Collision Driven Reaction

47. Hofmann Rule

48. Ea vs. Collision CH3CHBrCH(CH3)2 + NU:- E2 E2 SN2 CH3CH=C(CH3)2 CH2=CHCH(CH3)2

49. Ea vs. Collision • SN2 vs. E2 • E2 (Zaitsev) vs. E2 (Hofmann)

50. Dehydration of Alcohols • Elimination Reaction • Acid Catalyzed • Products alkene or alkyne & water