1. DUCS First General Meeting!
Liquid Nitrogen Ice Cream!
Tie-dye your lab coat!
Monday, Sept. 22nd
4:45pm
HS-4

2. CycloAlkanes and their Stereochemistry
Organic Chemistry I
Fall, 2014
Day 8
9/19/14
Chapter 3
Chapter 4
CycloAlkanes and their Stereochemistry
Chem Act 7A & 7B

3. How many H’s are on this molecule?12 14 16 17 18 20
Other
Countdown 10

4. How many units (degrees) of unsaturation?3 4 5 6 7 8 9
Countdown 10

5. What are the numbers of primary, secondary, tertiary and quaternary carbons in this molecule?
2, 3, 3, 2
3, 4, 2, 1
3, 3, 3, 1
3, 4, 3, 0

6. What are the numbers of primary, secondary, tertiary and quaternary hydrogens in this molecule?
6, 6, 2, 1
9, 8, 2, 1
9, 8, 3, 1
9, 8, 3, 0

7. Acyclic alkanes are non-rigid

8. Cyclic Alkanes are “rigid”

9. The Dance of Ethane Conformational Isomers

10. Which statement about bond rotation around the C-C bonds in ethane and ethene is correct? H3C-CH3 H2C=CH2
Rotation around a σ bond is easy because the orbital overlap does not change with rotation.
Rotation around a π bond is easy because there are p orbitals available in all directions of space.
Rotation around a σ bond is hard because the electron pairs from the adjacent bonds must pass by each other.
Rotation around a π bond is hard because the electrons are delocalized.
Rotation around σ and π bonds is equally facile.

11. The Dance of Propane

12. The Dance of Butane Conformational Isomers

13. Melvin Newman Projections (1952)

14. Non-Bonded Intramolecular Interactions McMurry 3
Non-Bonded Intramolecular Interactions McMurry 3.42 Draw low and high energy Newman conformations of 2-methylbutane

15. Which of the above represents a Newman projection of 2-bromo-3-chlorobutane?d e

16. Some Cyclic Natural Products

17. Tamiflu

18. Some Cyclic Hydrocarbons CnH2n vs CnH2n+2

19. Chem Activity 7A Cis and Trans Rings (p. 98)
Read Model 1 and complete CTQ 1-4.
If you finish, continue to Model 2.
Note for CTQ 7: We are skipping alkenes (E/Z isomers) for now. Ignore those!

20. Cycloalkanes - Physical Properties

21. Cyclopropane C3H6

22. Cyclopropane Stereoisomers

23. Cyclobutane C4H8

24. Cyclopentane C5H10

25. Some Natural Cyclopentanes The Prostaglandins

26. Are these two molecules the same?
No; one is cis and one is trans.
No; the methyl groups are not on the same side of the ring.
Yes; they have the same #s of C’s and H’s.
Yes; they can be interconverted without breaking bonds.
Yes; they have the same stereochemistry

27. Which of these 4 molecules are the same?
A & B and C & D
A & C and B & D
A & D and B & C
None are the same.
All are the same.

28. CnH2n + 2nO2 = nCO2 + 2nH2O

29. What kind of strain is there and Which cycloalkane is most strain free ?

30. Nomenclature with rings

31. Problem 4.1

34. Cyclohexane and its Stereochemistry
Organic Chemistry I
Fall, 2014
Day 8
9/19/14
Chapter 4
Cyclohexane and its Stereochemistry
Chem Act 7A, 7B - Today

35. Cyclohexane C6H12 and Analogs

36. Visualizing Cyclohexane The Chair – Chem Act 7B Model 3

38. What kind of strain is there and Which cycloalkane is most strain free ?
Chem Act 7B Model 4

39. CnH2n + 2nO2 = nCO2 + 2nH2O

40. Axial and Equatorial Chem Act 7B Model 5
Axial and Equatorial Chem Act 7B Model 5

41. What happens to an axial hydrogen in a chair conformation of cyclohexane when all bonds “rotate” in a synchronized fashion?
nothing, it stays where it was as an axial H
it “flips” to the equatorial position on the same carbon
it “flips” to the equatorial position on the next carbon
the carbon to which the hydrogen is attached changes hybridization
it moves from a cis to a trans position

42. Strain in Substituted Cyclohexanes
ΔG = - RT ln K
ΔG (in kcal/mole) = log K
K log K ΔG
Why so large ?
Why so small ?

43. Substituted Cyclohexanes

44. What happens to a substituent in a chair conformation of cyclohexane when all bonds “rotate” in a synchronized fashion?
nothing, it stays where it was in an axial position
it “flips” to the equatorial position on the same carbon
it moves to the next carbon
the carbon to which the substituent is attached changes hybridization
it moves from a cis to a trans position

45. Which of these 4 molecules have the same relative stereochemistry ?
A & B and C & D
A & C and B & D
A & D and B & C
None have the same.
All have the same.

46. What is the relationship between A and B (or C and D) ?
Constitutional isomers
Conformational isomers
Configurational isomers
They have different molecular weights.
All are the same.

47. 1,2-Dimethylcyclohexane

48. What is the energy difference between the two chair conformations of trans-1,2-dimethylcyclohexane?
zero
one gauche interaction vs two CH3-H diaxial interactions
one gauche interaction vs four CH3-H diaxial interactions
two gauche interactions vs four CH3-H diaxial interactions
one gauche interaction vs two gauche interactions

49. Problem 4.18 Draw the most stable chair conformation of
a) trans-1-Chloro-3-methylcyclohexane
b) cis-1-Ethyl-2-methylcyclohexane
c) cis-1-Bromo-4-ethylcyclohexane
d) cis-1-tert-Butyl-4-ethylcyclohexane

50. Which of the above molecules represents the most stable conformation of trans-1,3-dimethylcyclohexane? a b c d e

51. Which of the above molecules will have the highest energy after the chair flip?d e

52. Which of the above structures represents the most stable (lowest PE) conformation of tert-butyl-3,5-dimethylcyclohexane? a b c d e

53. Which of the above structures represents the least stable (highest PE) conformation of tert-butyl-3,5-dimethylcyclohexane? a b c d e

56. What are the relative geometries of ring fusions (starting from the left) for the steroid shown below?
cis, cis, cis
cis, cis, trans
cis, trans, trans
trans. cis, cis
trans, trans, cis

57. Substituted Cyclohexanes

58. Decalin C10H18

59. Reactions of Alkanes