1. Conformational Analysis Newman Projections Ring Strain Cyclohexane Conformations

2. Views of Ethane

3. The Newman Projection

4. Rotational Conformations of Ethane

5. Definitions Conformations - Different spatial arrangments that a molecule can adopt due to rotation about sigma bonds. Staggered - A low energy conformation where the bonds on adjacent atoms bisect each other (60 o dihedral angle), maximizing the separation. Eclipsed - A high energy conformation where the bonds on adjacent atoms are aligned with each other (0 o dihedral angle).

6. 60 o Rotation Causes Torsional or Eclipsing Strain

7. Types of Strain Steric - Destabilization due to the repulsion between the electron clouds of atoms or groups. Groups try to occupy some common space. Torsional - Destabilization due to the repulsion between pairs of bonds caused by the electrostatic repulsion of the electrons in the bonds. Groups are eclipsed. Angle - Destabilisation due to distortion of a bond angle from it's optimum value caused by the electrostatic repulsion of the electrons in the bonds. e.g. cyclopropane

8. Definitions Anti - Description given to two substitutents attached to adjacent atoms when their bonds are at 180 o with respect to each other. Syn - Description given to two substitutents attached to adjacent atoms when their bonds are at 0 o with respect to each other. Gauche - Description given to two substitutents attached to adjacent atoms when their bonds are at 60 o with respect to each other.

11. Propane Conformations: Larger Barrier to Rotation (link)link

12. Butane Conformations (C 2 -C 3 )

13. Gauche Interaction in Butane

14. 2 Different Eclipsed Conformations

15. Strain Energy can be Quantified

16. Butane has Steric and Torsional Strain When Eclipsed

17. PE Diagram for Butane (link)link

19. 1-Chloropropane

20. Saturated Cyclic Compounds

22. Cyclopropane Angle and Torsional Strain

23. Electron Density Map

25. All Dihedral Angles = 0 o

26. Cyclobutane is not Planar

27. Cyclopentane

28. Cyclohexane

29. Chair Conformation link to active site link to active site

30. Boat Conformation

32. How to Draw a Chair Conformation all opposite bonds are parrallel

37. Axial bonds and Equatorial bonds

39. Rings can Flip from one Chair Conformation to Another

40. Flipping Chair Conformations All axial bonds become equatorial All equatorial bonds become axial All “up” bonds stay up All “down” bonds stay down

42. Axial-up becomes Equatorial-up

44. Equatorial Conformation is Preferred (link)link

45. Axial Methyl group is Gauche to C 3 in the ring

46. Gauche Interactions are Flagged by Parallel H’s 1,3-Diaxial Interactions

47. Equatorial Methyl Group is Anti to C 3 in the ring

49. cis 1,3-Dimethylcyclohexane

50. trans 1,3-Dimethylcyclohexane

52. cis 1-Chloro-4-t-butylcyclohexane