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Conformational Analysis

Conformational Analysis. Newman Projections Ring Strain Cyclohexane Conformations. Views of Ethane. The Newman Projection. Rotational Conformations of Ethane. Definitions. Conformations - Different spatial arrangments that a molecule can adopt due to rotation about sigma bonds.

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Conformational Analysis

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  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 (60o dihedral angle), maximizing the separation. • Eclipsed - A high energy conformation where the bonds on adjacent atoms are aligned with each other (0o dihedral angle).

  6. 60o 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 180o with respect to each other. • Syn - Description given to two substitutents attached to adjacent atoms when their bonds are at 0o with respect to each other. • Gauche - Description given to two substitutents attached to adjacent atoms when their bonds are at 60o with respect to each other.

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

  10. Butane Conformations (C2-C3)

  11. Gauche Interaction in Butane

  12. 2 Different Eclipsed Conformations

  13. Strain Energy can be Quantified

  14. Butane has Steric and Torsional Strain When Eclipsed

  15. PE Diagram for Butane (link)

  16. 1-Chloropropane

  17. Saturated Cyclic Compounds

  18. CyclopropaneAngle and Torsional Strain

  19. Electron Density Map

  20. All Dihedral Angles = 0o

  21. Cyclobutane is not Planar

  22. Cyclopentane

  23. Cyclohexane

  24. Chair Conformation link to active site

  25. Boat Conformation

  26. How to Draw a Chair Conformationall opposite bonds are parrallel

  27. Axial bonds and Equatorial bonds

  28. Rings can Flip from one Chair Conformation to Another

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

  30. Axial-up becomes Equatorial-up

  31. Equatorial Conformation is Preferred (link)

  32. Axial Methyl group is Gauche to C3 in the ring

  33. Gauche Interactions are Flagged by Parallel H’s1,3-Diaxial Interactions

  34. Equatorial Methyl Group is Anti to C3 in the ring

  35. cis 1,3-Dimethylcyclohexane

  36. trans 1,3-Dimethylcyclohexane

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