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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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Presentation Transcript
Conformational analysis

Conformational Analysis

Newman Projections

Ring Strain

Cyclohexane Conformations





Definitions
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).


60 o rotation causes torsional or eclipsing strain
60o Rotation Causes Torsional or Eclipsing Strain


Types of strain
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


Definitions1
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.


Propane conformations larger barrier to rotation link
Propane Conformations: Larger Barrier to Rotation (link)






Butane has steric and torsional strain when eclipsed
Butane has Steric and Torsional Strain When Eclipsed





Cyclopropane angle and torsional strain
CyclopropaneAngle and Torsional Strain







Chair conformation link to active site
Chair Conformation link to active site



How to draw a chair conformation all opposite bonds are parrallel
How to Draw a Chair Conformationall opposite bonds are parrallel


Axial bonds and equatorial bonds
Axial bonds and Equatorial bonds



Flipping chair conformations
Flipping Chair Conformations

  • All axial bonds become equatorial

  • All equatorial bonds become axial

  • All “up” bonds stay up

  • All “down” bonds stay down


Axial up becomes equatorial up
Axial-up becomes Equatorial-up



Axial methyl group is gauche to c 3 in the ring
Axial Methyl group is Gauche to C3 in the ring



Equatorial methyl group is anti to c 3 in the ring
Equatorial Methyl Group is Anti to C3 in the ring


Cis 1 3 dimethylcyclohexane
cis 1,3-Dimethylcyclohexane


Trans 1 3 dimethylcyclohexane
trans 1,3-Dimethylcyclohexane


Cis 1 chloro 4 t butylcyclohexane
cis 1-Chloro-4-t-butylcyclohexane


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