Conformational Analysis - La Salle University

Conformational Analysis - La Salle University

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.

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). 60o Rotation Causes Torsional

or Eclipsing 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

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. Potential Energy Diagram

Propane Conformations: Larger Barrier to Rotation (link)

Butane Conformations (C2-C3)

Gauche Interaction in Butane 2 Different Eclipsed

Conformations Strain Energy can be Quantified

Butane has Steric and Torsional Strain When Eclipsed

PE Diagram for Butane (link)

1-Chloropropane Saturated Cyclic Compounds

Cyclopropane Angle and Torsional Strain

Electron Density Map

All Dihedral Angles = 0 o

Cyclobutane is not Planar

Cyclopentane Cyclohexane

Chair Conformation link to active site

Boat Conformation

How to Draw a Chair Conformation all opposite bonds

are parrallel Axial bonds and

Equatorial bonds Rings can Flip from one Chair

Conformation to Another 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

eq. up Axial-up becomes Equatorial-up

Equatorial Conformation is Preferred (link)

Axial Methyl group is Gauche to C3 in the ring

Gauche Interactions are Flagged by Parallel Hs

1,3-Diaxial Interactions Equatorial Methyl Group is Anti

to C3 in the ring cis 1,3-Dimethylcyclohexane

trans 1,3-Dimethylcyclohexane

cis 1-Chloro-4-t-butylcyclohexane

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