Understanding Cyclohexane Conformational Analysis
Conformational analysis of cyclohexane involves studying its chair form, axial and equatorial bonds, ring-flipping process, and stability comparison between chair and boat forms. The ring-flipping process interconverts axial and equatorial hydrogens, resulting in a more stable chair conformation. Visual representations aid in grasping the concept of cyclohexane's structural dynamics.
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Conformational Analysis of Cycloalkanes - II Conformational Analysis of Cyclohexane
A three-dimensional model of the chair form of cyclohexane with all H atoms drawn
Three C atoms pucker up and three C atoms pucker down, alternating around the ring. Each C in has two different kinds of hydrogens: (1) axial hydrogens are located above and below the ring (along a perpendicular axis); (2) equatorial hydrogens are located in the plane of the ring (around the equator).
How to Draw a Chair Conformation all opposite bonds are parrallel
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
An important conformational change in cyclohexane involves ring-flipping. Ring-flipping is a two-step process. As a result of a ring flip, the up carbons become down carbons, and the down carbons become up carbons. Axial and equatorial H atoms are also interconverted during a ring-flip. Axial H atoms become equatorial H atoms, and equatorial H atoms become axial H atoms.
Ring-flipping interconverts axial and equatorial hydrogens in cyclohexane The chair forms of cyclohexane are 7 kcal/mol more stable than the boat forms.
The boat conformation is destabilized by torsional strain because the hydrogens on the four carbon atoms in the plane are eclipsed. Additionally, there is steric strain because two hydrogens at either end of the boat, the flag pole hydrogens, are forced close to each other. Two views of the boat conformation of cyclohexane
The chair conformation has no ring strain. All bond angles are 109.5o and all C-H bonds are perfectly staggered
The boat conformation is less stable because of flagpole interactions and tortional strain along the bottom of the boat
The chair and boat conformers are interconvertible at ordinary temperature and cannot be isolated independently
The twist conformation is intermediate in stability between the boat and the chair conformation At room temp, the ratio of chair to boat conformation at equilibrium is 1000:1
Energy Profile for the Chair-Chair Interconversion of Cyclohexane half-chair half-chair boat twist-boat chair twist-boat chair
