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Conformational Analysis of Cyclohexane

Article ID: 41
Last updated: 18 Sep, 2012
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VISIT THE MODELS 360 SITE AT THE CHEMED DL! (search for cyclohexane to get started, is that model a chair?)
 
Conformations of cyclohexane provide a much more complex study on how rotation around C-C bonds can lead to structures with differing potential energies.  Cyclohexane is typically studied in more depth because it is the most common cycloalkane in nature and provides unique stability in its lowest energy state.
 
The most stable conformation is the chair.  The C-C-C bonds are very close to 109.5o, so it is almost free of angle strain. It is also a staggered conformation and so is free of torsional strain.  In this conformation, there are two classes of substituent positions around the chair that explain all 12 hydrogens, axial (six pointing up and down) and equatorial (six pointing horizontally out).  While ignoring the C-H bonds, imagine the chair conformation (see below) as a beach chair, with a back (on the left side) and footrest (on the right side).
 
This conformation is in equilibrium with another chair conformation (see the energy diagram below for both chairs).  Ring flipping interconverts between these chair conformations, and as a result all equatorial substituents on one chair become axial on the other chair and vice versa.  The most stable conformation will always dominate in nature.  Remember, just like ethane or butane, cyclohexanes are constantly in motion.  However, they exist as a chair the majority of the time.  Below is the general structure of the chair.
 
 
 
There are other less stable conformations such as the boat and the twist boat.  These can be considered to be less stable due to the steric interactions between the hydrogens of the molecule or between substituents attached to the cyclohexane.

Draw a chair structure of cyclohexane, including all axial and equatorial hydrogens.

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Organic Chemistry -> Alkanes: Structure and Conformational Analysis -> Conformational Analysis Introduction

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Conformation of Alkanes and Cycloalkanes     Conformational Analysis of Higher Alkanes

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