Bluffton University

Organic Chemistry

Molecular Models:
Conformation and Newman projections
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For unsubstituted cyclohexane, the two chair conformations (or conformers) have the same energy. But when we begin to put substituents on the ring, this quickly comes to a halt: because of axial-axial steric interactions, most substituents prefer to be in an equatorial position. Very large substituents, such as t-butyl groups, lock the ring into a particular conformation!

Examine the models below. Note the steric interactions.

methylcyclohexane
equilibrium tends toward the right
 
t-butylcyclohexane
equilibrium tends toward the right

When more than one substituent is present, the ring will take on whichever conformation is lowest in energy; if possible, all substituents will be in equatorial positions. However, as you will see, this is not always possible in a chair conformation.

Try some exercises in comparing conformations.


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Copyright © 1998, 1999, 2000, 2003, 2007 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.