Basics of Conformational Analysis

 Conformational analysis means judging or calculating the relative energies of the various stereoisomers related by rotation around single bonds. Various computer programs are available that will do this more or less automatically given input of one or more of the conformations. The conformational methodology is called molecular mechanics, since it treats the molecules as mechanical systems consisting of relatively impenetrable atomic balls connected by springs of various lengths and strengths.

Here is how molecular mechanics works. In doing analyses "by hand", these are the factors that must be considered. In such cases, we approximate force fields by using a few simple parameters derived from analysis of small molecules.

For simple acyclics like butane, or cyclics like cyclohexane, one should be able to make useful estimates of energy differences.

Here is an analysis of butane.

And here is such an analysis for the conformers of the dimethylcyclohexanes, using as the only required parameter the energy difference between the two principal conformers of butane, 0.8 kcal/mol.

Build models and make sure you can find the interactions that are described, and recognize the chirality of some of these species.

This page last modified 12:24 PM on Tuesday August 16th, 2011.
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