Butane torsional profile

However, energies are just as crucia 1, and these are sometimes harder to come by. For hydrocarbons and simpler organics, there is a large database of heats of formation, and, hence, strain energies, and these are valuable in parameterization. Other energies include rotation barriers and conformational differences. A competent force field should reproduce the butane torsional profile of Figure 2.6, and should obtain the A values for many cyclohexane substituents. Due to the similarity to real molecular vibrational modes, IR vibrations should be a valuable source for a force field, but in practice few modern force fields use them in their parameterization. 

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