ChemOffice.Com - CambridgeSoft

Administrator
In the Measurements table, notice that the dihedral
for H(3)-C(1)-C(2)-H(8) is now minus 0 degrees, as
shown in the model.
To compute steric energy:
Tutorial 5: Mapping
Conformations with
the Dihedral Driver
The dihedral driver allows you to map the
conformational space of a model by varying one or
two dihedral angles. At each dihedral angle value,
the model is energy minimized using the MM2
force field and the steric energy of the model is
computed and graphed. After the computation is
complete you can view the data to locate the models
with the lowest steric energy values and use these as
starting points for further refinement in locating a
stationery point.
1. From the Calculations menu, point to MM2,
then choose Compute Properties.
NOTE: The property tab defaults should remain as
in the previous calculation.
2. Click Run.
The final line in the Output box appears as follows:
NOTE: The values of the energy terms can vary slightly
based on the type of processor used to calculate them.
The steric energy for the eclipsed conformation
(~3.9 kcal/mole) is greater in energy than that of
the staggered conformation (~1 kcal/mole),
indicating that the staggered configuration is the
conformation that is more likely to exist.
To use the dihedral driver:
1. Select the bond in your model that defines the
dihedral angle of interest.
2. Choose Dihedral Driver from the Calculations
menu.
The Dihedral Driver window opens. When the
computation is completed, a graph is displayed
showing the energy (kcal) vs. theta (angle of
rotation).
To view the conformation at any given point:
1. Point to a location (specific degree or energy
setting) inside the Dihedral Driver Window.
A dashed-line box appears. As you move the
mouse, the box moves to define a specific
point on the graph.
NOTE: As a rule, steric energy values should only be used
for comparing different conformations of the same model.
2. Click on the point of interest.
38 •Chem3D Tutorials CambridgeSoft
Tutorial 5: Mapping Conformations with the Dihedral Driver