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The allyl radical, CH 2 =CHCH 2·, is a textbook
example of resonance-enhanced stabilization:
6. Also in the Theory tab, set the Spin Multiplicity
to 2.
Administrator
H 2 C
H
C
To examine Radicals with Spin Density surfaces:
1. From the File menu, choose New.
2. Type 1-propene in the ChemDraw
Name=Struct text box.
A molecule of 1-propene appears.
Create a radical:
CH 2
H 2 C
1. Select the H9 hydrogen.
2. Press Delete.
A dialog box appears asking if you want to turn
off rectification. Chem3D is chemically
intelligent, and knows that in most cases
carbon atoms have four substituents. Radicals
are one of the rare exceptions.
3. Click Turn Off Automatic Rectification.
The propene radical is displayed.
H
C
CH 2
NOTE: If you are doing this tutorial with CSMOPAC,
there is no Spin Multiplicity setting.
This molecule is intended to be a radical, and setting
the Spin Multiplicity ensures that it is.
One of the best ways to view spin density is by
mapping it onto the Total Charge Density surface.
This allows you to see what portions of the total
charge are contributed by unpaired electrons, or
radicals.
To view Spin Density mapped onto Total Charge
Density Surface:
1. In the Properties tab, select Molecular Surfaces
and Spin Density (use Shift-click).
2. Press Run.
The calculation toolbar appears.
When the calculation is finished, select the
Trackball tool and rotate the model back and forth.
It should be completely planar.
4. From the Calculations menu, point to
Gaussian, and choose Minimize Energy.
5. In the Theory tab, set the Method to PM3, and
the Wave Function to Open Shell (Unrestricted).
46 •Chem3D Tutorials CambridgeSoft
Tutorial 9: Mapping Properties onto Surfaces