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b. From the Structure menu, point to
Measurement, and then choose Bond Angles.
NOTE: If the Measurements table appears along side
the Model Explorer, you can stack the windows by
locking the Model Explorer window open and dragging
the Measurements table on top of it.
The information you chose appears in the
Measurements table. The measurements in the
Actual and Optimal columns are nearly
identical. The Actual column represents the
measurements for the model in the active
window. The Optimal measurements (for bond
lengths and bond angles only) represent the
standard measurements in the Bond Stretching
and Angle Bending parameter tables.
Rotate the orientation of the model to obtain a
Newman projection (viewing the model along a
bond.) This orientation helps clarify the
conformations of ethane.
To rotate a methyl group on an ethane model:
1. Click the Trackball tool .
When you mouse over the edges of the model
window, the Rotation Bars appear.
Only the X- and Y-rotation bars are active.
These Rotations bars are always active because
they are not dependent on any atoms being
selected.
2. Click the X-Axis rotation bar and drag to the
right.
As you drag, the status bar shows details about
the rotation.
3. Stop dragging when you have an end-on view
of ethane.
This staggered conformation, where the
hydrogens on adjoining carbons are a
maximum distance from one another (which
represents the global minimum on a potential
energy plot) represents the most stable
conformation of ethane.
Chem3D shows the most common conformation
of a molecule. You can rotate parts of a molecule,
such as a methyl group, to see other conformations.
36 •Chem3D Tutorials CambridgeSoft
Tutorial 4: Examining Conformations