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Administrator<br />

Clean Up Structure or MM2 computation alters<br />

these values. To use values you set in these<br />

computations, you must apply a constraint.<br />

Setting Bond Lengths<br />

To set the length of a bond between two bonded<br />

atoms:<br />

1. Select two adjacent atoms.<br />

2. From the Structure menu, point to Measurement<br />

and choose Set Bond Length Measurement.<br />

The Measurements table appears, displaying<br />

distance between the two atoms. The Actual<br />

value is highlighted.<br />

3. Edit the highlighted text.<br />

4. Press the Enter key.<br />

Setting Bond Angles<br />

To set a bond angle:<br />

1. Select three contiguous atoms for a bond angle.<br />

2. From the Structure menu, point to Measurement<br />

and choose Set Bond Angle Measurement.<br />

The Measurements table appears, displaying<br />

the angle value. The Actual value is highlighted.<br />

3. Edit the highlighted text.<br />

4. Press the Enter key.<br />

Setting Dihedral Angles<br />

To set a dihedral angle:<br />

1. Select four contiguous atoms.<br />

2. From the Structure menu, point to Measurement<br />

and choose Set Dihedral Measurement.<br />

The Measurements table appears, displaying<br />

the angle value. The Actual value is highlighted.<br />

3. Edit the highlighted text.<br />

4. Press the Enter key.<br />

Setting Non-Bonded<br />

Distances (Atom Pairs)<br />

To set the distance between two non-bonded atoms<br />

(an atom pair):<br />

1. Select two unbonded atoms.<br />

2. From the Structure menu, point to Measurement<br />

and choose Set Distance Measurement.<br />

The Measurements table appears, displaying<br />

the distance. The Actual value is highlighted.<br />

3. Edit the highlighted text.<br />

4. Press the Enter key.<br />

Atom Movement When<br />

Setting Measurements<br />

When you change the value of a measurement, the<br />

last atom selected moves. Chem3D determines<br />

which other atoms in the same fragment also move<br />

by repositioning the atoms that are attached to the<br />

moving atom and excluding the atoms that are<br />

attached to the other selected atoms.<br />

If all of the atoms in a measurement are within a<br />

ring, the set of moving atoms is generated as<br />

follows:<br />

• Only one selected end atom that describes the<br />

measurement moves while other atoms<br />

describing the measurement remain in the<br />

same position.<br />

• If you are setting a bond length or the distance<br />

between two atoms, all atoms bonded to the<br />

non-moving selected atom do not move. This<br />

set of non-moving atoms is extended through<br />

all bonds. From among the remaining atoms,<br />

any atoms which are bonded to the moving<br />

atom move; this set of moving atoms is also<br />

extended through all bonds.<br />

64 •Building and Editing Models <strong>CambridgeSoft</strong><br />

Setting Measurements

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