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ChemOffice.Com - CambridgeSoft

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van der Waals Radius<br />

The van der Waals (VDW) radius is used to specify<br />

the size of atom balls and dot surfaces when<br />

displaying the Ball & Stick, Cylindrical Bonds or<br />

Space Filling models.<br />

The Close Contacts command in the Measurements<br />

submenu of the Structure menu determines close<br />

contacts by comparing the distance between pairs<br />

of non-bonded atoms to the sum of their van der<br />

Waals radii.<br />

The van der Waals radii specified in the Atom<br />

Types table do not affect the results of an MM2<br />

computation. The radii used in MM2 computations<br />

are specified in the MM2 Atom Types table.<br />

NOTE: The space filling model display is set in the Model<br />

Display tab of the Model Settings dialog box. The<br />

appearance of VDW dot surfaces is specified for the entire<br />

model in the Atom Display tab of the Model Settings dialog<br />

box, or for individual atoms using the Right-click Atom<br />

Dots submenu in the Model Explorer.<br />

Text Number (Atom Type)<br />

Text numbers are used to determine which<br />

measurements apply to a given group of atoms in<br />

other parameter tables.<br />

For example, C Alkane has an atom type number<br />

of 1and O Alcohol has an atom type number of 6.<br />

To determine the standard bond length of a bond<br />

between a C Alkane atom and an O Alcohol atom ,<br />

you should look at the 1-6 record in the Bond<br />

Stretching table.<br />

Charge<br />

The charge of an atom type is used when assigning<br />

atom types to atoms in a model.<br />

When the information about an atom is displayed,<br />

the atom symbol is always followed by the charge.<br />

Charges can be fractional. For example, the charge<br />

of a carbon atom in a cyclopentadienyl ring should<br />

be 0.200.<br />

Maximum Ring Size<br />

The maximum ring size field indicates whether the<br />

corresponding atom type should be restricted to<br />

atoms found in rings of a certain size. If this cell is<br />

zero or empty, then this atom type is not restricted.<br />

For example, the maximum ring size of<br />

C Cyclopropane is 3.<br />

Rectification Type<br />

Possible rectification types are:<br />

• D<br />

• H<br />

• H Alcohol<br />

• H Amide<br />

• H Amine<br />

• H Ammonium<br />

• H Carboxyl<br />

• H Enol<br />

• H Guanidine<br />

• H Thiol<br />

NOTE: When you specify a rectification type, the bound-to<br />

type of the rectification type should not conflict with the atom<br />

type. If there is no rectification type for an atom, it is never<br />

rectified.<br />

For example, if the rectification type of O Carboxyl is H<br />

Carboxyl, the bound-to type of H Carboxyl should be either<br />

O Carboxyl or empty. Otherwise, when assigning atom types,<br />

hydrogen atoms bound to O Carboxyl atoms are not assigned<br />

H Carboxyl.<br />

Appendices<br />

<strong>ChemOffice</strong> 2005/Appendix Parameter Tables • 653<br />

Atom Types

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