The Structural Properties Section includes those properties that are in some way characterizations of the chemical's molecular structure. The section currently contains two fields:

The Abbreviations Dialog shows the definitions of all the abbreviations used in Cranium and Synapse. To activate the dialog, select the Help menu's Abbreviations command. See here for documentation.

The symmetry number is defined as the number of identical configurations of a molecule's structure which can be arrived at by rigid rotations. For example consider the molecular structure of propane. The two end methyl groups can freely rotate assuming three identical configurations. The entire molecule itself can pivot around the central carbon giving two identical configurations. Multiplying the number of identical configurations together gives us a symmetry number of 18.

Optical isomers arise from the presence of asymmetric carbon atoms. The number of optical isomers is needed by some techniques which estimate the absolute entropy.

The values shown below are the Symmetry Number and the Number of Optical Isomers for 1,3,5-trimethylbenzene:

Number of Optical Isomers = 1 Symmetry Number = 162

Each field contains a label, a datum control, an estimates control, and a units control.

1	Datum Control displays the field's physical property's data value.
2	Estimate Control: displays the field's physical property's estimated value.
3	Units Control: displays the current units for the field's physical property. The Units Controls are disabled because both properties are dimensionless.

Both properties, the symmetry number and the number of optical isomers, are integers. They are edited in the same manner as other fields, except that the application will only allow you to enter integer values.

Entering a value of 1 for either property is theoretically equivalent to not entering any value. In essence a value of 1 indicates the structure has no symmetry or no optical isomers. However, estimation techniques may handle these two situations differently. If an estimation technique needs a symmetry number value, the lack of the value may cause the technique to fail. We thus recommend adding a value of 1 when structures have no symmetry or no optical isomers.

Both the symmetry number and number of optical isomers fields are edited using the Datum-Reference edit Dialog. (See here for documentation.)

A green triangle in the data control's upper right corner indicates that additional data are available. (See documentation on the Datum-Reference All Data Dialog for details on managing data having different status.)

Clicking the right mouse button within a field's datum control activates the field's datum commands menu.

The menu's commands enable you to copy values, clear values and manage the property's estimation techniques. See Common Menu Commands for documentation on the commands commonly found on command menus. See below for documentation on this field's specific menu commands.

• Edit All Data: uses the All Data dialog to enable editing data having status values of passive, rejected or unknown. See the Datum-Reference All Data Dialog for documentation.)
• Edit Data: enables you to view and mofidy the current physical property's datum. The property value, accuracy, reference and comments can be viewed and edited. See Datum Edit Dialog for documentation.

  Each property field runs a set of verification tests to check the validity of an entered value. Specifically:

  • Symmetry Number (Sym #): value must be an integer greater than 0
  • Number of Optical Isomers (Opt Iso): value must be an integer greater than 0
  Cranium or Synapse will signal an error if the entered value fails a physical property verification test.

The Estimation Details dialog shows the estimated value, the technique used to generate the estimate, and any comments generated during the estimation. The dialog also has two buttons to provide more information about the technique used to generate the estimate:

• Tech Notes: displays the general notes associated with the estimation technique.
• Tech Ref: display the document associated with the technique's reference.

The Estimates column of each field displays the physical property's estimated value. Clicking the right mouse button on the estimate control displays the command menu.

The menu's commands enable you to copy, cut and clear values from the estimate control. (You cannot paste a value into an estimate control.) See Common Menu Commands for documentation on the commands commonly found on command menus. Some of this field's more specific commands are:

• Compute Estimate: activates the Property Estimation dialog which enables you to estimate the current physical property. The functionality of this command is similar to that of the Commands menu Compute Estimates command. The key difference is that the estimates control's menu command limits the estimation to only the current physical property. See Estimating Chemical Properties for additional documentation.
• Select Technique: enables you to specify the estimation mode and the estimation technique used to estimate the current physical property. Selecting this command activates the Estimation Technique Information dialog.

  The dialog lists two estimation modes: Automatic and Manual. By default all estimations are initially set to Automatic Mode. Once you choose Manual Mode, the list of estimation techniques is enabled allowing you to choose any application estimation technique. See documentation on Manual Techniques Dialog for details about manually selecting estimation techniques.

Both the symmetry number and the number of optical isomers are dimensionless so their fields' units controls are not enabled.

Topic	Description
Estimating Chemical Properties	a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
Getting Started using Cranium	provides a quick tour of Cranium's capabilities including a discussion of structure editing.
Chemicals Chapter	the chemicals chapter contains numerous sections for entering and displaying data and estimates including the chemical structure section.