All searches, except Name Search, can be restricted by a set of constraints. The Dialog windows of these searches contain a panel with a radio button for activating constraints and a button for editing search constraints. When you press the Edit button a dialog box will appear that allows you to search selected libraries for matches with a set of specific criteria. Four constraint types are available: Molecular Mass range, Number of Atoms range, Allowed Elements and Good-Bad list. Searches conducted with activated constraints can be time consuming because each library entry is examined to find those that match the criteria you have set. The Search Constraints are especially useful when you are dealing with large libraries and you want to retrieve hits that are of interest for your specific problem.

The Good list (required substructures) allows you to focus your search results on the particular compound classes you are most interested in. The Bad list (forbidden substructures) eliminates from a hit list all structures containing unwanted functional groups. For example the Good-Bad List can be used in a search of acids with a specific molecular formula, or you can search for spectra similar to an unknown, with the requirement that ketones may not appear in the hit list. The figure below shows a Structure Constraints dialog window set for C, N, and O as allowed elements. The Good-Bad list is set for esters as required (good) and for tetriary amines as a forbidden (bad) functional group.