Grey dotted lines indicate pi-bonding. Rules are applied systematically using bond lengths, angles and torsion angles. The method tolerates missing hydrogen atoms. Standard patterns are assigned following CSD database conventions e.g. a perchlorate group has three double bonds, one single bond, and a single negative charge on that single-bonded oxygen. Full details are beyond the scope of this User Guide , but in general the process is highly successful for organic structures.
Some ambiguities can arise with de-localised charge systems, and with some metal complexes.
Iteratively undoes each separate stage of edits. The most recent 200 edits for one structure are stored by PreQuest and each can be undone until no more steps are available. Moving to another structure removes the ability to undo edits to a previous structure. Iteratively re-applies the edits that have been undone using the UNDO function. This feature is under development for the handling of catena-structures.