When a molecule's atoms and bonds are specified, it may be that there are cycles in the graph. Atoms that are connected via ring bonds are ring atoms . The algorithms used for these tasks are beyond the scope of this document. However, we will point out that of the two tasks above, the first is relatively trivial and the second is surprisingly complex. Bond type, bond order, and aromaticity Bonds are, in a sense, both an explicit and a derived property.
Bond order is a formal property .
The Daylight system uses an extended version of Hueckel's rule to identify aromatic molecules and ions. Note that the definition of aromaticity is not intended to imply anything about the reactivity, magnetic resonance spectra, heat of formation, or odor of substances. Because the Daylight system represents molecules as graphs with chiral information, the possible symmetry groups are those from two dimensional rotations. A canonical labeling of a graph depends only on the graph itself, not its history. Programmers using the Daylight Toolkit can access the canonical labelling directly.