Ring perception methods

There are many algorithms implementing the SSSR ring perception. They are mostly based on graph theory (see Graph Theory in Chemistry) and implement more or less the methods used in tree traversals and tree searching. 

Underlying most ring perception algorithms there are just a few basic perception methods and operations, most of... 

Ring perception is important for the analysis and description of chemical structure ring systems. There are a wide variety of rings sets and perception methods to choose from, many of which are specifically aimed at particular applications. Certain generalizations can be made, however, to give an indication of the best general purpose sets and methods. 

Three steps have been most important in the development of the COSMOfrag method. The first was the development of a molecular perception routine, which analyzes a molecule with respect to the hybridization states of atoms, bond orders, rings, and ring properties like aromaticity, and even their stereochemical... 

Multiple bonds, internal rings, and other molecular substructures or subgraphs (see Figure 4.10a) are recognized through a circular inspection method. A circle of inspection centered on each detected atom is considered (see Figure 4.10b). Unknown border pixels found in this way are kept and used as the initial point for a new counterclockwise contour search, and the perception of new vertices and probable new atoms is carried out as described earlier. 

It is assumed that ring information is available to the SDG program its perception is not discussed here. Three nonexclusive methods have been used to assign coordinates to ring systems (RSs) ... 

The SSSR is a fundamental basis containing the fx smallest simple-cycles in a structure. The majority of non-chemical and many chemical applications use the SSSR as the ring set since fx can be calculated easily and the mathematical foundations of a fundamental basis are well understood. The SSSR is still the most important and widely used of all ring sets. As with the set of all cycles, algorithms exist that use each of the methods outlined in Section 3. Since the 1989 review, five improved SSSR perception algorithms for chemical structure applications have been published. ... 

---