M Razinger | Search PubMed

PubMedDate not supplied

Graph automorphism perception algorithms in computer-enhanced structure elucidation.

The concept of graph symmetry is explained in terms of the vertex automorphism group, which is a subgroup of the complete vertex permutation group. The automorphism group can be deduced from the automorphism partition of graph vertices. An algorithm is described which constructs the automorphism group of a graph from the automorphism vertex partitioning. The algorithm is useful especially for graphs which contain more than one vertex-partition set. Several well-known topological symmetry perception algorithms that yield automorphism partitions are compared. The comparison is favorable to the Shelley-Munk algorithm, developed in the framework of the SESAMI system for computer-enhanced structure elucidation.

Algorithms↗

PubMedDate not supplied

Stereoisomer generation in computer-enhanced structure elucidation.

The existence of stereoisomerism can be related to the presence of structural features referred to as stereocenters. On the basis of this relationship, computer software capable of generating all stereoisomers of a given constitutional isomer has been developed. Input to the program is a canonical connection table. In an initial step the stereocenters present in the structure are identified and characterized either as true-stereocenters or para-stereocenters. In the presence of n different true-stereocenters, structure generation is trivial and leads to 2n stereoisomers, each of which can be represented by a parity vector. In the presence of topological symmetry, the number of stereoisomers may be less than 2n; i.e., some of the 2n parity vectors correspond to equivalent configurations. An algorithm for determining equivalences among the set of 2n parity vectors is described. Program output includes the parity vector of each valid stereoisomer and the relationship between them, i.e., enantiomeric or diastereomeric. A simple procedure for representing the parity vector of the stereoisomer as a three-dimensional representation is given.

Chemistry, Organic↗