ON USING GRAPH-EQUIVALENT CLASSES FOR THE STRUCTURE ELUCIDATION OF LARGE MOLECULES

This paper presents a new algorithm to enumerate the isomers of organic compounds. The method is based on the concept of equivalent classes which is now largely used in computational chemistry. The utilization of the equivalent classes enables the elucidation of molecules containing a large number of atoms in a realistic computational time. The main problem during the isomer-generation process is to avoid the presence of redundant structures. The number of identical structures can be enormous, and the process by which two structures are compared is time consuming. We show how with the equivalent classes it is possible to reduce the number of comparisons and reduce the complexity of the isomorphism check function. Exhaustivity and irredundancy of our generator are examined by using graph theory. This technique has been employed with success in the real world of structure elucidation. Results for lignin and coal structures are presented.