Abstract
A large number of drug experiments revealed that there exists strong inherent relation between the drugs molecular structures and the bio-medical and pharmacology characteristics. Due to the effectiveness for pharmaceutical and medical scientists of their ability to grasp the biological and chemical characteristics of new drugs, forgotten topological index was defined to analyze the drug molecular structures. This index is applicable for testing the chemical and pharmacological properties of drug molecular structures that can make up for lack of chemical experiments and can provide a theoretical basis for the manufacturing of drugs which is widely welcomed in developing areas. In this paper, based on the drug molecular structure analysis and vertex dividing technique with respect to their degrees, we present the forgotten topological index of the line graphs of several popular chemical structures which is quite common in drug molecular graphs.