Özet:

Topological indices have important role in theoretical chemistry for QSPR researches. Among the all topological indices the Randić index has been used more considerably than any other topological indices in chemical and mathematical literature. Most of the topological indices as in the Randić index are based on the degrees of the vertices of a connected graph. Recently novel two degree concepts have been defined in graph theory; ev-degrees and ve-degrees. In this study ev-degree Randić index is defined by using ev-degree concept as parallel to their corresponding classical degree version. This new ev-degree Randić index is compared with the Randić index by modelling some physicochemical properties of octane isomers. It is showed that the ev-degree Randić index give better correlation than the Randić index to predict the entropy, acentric factor and  standard enthalpy of vaporization of octanes.  Also the exact values of the ev-degree Randić index for the well-known graph classes such as; paths, cycles, stars and complete graphs are given.

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