In this paper, the relationship between the isomerization of the aliphatic alkane molecules and the thermodynamic properties is studied. Using the molecular graph theory, AN index, which is able to describe the molecular branching, has been proposed. Based on this index, equations in an unified form for calculating data of various thermodynamic properties of the saturated hydrocarbons (e.g., boiling points, densities, chromatographic retention indices, enthalpies of formation, heats of atomization and refractivities) have been obtained.

Key words: THERMODYNAMIC PROPERTIES, ALKANE, STRUCTURE AND PROPERTY CORRELATION, ISOMERIZATION REACTION, GRAPH-THEORETICAL ALGORITHMS, BRANCHING