Chemical graph theory is a field of mathematical chemistry that describes physico chemical properties of alkanes. In chemical compounds, atoms represent the nodes and chemical bonds represent the edges. Graph theory is used to define topological indices that can provide information about molecular size, shape, symmetry and reactivity. Quantitative structure–activity relationship (QSAR) and (QSPR) Quantitaive structure–property relationship studies are graph based descriptor used to correlate chemical structure to biological activity. In quantum chemistry, Schrodinger equation is to determine the electronic structure of molecules. In graph theory, adjacency matrix and the connectivity of atoms in the molecule play an important role. In molecular orbital theory, the wave functions representing molecular orbitals are often described using linear combinations of atomic orbitals. These linear combinations can combinations are represented by edges in graph theory language. Graph algorithms are applied to study the electronic properties of molecules, to predict reactivity, and optimize molecular structures. Huckel molecular orbital theory is a graph based method used to estimate the electronic structure of conjugated hydrocarbon systems. The electron density distribution in a molecule can be visualized as an electron density graph, where nodes represent atomic positions and edges describe the distribution of electrons between atoms.