Abstract: Systematic studies were made on graph theory in quantitative structure-activity/property relationships (QSAR/QSPR). Here Quantitative Molecular Modelling (QMM) was done on quantitative structure-spectrum relationship (QSSR) studies. The regularity of chemical shift sum (CSS) for ¹³C NMR in 65 alkanes was modelled and/or predicted by using a set of novel chemical graph indices, called molecular topological subgraph index vector (VMSG). The newly developed SGI descriptors with R>0.95 as an equation of multiple variables:CSS=b_qg_q=b ^*g=-35. 266+29. 219g₁+37. 493g₂+20. 707g₃+30. 015g₄+37. 547g₅+88. 378g₆+49. 369 g₇+92. 211g₈+41. 276g₉+63. 070g₁₀, n=65, R=0. 9901, SD=8. 9466, F=268. 34, U=214779. 00, Q=4322. 2188; CV:n=65, R²=0. 9587, SD=12. 9468, F=125. 31, where q=1 to 10(I, E, 2M, 3M, 4M, 3E, 4P, 4iP, 4tB, 3Dm), g ave good results.

Key words: Quantitative structure-activity/property/spectrum relationships (QSAR/QSPR/QSSR), Quantitative molecular modelling (QMM), Chemical shift sum (CSS), ¹³C NMR, Alkanes, Integrator molecular topological subgraph vector (VMSG,g)