The atomic ionicity index in a molecule has been defined and the model of ^13C NMR chemical shifts of alkanes has been studied with the atomic ionicity index (INI), polarizability effect index (PEI) and the structural information parameters N^i~H(i=αβΥ). The results indicate that the ^13C NMR chemical shifts of alkanes can be described as follows: CS= 194.6156-37.7394(INI)+98.6505(ΣPEI)+27. 1630(INI/ΣPEI)- 652.9106(ΣPEI/INI)+0.7735N^ α~H+2.2468N^β~H- 0. 1742N^γ~H. The chemical shifts of 304 carbon atoms are predicted with the standard error being only 0.9860δ and the average absolute error 0.77 δ. The calculated values are well consistent with the observed ones.

Key words: POLARIZATION EFFECT, ALKANE, QUANTITATIVE EQUATION, CARBON-13 NMR SPECTROMETRY, CHEMICAL SHIFT