Based on characteristics and connectivity of the groups in molecules, the group bonds can be got to describe the molecular structure. A kind of group bond was a chemical bond with two groups, therefore the group bonds contained the property information of and connectivity information of the groups in molecules. Group bonds can be got directly from molecular structure, and can be used to calculate the property of molecules. A new method, the group contribution method, was developed that can be used to calculate the refractive index of alkanes and cycloalkanes from molecular structure. The calculated results showed that the calculated refractive indexes of alkanes and cycloalkanes using the group bond contribution method were in good agreement with the experimental data, the mean relative deviation was 0.11% for 950 alkanes and cycloalkanes, and the group bond contribution method had advantages over the group contribution method and chemical bond contribution method.

Key words: ALKANE, CYCLOALKANE, STRUCTURE AND PROPERTY CORRELATION, MOLECULAR STRUCTURE, REFRACTIVE INDEX