Are Chromatographic Retention Indices Shape Dependent

We would like to critically examine the interpretation of the regression equation (2) that it supports a notion that the Chromatographic retention index for benzenoids is shape dependent. As one can see from equation (1), most of the correlation between the structure and the Chromatographic retention index as the property is described by the connectivity index that is bond additive and size dependent. The conclusion therefore ought to be that the Chromatographic retention values are mostly bond additive and size dependent. Because of this pronounced bond-additivity, clearly we can understand why indices that are global are inferior in this particular application. 

Are the Chromatographic retention indices not shape dependent It appears that the retention indices of benzenoids should not be viewed as a shape-dependent property, despite the fact that the regressions of the Chromatographic indices were improved by the use of L/B. We can justify this claim by comparing the regressions using molecular descriptors that characterize better molecular shape than L/B. If the 

In the former only the carbon atoms on the molecular periphery contribute in the construction of the average interatomic distances and the average powers of the distances. For cata-condensed benzenoids, both and S are identical, but for peri-condensed benzenoids there is a difference between the two sets of descriptors. When we use 5 descriptors in the regressions of the Chromatographic retention indices we obtain  

A comparison with the corresponding values of equations (3)-(5) shows that the descriptors D, D, D, in which the atoms in the interior as well as those at the periphery contribute, are superior in describing Chromatographic indices of benzenoids. The superiority of over 5 descriptors becomes even more pronounced if we limit the analysis only to peri-condensed benzenoids for which the descriptors D and differ. In Table 27 we compare the regressions using the shape descriptors and the full descriptors 

We have to conclude that the Chromatographic retention index for planar benzenoids is inherently not a shape-dependent property, i.e., it is not a property that will be determined solely by the atoms on the molecular periphery. One may wonder Why 

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