It can be seen from Fig. Generally, the polarizability of homologous molecules is positively correlated with the molecular volume , so the electronic spatial extent (<R 2 >) which usually used to represent the electron density volume of a molecule can provide a reasonable explanation for the magnitude of the molecular polarizability. The electronic spatial extent (<R 2 >) and polarizabilities [α iso (∞)] of the C 18 -(CO) n (n = 2, 4, and 6) are collectively plotted in Fig. , from which it can be seen that the polarizabilities of the molecules are almost linearly related to their volumes. Similar conclusion has been found in our recent study on the relationship between the polarizability and molecular volume of various all-carboatomic rings .