Properties of atoms in molecules: additivity and transferability of group polarizabilities

Publisher Website
Google Scholar
Abstract
The experimental demonstration of the additivity and transferability of group properties in the hydrocarbons, that is, the establishment of additivity schemes for their molar volumes, polarizabilities and heats of formation, played a central role in establishing the concept of a functional group in chemistry. It is shown here that the theory of atoms in molecules recovers and explains the experimentally observed additivity and transferability of the group polarizabilities in the hydrocarbons, just as has been previously done for the heats of formation, electric moments and molar volumes. All of the group properties exhibit the same pattern of transferable behavior. In particular, the linear relationship between the group polarizabilities and corresponding group volumes, as defined by theory, enable one to predict the mean polarizabilities of hydrocarbons to better than one-half of one percent using readily calculated group volumes. The outer sheath of hydrogen atom charge density polarizes in the direction of the external field, while the carbon atom densities exhibit an opposing polarization. The increase in the longitudinal component of the polarizability tensor with increasing chain length is shown to arise from a field-induced transfer of charge over the length of the molecule. This paper demonstrates that quantum mechanics predicts the properties of an atom in a molecule just as it does those of the molecule itself, even in the presence of an external field.