The nature of topological parameters. II. The composition of topological parameters.

The composition of thirty topological parameters of various types including the chi, kappa and tau parameters and the Wiener indices was determined. Those derived from alkyl and substituted alkyl groups are a function of branching and steric effects; those derived from haloalkanes and haloalkenes are a function of some combination of polarizability, dipole moment, the number of halogen atoms of each type, and the ration of the number of branches to the number of atoms in the longest chain. It follows that topological parameters are actually counts of the number of atoms of each type, bonds of each type, valence, nonbonding and core electrons, branches at each position, OH and NH bonds, and nonbonding electron pairs on O and/or N atoms. These counts can be related to polarizability, dipole moment, hydrogen bonding, and steric effects, which are the true determinants of properties and biological activities. Topological parameters themselves do not have a cause and effect relationship with the quantities they are used to model. They function because: 1. They are counts of quantities that are related to the fundamental quantities that determine properties. 2. They are composite parameters which for the purpose of obtaining a predictive empirical relationship are able to represent a data set as well as pure parameters.