THE ROLE OF ONE-PARAMETER PLOTS IN A 2-PARAMETER WORLD

The simplicity of analysis, ease of presentation, and ready extension to new bases (or acids) have led many investigators to choose a one-parameter analysis to interpret physicochemical measurements. Though it is commonly accepted that two factors contribute to donor or acceptor properties, one-parameter correlations often work because much chemistry is dominated by electrostatic interactions. An improved set of enthalpy-based parameters are presented for such analyses as alternatives to donor numbers, Kamlet-Taft β values, and pKbdata. The conditions that must apply in order for a one-parameter analysis to be valid are described, and criteria are offered to indicate when a one-parameter analysis can be misleading. It is shown that an improper estimate of the covalency in a physicochemical measurement relative to that in the basicity scale utilized can lead to deviations in plotted data which could lead an investigator to improperly conclude that steric effects or metal to ligand π-back-bonding exists. © 1990, American Chemical Society. All rights reserved.