Hydrogen bonding. 31. Construction of a scale of solute effective or summation hydrogen‐bond basicity

Abstract

The β scale of solute hydrogen‐bond basicity, formulated from 1:1 hydrogen‐bond complexation constants in tetrachloromethane, has been used to set up a scale of effective or summation hydrogen‐bond basicity, appropriate for the situation in which a solute is surrounded by solvent molecules. The method is based on the equation, where SP is, in this work, a set of solute water–solvent partition coefficients in a given system. The explanatory variables are solute parameters as follows: R2 is an excess molar refraction, π is the solute dipolarity/polarizability, Σα and Σβ 2 are the effective solute hydrogen‐bond acidity and basicity and Vx is McGowan's characteristic volume. Various equations are established using β in the equation, and then amended β values are back‐calculated and new Σβ values obtained. It is found that for most solutes, the effective basicity Σβ is invariant over the systems used to within an experimental error of around 0·03 units. About 350 Σβ values obtained from two or more experimental log P values are listed, together with values for homologous series and a number of singly determined values. For some specific solutes, such as sulphoxides, alkylanilines and alkylpyridines, Σβ 2 is not constant, and an additional solute basicity denoted as Σβ is needed in order to deal with partitions from water to solvents that are partially miscible with water, such as isobutanol and octanol. Values of Σβ, and where possible Σβ also, are listed for 80 additional solutes.