HYDROGEN-BONDING .31. CONSTRUCTION OF A SCALE OF SOLUTE EFFECTIVE OR SUMMATION HYDROGEN-BOND BASICITY

The 'beta2H' 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, log SP = c + rR2 + spi2H + aSIGMAalpha2H + bSIGMAbeta2 + upsilonVx 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, pi2H is the solute dipolarity/polarizability, SIGMAalpha2H and SIGMAbeta2 are the effective solute hydrogen-bond acidity and basicity and Vx is McGowan's characteristic volume. Various equations are established using beta2H in the equation, and then amended beta2H values are back-calculated and new SIGMAbeta2H values obtained. It is found that for most solutes, the effective basicity SIGMAbeta2H is invariant over the systems used to within an experimental error of around 0.03 units. About 350 SIGMAbeta2H 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, SIGMAbeta2 is not constant, and an additional solute basicity denoted as SIGMAbeta2O 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 SIGMAbeta2o, and where possible SIGMAbeta2H also, are listed for 80 additional solutes.