Hydrogen bonding acceptor strength

Despite the availability of numerous computer algorithms for logP0/w calculations, it is useful to consider qualitatively that the most significant molecular parameters that affect logPe/w have been noted by Tamlet et al. to be size, polarity/polarizability, and hydrogen bond acceptor strength [46]. 

Note that the field effect, F, and Hammett sigma values can only be related to the loss of hydrogen bond acceptor strength, e(5. As noted by Taft (1996) the relationship between ea and aqueous pKa is poor, but log P-octanol is unaffected by solute ea. 

This interpretation is also supported by the results of a study correlating the observed diastereomeric excess with the Kamlet-Taft (3 parameter [29], a measure of the hydrogen-bond acceptor strength. A linear free energy relationship was found to exist between P and the diastereomeric excess for those solvents having a (hydrogen bond donor strength) = 0 [28],... 

V is a solute volume term t represents the solute polarizability j8h and a, are measures of hydrogen bond acceptor strength and... 

TABLE 16. Hydrogen-bonding acceptor strengths of neutral bases... 

It must be recalled that y3(OH) is a solvent scale and that solvent and solute scales of hydrogen-bond acceptor strength are not entirely equivalent. For example, for 23 common bases, jS(OH) explains only 91% of the variance of a solute scale constructed [12] with the same property, the hydrogen-bond shift of the same n n transition of 4-nitrophenol, but in the solvent CCI3CH3 instead of the pure base. 

Laurence, C., Berthelot, M., Evain, K. and Illien, B. (2005) The pAThb scales and enthalpies of the hydrogen bond acceptor strength of thioethers, thiols, and disulfides. Can. J. Chem., 83, 138-145. 

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