H-bond donor acidity

Fig. 4. Phase parameters (regression coefficients) for hydrophobicity (t)), n- and rc-electron activity (r), H-bond donor acidity (b), H-bond acceptor basicity (a), polarizability (s), and intercept (c) calculated using Eq. (5) from the retention data of 34 model compounds on 15 different stationary phases. Error bars indicate the confidence range at a 95% significance level (from [12]).

H hydrophobic interaction parameter 5 steric selectivity parameter A H-bond donor (acidity) parameter B H-bond acceptor (basicity) parameter C cation-exchange parameter (at dissociated silanols)... 

These equations make explicit the individual polar terms that are negatively related to lipophilicity and account for most polar interactions between a solute and the two solvent phases. In the case of the octanoi/water system (Eq. [6]), the main contributor to a solute s polarity is thus its H-bond acceptor basicity 0), and to a lesser extent its dipolarity/ polarizability (ir ). In contrast, the polar interactions expressed in alkane/ water partition coefficients (Eq. [7]) are the H-bond donor acidity (a) and the H-bond acceptor basicity 0), and again to a lesser extent the dipolarity/polarizability (ir ). 

H-Bond Donor (HBD) Inorganic acids Active H chlorides Active H fluorides Active H iodides Active H bromides ... 

We consider first the Sn2 type of process. (In some important Sn2 reactions the solvent may function as the nucleophile. We will treat solvent nucleophilicity as a separate topic in Chapter 8.) Basicity toward the proton, that is, the pKa of the conjugate acid of the nucleophile, has been found to be less successful as a model property for reactions at saturated carbon than for nucleophilic acyl transfers, although basicity must have some relationship to nucleophilicity. Bordwell et al. have demonstrated very satisfactory Brjinsted-type plots for nucleophilic displacements at saturated carbon when the basicities and reactivities are measured in polar aprotic solvents like dimethylsulfoxide. The problem of establishing such simple correlations in hydroxylic solvents lies in the varying solvation stabilization within a reaction series in H-bond donor solvents. 

H-bond donor/acceptors water, alcohols, carboxylic acids, amines, amides. 

The satisfactory correlations between Kamlet-Abraham s acidity parameters and H-bond donor free energy factors, and between Kamlet-Abraham s basicity parameters and H-bond acceptor free energy factors for many sets of compounds [26] deserve particular mentioning ... 

Fig. 20.2. Percentage of amino acids with H-bond donor side chains in the 12 putative transmembrane sequences of P-glycoprotein (P-gp). The transmembrane sequences were determined by means of a hydropathy plot according to Kyte and Doolitttle [100] and chosen to be 22 amino acids long. The first amino acid of each transmembrane sequence...

Fig. 1. Schematic illustrating three- and four-point 3D pharmacophores. Three-point 3D pharmacophores encode three functional group types and the three distances separating them, and four-point 3D pharmacophores encode four functional group types and the six distances separating them. Functional group types commonly included are acids, bases, hydrophobes, H-bond acceptors, H-bond donors, and aromatic systems. Distances are assigned to bins (e.g., 2.5-4.0 A) to limit the individual 3D pharmacophore descriptors to a tractable number, and to aid in comparing the individual 3D pharmacophores.

Br0nsted Acids, H-Bond Donors, and Combined Acid Systems in Asymmetric Catalysis... 

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