Effect of Hydrogen Bonds on pK_a Values: Importance of Networking

Abstract

The pK(a) of an acyclic aliphatic heptaol ((HOCH(2)CH(2)CH(OH)CH(2))(3)COH) was measured in DMSO, and its gas-phase acidity is reported as well. This tertiary alcohol was found to be 10(21) times more acidic than tert-butyl alcohol in DMSO and an order of magnitude more acidic than acetic acid (i.e., pK(a) = 11.4 vs 12.3). This can be attributed to a 21.9 kcal mol(-1) stabilization of the charged oxygen center in the conjugate base by three hydrogen bonds and another 6.3 kcal mol(-1) stabilization resulting from an additional three hydrogen bonds between the uncharged primary and secondary hydroxyl groups. Charge delocalization by both the first and second solvation shells may be used to facilitate enzymatic reactions. Acidity constants of a series of polyols were also computed, and the combination of hydrogen-bonding and electron-withdrawing substituents was found to afford acids that are predicted to be extremely acidic in DMSO (i.e., pK(a) < 0). These hydrogen bond enhanced acids represent an attractive class of Brønsted acid catalysts.

Aromatic and Hydrophobic Surfaces of Wood-derived Biochar Enhance Perchlorate Adsorption via Hydrogen Bonding to Oxygen-containing Organic Groups

“…For each sample (FB200-FB700), there were some differences among their individual inflection points (named pH d1 and pH d2 , marked in Figure 2). For instance, pH d1 and pH d2 for FB300-FB400 were located at pH values of 5 and 9, respectively, while the pH d1 and pH d2 for the high temperature samples appeared at pH values of 6 and 10, respectively; this effect can be ascribed to the effects of substrate structure on the dissociation of functional groups, 47,48 and the obtained structural characteristics showed significant differences in functional group dissociation for biochars produced at different temperatures. Coupled with FTIR spectra of −OH and −COOH bands on biochars, the pH d1 and pH d2 correspond to the dissociation of carboxyl and hydroxyl groups, respectively.…”

Cooperativity effects of intramolecular OH…O interactions on pK a values of polyolalkyl sulfonic acids in the gas phase and solution: a density functional theory study

“…As a result, optimization of all structures was performed in H 2 O (water), DMSO (dimethyl sulfoxide), and CH 3 CN (acetonitrile) using PCM model and B3LYP/6‐311++G(d,p) level of theory. Prediction of p K a values in H 2 O, DMSO, and CH 3 CN was performed using Eqn , where [∆ (kcal/mol)]/1.364 = p K a (HX) − p K a (CH 3 SO 3 H) or p K a (HX) = p K a (CH 3 SO 3 H) + [∆ (kcal/mol)]/1.364 …”

“…Therefore, determining p K a values computationally has become a subject of extensive interest. For instance, we have recently studied the effect of hydrogen bond on p K a values of heptol and a series of polyols in DMSO …”

Does Hydrogen‐Bonding Donation to Manganese(IV)–Oxo and Iron(IV)–Oxo Oxidants Affect the Oxygen‐Atom Transfer Ability? A Computational Study

“…[11] In particular, addition of Zn 2 + to a manganese(V)-oxo corrolazine system changed the electronic state to a manganese(IV)oxo corrolazine cation radical and improved its catalytic properties through valence tautomerism. [17] Recent studies of Kass an co-workers [18] showed that intramolecular hydrogen bonding can dramatically influence the pK a values of molecules and thereby play a key role in reactivities. [13] In one of these studies, Borovik and co-workers focused on metal-oxo complexes, [M IV (O)A C H T U N G T R E N N U N G (H 3 buea)] À (M = Fe, Mn; H 3 buea = tris[N'-tert-butylureayl-N-ethylene]amine; Scheme 1).…”