Acidities and hydrogen bonding of phenols in dimethyl sulfoxide
About: This article is published in Journal of Organic Chemistry.The article was published on 1984-04-01. It has received 157 citations till now. The article focuses on the topics: Cresol & Hydrogen bond.
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TL;DR: The first acidity scale to be established in a pure solvent other than water was the result of the pioneering work of Conant, Wheland, and McEwen in ether or ben~ene.
Abstract: The first acidity scale to be established in a pure solvent other than water was the result of the pioneering work of Conant, Wheland, and McEwen in ether or ben~ene .~ During the past 20 years an ion-pair acidity scale covering an \"effective pKa rangefrom about 15 to 40 has been developed in cyclohexylamine (CHA),6 and similar studies in other low-dielectric-constant solvents including 1,2-dimethoxyethane (DME)7a and tetrahydrofuran (THF)7b*c have been carried out. A more limited ion-pair acidity scale has been developed in liquid NH,.7d Also, during this period, acidity scales have been established in the polar non-hydrogenbond-donor (NHBD) solvents dimethyl sulfoxide (Me$0)8 and N-methylpyrrolidin-2-one (NMP)? which have relatively high dielectric constants. The pK,'s measured in these solvents differ from ion-pair pK,'s in that they are absolute, in the sense that they are based on Me2S0 and NMP as the standard states, which allows direct comparisons to be made with H20 and gas-phase pK,'s. A truly absolute acidity scale has been established in the gas phase, which, for the first time, provides intrinsic measures of structural effects free of solvent effects.1° Our purpose in this Account is (a) to discuss briefly acidities in various solvent media, (b) to present a table of representative equilibrium acidity constants in M e 8 0 solution, and (c) to illustrate ways in which these pK, data can be used. In an accompanying Account we compare acidities in Me2S0 solution with intrinsic gas-phase acidities and discuss some of the insights into solvation effects provided thereby. Acidities in H 2 0 and Me2S0. It is important to recognize that pKa values are solvent dependent. The
2,383 citations
TL;DR: Binaphthol-derived monophosphoric acids have been designed as novel chiral Brønsted-acid catalysts, which function as efficient enantioselective catalysts for a variety of organic transformations, especially for carbon-carbon bond forming reactions.
838 citations
TL;DR: This proposal that short, strong hydrogen bonds exist in enzyme active sites and that they are important in explaining enzymic rate enhancements is defended and evidence for likely changes of hydrogen bond strengths during enzyme catalysis is provided.
305 citations
TL;DR: The bioisosterism of the OH and CF2H groups and the important roles of CF2-H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences are demonstrated.
Abstract: The CF2H group, a potential surrogate for the OH group, can act as an unusual hydrogen bond donor, as confirmed by crystallographic, spectroscopic, and computational methods. Here, we demonstrate the bioisosterism of the OH and CF2H groups and the important roles of CF2–H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences. Experimental evidence, corroborated by theory, reveals the distinctive nature of CF2H hydrogen bonding interactions relative to their normal OH hydrogen bonding counterparts.
270 citations
TL;DR: These results and those of other model studies suggest alternative mechanisms by which hydrogen bonds can contribute to enzymatic catalysis, in accord with conventional electrostatic considerations.
Abstract: Low-barrier or short, strong hydrogen bonds have been proposed to contribute 10 to 20 kilocalories per mole to transition-state stabilization in enzymatic catalysis The proposal invokes a large increase in hydrogen bond energy when the pKa values of the donor and acceptor (where Ka is the acid constant) become matched in the transition state (delta pKa=0) This hypothesis was tested by investigating the energetics of hydrogen bonds as a function of delta pKa for homologous series of compounds under nonaqueous conditions that are conducive to the formation of low-barrier hydrogen bonds In all cases, there was a linear correlation between the increase in hydrogen-bond energy and the decrease in delta pKa, as expected from simple electrostatic effects However, no additional energetic contribution to the hydrogen bond was observed at delta pKa=0 These results and those of other model studies suggest alternative mechanisms by which hydrogen bonds can contribute to enzymatic catalysis, in accord with conventional electrostatic considerations
244 citations