Proton-acceptor/donor capabilities

For the efficient electrooxidation of NAD(P)H, mediated electrocatalysis is necessary [22, 170, 171], and a wide range of diffusional mediators has been studied [188-193], Organic compounds that undergo two-electron reduction-oxidation processes and also function as proton acceptors-donors upon their redox transformations (such as ortho- and para-derivatives of quinones, phenylenedi-amines and aminophenols) have been found to be ideal for the mediation of NAD(P)H oxidation, although single-electron-transfer mediators (e.g. ferrocene derivatives) are also capable of oxidizing NAD(P)H [190, 191], Some compounds demonstrate very high rates for the mediated oxidation of NAD(P)H in aqueous solutions [188,189,194,195],... 

For example, nylon 66 will dissolve in formic acid, glacial acetic acid, phenol and cresol, four solvents which not only have similar solubility parameters but also are capable of acting as proton donors whilst the carbonyl groups on the nylon act as proton acceptors (Figure 5.6). 

Cations at the surface possess Lewis acidity, i.e. they behave as electron acceptors. The oxygen ions behave as proton acceptors and are thus Bronsted bases. This has consequences for adsorption, as we will see. According to Bronsted s concept of basicity, species capable of accepting a proton are called a base, while a Bronsted acid is a proton donor. In Lewis concept, every species that can accept an electron is an acid, while electron donors, such as molecules possessing electron lone pairs, are bases. Hence a Lewis base is in practice equivalent to a Bronsted base. However, the concepts of acidity are markedly different. 

Pentanone (2-Butanone) 102 2.82 Orientation with sone weak proton acceptor but not proton donor capabilities. 

The proton-acceptor capability of some 2-acetylselenophenes in dilute sulfuric acid has been determined by the 1H NMR method.97 With phenol as proton donor, hydrogen-bond formation can be studied using IR spectroscopy as the analytical method.98 Intramolecular hydrogen-bond formation... 

The mechanism of long-range proton transfer processes in solutions is complex becanse seqnential proton hops from initial proton donors to proton acceptors are mediated by water (or solvent) molecules or other groups capable of ionization. 

Un A hydrogen-bonding parameter which represents the lone-pair donor (proton acceptor) capability of the group. It is defined as the number of lone pairs on O and/or N atoms in the group. 

To fully characterize and categorize the solute selectivities of GC stationary phases, Rohrschneider and McRe5molds pioneered one of the earliest characterization methods [5,6]. The Rohrschneider-McReynolds system is the oldest and widely accepted stationary phase classification systems that is based on the retention of five probe molecules namely, benzene, bufanol, 2-penfanone, nifropropane, and pyridine. Each probe molecule is used to represenf a disfincf or a combination of interactions with the stationary phase. Benzene measures dispersive interactions with weak proton acceptor properties butanol measures dipolar interactions with both proton donor and proton acceptor capabilities 2-pentanone measures dipolar interactions with proton acceptor but not proton donor capabilities nitropropane measures weak dipolar interactions and pyridine measures weak dipolar interactions with strong proton acceptor but not proton donor capabilities. 

Organic solvents can also be classified according to their ability to accept or transfer protons (i.e., their acid-base behavior) [20,21]. Amphiprotic solvents possess donor as well as acceptor capabilities and can undergo autoprotolysis. They can be subdivided into neutral solvents that possess approximately equal donor and acceptor capabilities (water and alcohols), acidic solvents with predominantly proton donor properties (acetic acid, formic acid), and basic solvents with primarily proton acceptor characteristics (formamide, N-methylformamide, and N,N-dimethylformamide). Aprotic solvents are not capable of autoprotolysis but may be able to accept protons (ACN, DMSO, propylene carbonate). Inert solvents (hexane) neither accept nor donate protons nor are they capable of autoprotolysis. 

Proton acceptor. A functional group capable of accepting a proton from a proton donor molecule. 

The Bronsted theory of acids and bases defines an acid as a proton donor and a base as a proton acceptor, i.e. a pro tic acid such as hydrochloric acid is a source of protons. Although the idea of an acidic hydrogen in organic compounds may initially be understood in terms of a carboxyl hydroxyl group, a hydrogen atom may become weakly acidic in a number of other circumstances, e.g. when it is attached to a carbon atom that is adjacent to a carbonyl group. On the other hand, a base such as an amine, or a carboxylate anion, is capable of accepting a proton. 

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