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Protons exchange

Proton Exchange.—In some of the cases cited above, n.m.r. spectra have shown that protons exchange between bulk solvent and the co-ordination sphere both as such and as components of complete solvent molecules. The mechanism of proton transfer, as opposed to water exchange, from [Al(OH2)e] has been shown from n.m.r. kinetic studies and deuterium isotope experiments to be a bimolecular process. Proton transfer to [A1(0H)(0H2)6] + is significant. A A1 n.m.r. study of the same system at varying pH is consistent with bimolecular exchange. The variation of line-width with temperature is ascribed to changes in Al + + HjO Al(OH) + + H3O+ equilibrium rather than to kinetic effects. But A1 [Pg.141]

Dodd-Wing Fong and E. Grunwald, /. Amer. Chem. Soc., 1969, 91, 2413 A. Taka- [Pg.141]

Rates of proton exchange between bulk and co-ordinated water have also been determined for chromium(m), where, as for aluminium(iii), a bimolecular mechanism is indicated, and for berylliumfii).  [Pg.142]

Kinetic studies of substitution in tetrahedral complexes of metals in low oxidation states, for instance nickel tetracarbonyl or tetrakistrialkyl-phosphitenickel(o), are dealt with in the organometallic Chapter. Here we shall deal with reactions of oxoanions, isomerisation of tetrahedral complexes to square-planar forms and vice versa, and with the addition of ligands to tetrahedral to give octahedral complexes. [Pg.143]

Aquation of dichromate exhibits general-acid catalysis, which may operate by protonation of the bridging oxygen atom. The mechanism of aquation of the peroxoanion [0(02)4] has been investigated by kinetic and tracer experiments. The tracer results, and the observed effects of added inhibitors on reaction rates, show that the rate law for aquation is deceptively simple. Base hydrolysis of [Mo7024] to [Mo04] takes place by successive bimolecular attacks by hydroxide at the molybdenum atoms.  [Pg.143]


In molecular mechanics and molecular dynamics studies of proteins, assig-ment of standard, non-dynamical ionization states of protein titratable groups is a common practice. This assumption seems to be well justified because proton exchange times between protein and solution usually far exceed the time range of the MD simulations. We investigated to what extent the assumed protonation state of a protein influences its molecular dynamics trajectory, and how often our titration algorithm predicted ionization states identical to those imposed on the groups, when applied to a set of structures derived from a molecular dynamics trajectory [34]. As a model we took the bovine... [Pg.188]

Electrophilic Attack. A variety of boranes, heteroboranes, and metaHaboranes undergo electrophilic substitution. SusceptibiUty of boranes to electrophilic attack is often detected by deuteron—proton exchange experiments. Eor example, electrophilic hydrogen—deuterium exchange of occurs at the l-,2-,3-, and 4-positions when exposed to DCl in the presence of AlCl (81). The trend to increasing positive sites in is... [Pg.236]

Cyanuric acid is a titrable weak acid (pffai — 6.88, pifa2 — H-40, pffas — 13.5) (10). The pH of a saturated aqueous solution of pure CA at room temperature is - 4.8. Thermodynamic properties of CA are given ia Table 1. Spectroscopic data are available (1 3). Proton nmr is of limited usefulness because of proton exchange and CA s symmetry and low solubiUty. Nuclear quadmpole resonance measurements ( " N) have been reported (12). [Pg.417]

The two-proton exchange in pairs of OH O fragments of various carbonic acid dimers... [Pg.102]

Gluconolactone shows no exchange. The reason is that the tetrahedral intermediate is formed and breaks down stereoselectively. Even though proton exchange can occur in the tetrahedral intermediate, the anomeric effect leads to preferential loss of the axial oxygen. [Pg.161]

The enol can be observed by NMR spectroscopy and at —20°C has a half-life of several hours. At -1-20°C the half-life is only 10 minutes. The presence of bases causes very r id isomerization to acetaldehyde via the enolate. Solvents have a significant effect on the lifetime of such unstable enols. Solvents such as DMF and DMSO, which are known to slow rates of proton exchange by hydrogen bonding, increase the lifetime of unstable enols. ... [Pg.430]

The calculated energy differences give a good correlation with The p parameter (p = —17) is larger than that observed experimentally for proton exchange (p — 8). A physical interpretation of this is that the theoretical results pertain to the gas phase, where... [Pg.559]

Comparison of localization energies has frequently been applied to prediction of the relative positional reactivity in polycyclic aromatic hydrocarbons. Simple HMO calculations have only marginal success. CNDO/2 and SCF calculations give results which show good correlation with experimental data on the rate of proton exchange. ... [Pg.560]

Consider a nucleus that can partition between two magnetically nonequivalent sites. Examples would be protons or carbon atoms involved in cis-trans isomerization, rotation about the carbon—nitrogen atom in amides, proton exchange between solute and solvent or between two conjugate acid-base pairs, or molecular complex formation. In the NMR context the nucleus is said to undergo chemical exchange between the sites. Chemical exchange is a relaxation mechanism, because it is a means by which the nucleus in one site (state) is enabled to leave that state. [Pg.166]

Much information on proton transfers has been obtained by NMR chemical exchange studies. An example is the proton exchange between neopentyl alcohol and acetic acid in acetic acid as the solvent. The reaction is... [Pg.173]

Another example is the proton exchange between H2O and HDO at low water concentrations in organic solvents. t values were obtained by line shape analysis ... [Pg.173]

Attempts were undertaken to evaluate the rates of proton exchanges 24a 24b 24c and 25a 25b 25c in solutions of 1,2,3-triazole and... [Pg.186]


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Acid-catalyzed reactions proton exchange

Acidic and Exchangeable Protons Hydrogen Bonding

Acidic protons, exchange

Activation energy for proton exchange

Adsorption proton exchange

Alkylidene proton exchange

Amide protons, exchange reaction

Amine proton exchange

Aromatic protons, exchange

Base hydrolysis proton exchange

Benzophenones, proton exchange

Catalyst Support Materials for Proton Exchange Membrane Fuel Cells

Chemical degradation proton exchange membrane

Chemical exchange acidic protons

Composite electrolytes for proton exchange membrane fuel cells

Composite polymer electrolytes proton exchange membrane fuel

Cyanide exchange protonated complexes

Deuterium, exchange with proton

Deuteron-proton exchange

Direct Methanol Proton Exchange Fuel Cell

Direct methanol fuel cell proton-exchange membrane

Durability of Fluoropolymers for Proton Exchange Membranes

Electrocatalyst Design in Proton Exchange Membrane Fuel Cells for Automotive Application

Electrodes proton exchange membrane

Electrolytes proton-exchange membrane

Electrolyzer proton exchange membrane

Electrolyzers Proton Exchange

Electrolyzers Proton Exchange Membrane

Electrophilic aromatic substitution proton exchange

Enzyme reactions proton exchange rates

Exchange rates, amide protons

Exchange reactions between amino protons

Exchange reactions between hydroxyl protons

Exchange reactions, proton magnetic

Exchange, of acidic protons

Exchange, proton/deuterium

Exchangeability of OH proton

Exchangeable and Nonexchangeable Protons

Exchangeable proton signals

Exchangeable proton signals temperature dependence

Exchangeable protons

Exchangeable protons, assignments

Fabrication of electro-catalytic nano-particles and applications to proton exchange membrane fuel cells

Fast proton exchange

Fuel cell proton exchange

Fuel cell, proton-exchange membrane fundamental research

Fuel cells proton exchange membrane

Fuel cells, proton-exchanging

Fuel cells, proton-exchanging membranes

Fuel proton-exchange membrane (PEMFC

Halogen-metal exchange reaction, acidic proton

High-temperature proton exchange

High-temperature proton exchange PEEK membrane

High-temperature proton exchange acid-base polymer membrane

High-temperature proton exchange benefits

High-temperature proton exchange electrode kinetics

High-temperature proton exchange membrane

High-temperature proton exchange membrane examples

High-temperature proton exchange membrane fuel cell

High-temperature proton exchange methanol reformer

Hydrocarbon polymers proton exchange membranes based

Hydrocarbon proton exchange membrane

Hydrogen Bonding, Tautomerism and Proton Exchange

Hydrogen proton exchange

Hydrogen proton exchange Electrode Assemblies

Hydrogen proton exchange Specialized Membrane

Hydrogen proton exchange barriers

Hydrogen proton exchange membrane fuel cell

Hydrogen proton exchange membranes

Hydrogen proton exchange transportation

Hyperfine-shifted proton resonances exchangeable, deoxy

Imidazole 1-oxides proton exchange

Intermolecular proton exchange, rate

Intramolecular proton exchange

Inversion and Proton Exchange at Asymmetric Nitrogen

Ion-proton exchange

Line broadening exchangeable protons

Low-humidity proton exchange membrane fuel

Membranes proton-exchanging

Metal-proton exchange reaction

Metalloproteins proton exchange

Models proton exchange

Molecular proton-exchanged

Molybdenum complexes proton exchange

NMR spectroscopy exchangable protons

Na+-Proton Exchanger

Naphthalene proton exchange

New Proton Exchange Membranes

Nuclear magnetic resonance proton exchange

Perfluorinated proton exchange

Precipitants Protons, exchangeable

Proteins proton exchange rates

Proteins tryptophan proton exchange

Proton Cleavage, heterolytic Exchange processes

Proton Exchange Kinetics

Proton Exchange Membrane Fuel Cells 5 Alternative Supports

Proton abstraction exchange

Proton exchange amine ligands

Proton exchange by electrophilic aromatic substitution

Proton exchange by enolization, measurement

Proton exchange catalysis

Proton exchange electrolyte fuel cell

Proton exchange equilibria

Proton exchange in measurement of hydrocarbon acidity

Proton exchange membran

Proton exchange membrane

Proton exchange membrane -based

Proton exchange membrane -based direct methanol fuel cell

Proton exchange membrane DEFC

Proton exchange membrane advantage

Proton exchange membrane bipolar plates

Proton exchange membrane blend

Proton exchange membrane block copolymer

Proton exchange membrane cells

Proton exchange membrane chemical stability

Proton exchange membrane composite

Proton exchange membrane conductors

Proton exchange membrane density

Proton exchange membrane design

Proton exchange membrane direct hydrogen

Proton exchange membrane electrocatalysts

Proton exchange membrane electrolyser

Proton exchange membrane electrolysis

Proton exchange membrane electrolysis cell

Proton exchange membrane fluorinated block copolymer

Proton exchange membrane fluorinated sulfonated

Proton exchange membrane fluoropolymers

Proton exchange membrane fuel

Proton exchange membrane fuel cell PEMFC) technology

Proton exchange membrane fuel cell accelerated testing

Proton exchange membrane fuel cell ammonia

Proton exchange membrane fuel cell anode contamination

Proton exchange membrane fuel cell catalyst layers

Proton exchange membrane fuel cell components

Proton exchange membrane fuel cell compounds

Proton exchange membrane fuel cell contamination

Proton exchange membrane fuel cell cost efficiency

Proton exchange membrane fuel cell current generation

Proton exchange membrane fuel cell disadvantages

Proton exchange membrane fuel cell durability

Proton exchange membrane fuel cell electrical energy efficiency

Proton exchange membrane fuel cell electrolysis

Proton exchange membrane fuel cell fabrication process

Proton exchange membrane fuel cell hydrogen crossover

Proton exchange membrane fuel cell hydrogen economy

Proton exchange membrane fuel cell impact

Proton exchange membrane fuel cell impurities

Proton exchange membrane fuel cell polarization curve

Proton exchange membrane fuel cell power density

Proton exchange membrane fuel cell reformate feed

Proton exchange membrane fuel cell relative humidity

Proton exchange membrane fuel cell solid electrolyte

Proton exchange membrane fuel cell structure

Proton exchange membrane fuel cell technique

Proton exchange membrane fuel cell transportation

Proton exchange membrane fuel cell transportation applications

Proton exchange membrane fuel cells PEMFC)

Proton exchange membrane fuel cells PEMFCs)

Proton exchange membrane fuel cells Purification

Proton exchange membrane fuel cells advantages

Proton exchange membrane fuel cells anode catalyst materials

Proton exchange membrane fuel cells application fields

Proton exchange membrane fuel cells bipolar plate materials

Proton exchange membrane fuel cells carbon monoxide-tolerant

Proton exchange membrane fuel cells cathode catalyst

Proton exchange membrane fuel cells companies developing

Proton exchange membrane fuel cells comparison

Proton exchange membrane fuel cells electrocatalysts

Proton exchange membrane fuel cells electrochemical properties

Proton exchange membrane fuel cells electrochemical reactions

Proton exchange membrane fuel cells electrodes

Proton exchange membrane fuel cells electron conductivity

Proton exchange membrane fuel cells functions

Proton exchange membrane fuel cells hydrocarbon

Proton exchange membrane fuel cells materials

Proton exchange membrane fuel cells membranes

Proton exchange membrane fuel cells methods

Proton exchange membrane fuel cells optimization

Proton exchange membrane fuel cells perfluorosulfonic acid

Proton exchange membrane fuel cells permeability

Proton exchange membrane fuel cells platinum catalysts

Proton exchange membrane fuel cells polybenzimidazole

Proton exchange membrane fuel cells reliability

Proton exchange membrane fuel cells schematic

Proton exchange membrane fuel cells schematic diagram

Proton exchange membrane fuel cells support materials

Proton exchange membrane fuel cells technology

Proton exchange membrane fuel cells vulcan

Proton exchange membrane fuel cells water management

Proton exchange membrane fuel cells, PEM

Proton exchange membrane future directions

Proton exchange membrane graft copolymer

Proton exchange membrane impedance measurements

Proton exchange membrane intermediates

Proton exchange membrane ionomer

Proton exchange membrane manufacturing

Proton exchange membrane materials

Proton exchange membrane mechanical properties

Proton exchange membrane methanol crossover

Proton exchange membrane nanocomposite

Proton exchange membrane oxygen permeability

Proton exchange membrane perfluorinated

Proton exchange membrane performance comparison

Proton exchange membrane phenomenology

Proton exchange membrane polymer blends

Proton exchange membrane radiation-grafted

Proton exchange membrane relationships

Proton exchange membrane sPEEK

Proton exchange membrane stability

Proton exchange membrane statistical copolymers

Proton exchange membrane water flooding

Proton exchange membrane water transport

Proton exchange membranes development

Proton exchange membranes for fuel cells

Proton exchange membranes properties

Proton exchange polymer membranes

Proton exchange rate

Proton exchange rates effect

Proton exchange reaction

Proton exchange reactions system

Proton exchange stereochemistry

Proton exchange tautomerism

Proton exchange transition metal complexes

Proton exchange, Chap

Proton exchange, Raman spectroscopy

Proton exchange, acid- base

Proton exchange, between silanols

Proton exchange, racemization

Proton magnetic resonance spectroscopy chemical exchange

Proton-Exchange Membrane Fuel Cells Pyoungho Choi, Pradeep Haidar, and Ravindra Datta

Proton-Metal Exchange with Acidic Hydrocarbons

Proton-exchange membrane fuel cell applications

Proton-exchange membrane fuel cell electrocatalysis

Proton-exchange membrane fuel cell performance

Proton-exchange membrane fuel cell temperature

Proton-exchange membrane fuel cells bipolar plates

Proton-exchange membrane fuel cells efficiency

Proton-exchange membrane fuel cells hydrogen storage

Proton-exchange membrane fuel cells kinetics

Proton-exchange membrane fuel cells principles

Proton-exchange membrane fuel cells reaction mechanisms

Proton-exchange membrane fuel cells thermodynamics

Proton-exchange membrane fuel cells types

Proton-exchange processes

Protonation and Hydrogen Exchange

Pyridines proton exchange

Rate of proton exchange

Redox Titrations in Which a Simultaneous Exchange of Electrons and Protons or Other Particules Exists

Rhenium complexes proton exchange

Ring proton exchange

Sodium-proton exchanger

Sulfhydryl group proton exchange

Technetium complexes proton exchange

Thallium proton exchange

The Effect of Proton (Cation) Exchange Level

The Proton Exchange Membrane

The Proton Exchange Membrane Fuel Cell (PEMFC)

Tryptophan proton exchange

Tungsten complexes proton exchange

Water/proton exchange rate

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