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Proton - transfer reaction

Reactions of this type are important in some gases and certainly in many gaseous mixtures. The basic proton donors are H3+, CH5+, and ions of the types C H+2n + L and C H,, + in addition to certain others. In some cases, such as in cyclo-propane, the product of the proton transfer reaction is a stable ion  [Pg.124]

In many other cases, the resultant ion decomposes (dissociative proton transfer). Examples are [Pg.124]

Similarly, when CH4 containing a little n-C5D12 is irradiated the immediate product of the proton-transfer reaction, C5D12H+ will dissociate in several different ways. It is believed that (1) the relative probability of dissociative proton transfer reaction increases with exothermicity (2) at high pressures, the different modes of dissociation on proton transfer from H3+ are about equally competitive and (3) there is little or no H atom reshuffling on proton transfer (Ausloos and Lias, 1967). The last-mentioned item may be established by isotope studies. [Pg.125]

Proton Transfer in the Case of Strong Coupiihg with the Medium [Pg.20]

Considering proton transfer reactions in polar liquids (e.g., water), it may be expected that the interaction of the reactants with the medium will be strong, i.e., the solvent reorganization energy in the reaction will be large E r i.e., [Pg.20]

First we shall consider entirely nonadiabatic reactions for which formulas of the quantum mechanical perturbation theory in the first order in the interaction, leading to reaction may be used for the calculation of the [Pg.20]

formally, the change of the proton state is reduced to the change of the electron resonance integral, Vjf by V f S, All the temperature dependence of the transition probability for a fixed value of the coordinate of the reactant center of mass is related to the classical overcoming of the Franck-Condon barrier created by the solvent polarization. [Pg.21]

Equation (38) is convenient if the harmonic approximation is sufficient. However, if the intramolecular vibrations are essentially anharmonic, the formula (46) is more convenient  [Pg.23]

4 Through-Shell Reactions 9.4.1 Proton Transfer Reactions [Pg.233]

The rate constants for gas-phase proton transfer reactions of N2H are summarized in Table 6. The rate constants generally refer to thermal or near-thermal measurements at room temperature. Further information on the tabulated reactions and on other proton transfer reactions is given in the text. For some comments regarding experimental techniques used in studying gas-phase ion molecule reactions, see p. 6. [Pg.31]

Predictions of collision rate constants for systems in which a reactive collision of N2H with its partner would result in proton transfer have not been treated in the text. Such collision rate constants obtained using classical theories, such as the Langevin ion-induced dipole theory, the locked-dipole theory, and the average dipole orientation theory, are given, for example, in [1 to 11]. Langevin rate constants for the reactions of N2H with many species, including those for which there are no laboratory data (for example C, S, NH, OH, CH2, NH2, HCO, C2H), are given in [12]. [Pg.31]

The analysis of the N2H decay yielded the second rate constants k = 2.2xio (CO2) [Pg.32]

Proton transfer to Ar was observed in a flow-drift tube study [32]. The dependence of the absolute cross sections for the N2D + Ar- ArD +N2 reaction in the forward and reverse directions on the center-of-mass kinetic energy of the colliding particles (0 to 15 eV) was studied using a twin mass spectrometer apparatus [33]. [Pg.32]

The proton transfer reaction N2H + Xe XeH + N2 in the forward and back directions was investigated between 300 to 800 K. The equilibrium constant K = 58 8 at 297 [Pg.32]

However, quantal and molecular treatments of proton transfer reactions at an electrode are rare. This treatment incorporates the major effect of an electric field as well as some of the important concepts reported earlier by Bockris and Matthews concerning proton transfer reactions at an electrode. [Pg.104]

In this treatment, the potential energies of the initial state, where the transferring proton is in the solution as a hydronium ion (H30 )and in the final state as an adsorbed hydrogen atom on the metal surface, were given [Pg.104]

M is its effective mass, R is its reaction coordinate, and r,-, are its equilibrium positions in the initial and final states. [Pg.105]

This model has obvious shortcomings. For example, the interaction with the solvent in the initial state is straightforward since the proton is in the ionic form, whereas in the final state, the proton is the nonionic adsorbed H atom and its interaction with the solvent should be negligible. No consideration of this fact was made in the potential of the final state Uf m Eq. (43). However, this treatment incorporates the basic feature of the proton transfer reaction interaction with the solvent, tunneling as well as classical transition of the proton, and the effect of the electric field on the potential energy surfaces of the system. [Pg.105]

The cathodic current density for the neutralization of the proton at an electrode was obtained using first-order perturbation theory and was expressed in nonquadratic form as [Pg.105]

In the reaction that occurs when HCl dissolves in water, the HCl molecule transfers an H ion (a proton) to a water molecule. Thus, we can represent the reaction as occurring between an HCl molecule and a water molecule to form hydronium and chloride ions  [Pg.673]

Notice that the reaction in Equation 16.3 involves a proton donor (HCl) and proton acceptor (H2O). The notion of transfer from a proton donor to a proton acceptor is the key idea in the Bronsted-Lowry definition of acids and bases  [Pg.673]

when HCl dissolves in water (Equation 16.3), HCl acts as a Bronsted-Lowry acid (it donates a proton to H2O), and H2O acts as a Bronsted-Lowry base (it accepts a proton from HCl). We see that the H2O molecule serves as a proton acceptor by using one of the nonbonding pedrs of electrons on the O atom to attach the proton. [Pg.674]

Because the emphasis in the Bronsted-Lowry concept is on proton transfer, the concept also applies to reactions that do not occur in aqueous solution. In the reaction between gas phase HCl and NH3, for example, a proton is trcuisferred from the acid HCl to the base NH3  [Pg.674]

Let s consider another example that compares the relationship between the Arrhenius and Bronsted-Lowry definitions of acids and bases—an aqueous solution of ammonia, in which we have the equilibrium  [Pg.674]

A FIGURE 16.2 Ball-and-stick models and Lewis structures for two hydrated hydronium ions. [Pg.653]

The polar H2O molecule promotes the ionization of acids in water solution by accepting a proton to form H3O.  [Pg.653]

Br0nsted and Lowry proposed definitions of acids and bases in terms of their ability to transfer protons  [Pg.653]

Not only the nitroaromatic species, such as IV, but also some simpler compounds, which used to be considered as typical substrates of the 8 2 reactions, can be involved in multistep radical-forming nucleophilic substitutions. Evidence has been accumulating over the last years that the nucleophilic substitution with alkyl halides occurs, at least in some instances, by the single-electron transfer mechanism. It has been suggested [29,30] that the SET and Sn2 mechanisms represent the extremes of a wide spectrum of mechanistic possibilities for substitution reactions. It has been deduced on qualitative theoretical grounds that the propensity of alkyl halide R—X to react with nucleophiles via an electron-transfer step depends crucially on the stability of the three-electron bond R—X in the initially formed radical-anion species. A more electronegative R will stabilize this bond and bring about a shift in the mechanism from the Sn2 to the SET type, which has then experimentally been shown to be a correct conclusion, see Ref. [30]. [Pg.217]

This brief theoretical analysis of the mechanism of the SrnI reaction of Eq. (9.3) shows how complicated the complete calculation may be of the reaction pathways associated with the electron transfer in polar solvents. But it also shows how one should, within the framework of realistic possibilities, approach the problems that have to do with the examination and identification of organic reactions of this type. [Pg.217]

So as to ascertain a possibility of the electron transfer in a certain reaction phase, a quite useful criterion may be obtained through an analysis of the Hartree-Fock triplet (doublet in the case of radicals) stabilities of solutions (see Sect. 2.2.5). Since such an analysis is relatively simple, it should precede a more rigorous examination similar to that described in this section. Some examples of how an analysis of stability of the HF-solutions may be used in calculations on the reactions with a possible electron transfer are considered in Sect. 5.4, 6.1, and 8.3. [Pg.217]

First assumptions as to the possibility of hydrogen changing its position in the process of transformation of one chemical particle into another one were voiced nearly 200 years ago [31], and the mechanism of this enormously important reaction has been attracting attention ever since. The reason for this interest is obvious seeing that the proton transfer reactions underlie the acid-base equilibria and determine the mechanisms of a broad range of biological phenomena such as the transport across membranes, enzymic catalysis, photosynthesis, the formation of the ATP acid, spontaneous mutations etc. [Pg.217]

Similarly to the electron transfer reactions, a proton transfer is preceded by the formation of an intermediate associate which in this case is a hydrogen bond complex (H-complex) V  [Pg.217]

6 n 15 it increases smoothly, until for 16 it has reached unity. The onset of complete caging for n 16 is due to the formation of the first so-called solvation shell. [Pg.353]

Proton-transfer reactions play a key role in solution chemistry, and more specifically in acid-base reactions. Conceptually, the bond-breaking and bondmaking dynamics in any chemical reaction involve the redistribution of electrons between old and new bonds. In the class of reactions denoted as proton-transfer reactions, the crucial step involves the motion of a hydrogen atom (H), which typically occurs on the picosecond or femtosecond time-scale. [Pg.353]

CH25 SOLVAnON DYNAMICS ELEMENTARY REACnONS IN SOLVENT CAGES [Pg.354]

Proton-transfer reactions have been studied in finite-size clusters involving ammonia or water as solvent molecules. One particular system falling into this category has been studied extensively, namely 1-naphthol, here referred to as AH, solvated by ammonia. [Pg.354]

Generally speaking, the specific proton-transfer reaction for AH can be written as [Pg.354]


Figure A3.8.3 Quantum activation free energy curves calculated for the model A-H-A proton transfer reaction described 45. The frill line is for the classical limit of the proton transfer solute in isolation, while the other curves are for different fully quantized cases. The rigid curves were calculated by keeping the A-A distance fixed. An important feature here is the direct effect of the solvent activation process on both the solvated rigid and flexible solute curves. Another feature is the effect of a fluctuating A-A distance which both lowers the activation free energy and reduces the influence of the solvent. The latter feature enliances the rate by a factor of 20 over the rigid case. Figure A3.8.3 Quantum activation free energy curves calculated for the model A-H-A proton transfer reaction described 45. The frill line is for the classical limit of the proton transfer solute in isolation, while the other curves are for different fully quantized cases. The rigid curves were calculated by keeping the A-A distance fixed. An important feature here is the direct effect of the solvent activation process on both the solvated rigid and flexible solute curves. Another feature is the effect of a fluctuating A-A distance which both lowers the activation free energy and reduces the influence of the solvent. The latter feature enliances the rate by a factor of 20 over the rigid case.
Lobaugh J and Voth G A 1994 A path integral study of electronic polarization and nonlinear coupling effects in condensed phase proton transfer reactions J. Chem. Phys. 100 3039... [Pg.898]

The phenomenon of intemiolecular exchange is very common. The loss of couplings to hydroxyl protons in all but the very purest etiianol samples was observed at a very early stage. Proton transfer reactions are still probably the most carellilly studied [14] class of intemiolecular exchange. [Pg.2103]

Drukker, K., Hammes-Schiffer, S. An analytical derivation of MC-SCF vibrational wave functions for the quantum dynamical simulation of multiple proton transfer reactions Initial application to protonated water chains. J. Chem. Phys. 107 (1997) 363-374. [Pg.33]

Hammes-Schiffer Multiconflgurational molecular dynamics with quantum transitions Multiple proton transfer reactions. J. Chem. Phys. 105 (1996) 2236-2246. [Pg.34]

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... [Pg.637]

Steps 2 and 4 are proton transfer reactions and are very fast Nucleophilic addi tion to the carbonyl group has a higher activation energy than dissociation of the tetra hedral intermediate step 1 is rate determining... [Pg.855]

Table 8.7 Proton Transfer Reactions of Inorganic Materials in Water at 25°C 8.18... Table 8.7 Proton Transfer Reactions of Inorganic Materials in Water at 25°C 8.18...
Table 8.11 pK, Values for Proton-Transfer Reactions in Nonaqueous Solvents 8.81... [Pg.828]

The values listed in Tables 8.7 and 8.8 are the negative (decadic) logarithms of the acidic dissociation constant, i.e., — logj, For the general proton-transfer reaction... [Pg.844]

In Section 8, the material on solubility constants has been doubled to 550 entries. Sections on proton transfer reactions, including some at various temperatures, formation constants of metal complexes with organic and inorganic ligands, buffer solutions of all types, reference electrodes, indicators, and electrode potentials are retained with some revisions. The material on conductances has been revised and expanded, particularly in the table on limiting equivalent ionic conductances. [Pg.1284]

R. J. Gillespie, in V. Gold, ed.. Proton Transfer Reactions, Chapman and Hall, London, 1975, p. 27. [Pg.151]

A Warshel. Dynamics of reactions m polar solvents. Semiclassical trajectory studies of electron-transfer and proton-transfer reactions. J Phys Chem 86 2218-2224, 1982. [Pg.415]

Because proton-transfer reactions between oxygen atoms are usually very fast, step 3 can be assumed to be a rapid equilibrium. With the above mechanism assume4 let us examine the rate expression which would result, depending upon which of the steps is rate-determining. [Pg.198]

It is possible to measure equilibrium constants and heats of reaction in the gas phase by using mass spectrometers of special configuration. With proton-transfer reactions, for example, the equilibrium constant can be determined by measuring the ratio of two reactant species competing for protons. Table 4.13 compares of phenol ionizations. [Pg.244]

In analyzing the behavior of these types of tetrahedral intermediates, it should be kept in mind that proton-transfer reactions are usually fast relative to other steps. This circumstance permits the possibility that a minor species in equilibrium with the major species may be the major intermediate. Detailed studies of kinetics, solvent isotope effects, and the nature of catalysis are the best tools for investigating the various possibilities. [Pg.481]

Table 10.1. Energy Changes for Isodesmic Proton-Transfer Reactions of Substituted Benzenes"... Table 10.1. Energy Changes for Isodesmic Proton-Transfer Reactions of Substituted Benzenes"...
Most proton transfer reactions are fast they have been carefully studied by relaxation methods. A system consisting of a conjugate acid-base pair in water is a three-state cyclic equilibrium as shown in Scheme IV. [The symbolism is that used by Bemasconi. ... [Pg.146]

Table 4-1. Rate Constants for Proton Transfer Reactions in Water ... Table 4-1. Rate Constants for Proton Transfer Reactions in Water ...
We will now consider in qualitative terms the important class of proton-transfer reactions... [Pg.296]


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3-Hydroxyflavone. proton-transfer reactions

A Proton Transfer Reaction from Acids to Bases

Acid-Base Catalysis and Proton-Transfer Reactions

Acid-Base Reactions A Mechanism for Proton Transfer

Acid-base equilibria proton-transfer reactions

Acid-base reactions proton transfer

Acid-dissociation constant proton-transfer reactions

Acids, acid proton-transfer reaction

Activation energy proton transfer reactions

Alkylation proton transfer reaction

All-Atom Models for Proton Transfer Reactions in Enzymes

Aspirin proton transfer reaction

Bimolecular Proton Transfer Reactions

Carbanions proton-transfer reactions

Chemical reaction proton transfer

Classical proton transfer reaction

Clusters proton transfer reactions

Concerted proton-transfer reactions

Covalent proton transfer reaction

Dihydrogen Bonds as Intermediates in Intermolecular Proton Transfer Reactions

Direct intramolecular proton transfer reaction

Dynamics Simulations of Proton Transfer Reactions in Solution

Dynamics of Ground- and Excited-State Intramolecular Proton Transfer Reactions

Electron and Proton Transfer Reactions

Energy proton transfer reactions

Excited state proton transfer reactions

Experimental Approaches Towards Proton-Coupled Electron Transfer Reactions in Biological Redox Systems

General Proton-Transfer Reactions

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Ground-state intramolecular proton transfer reactions

Hydrogen catalytic proton transfer reactions

Intermolecular reactions Proton transfer

Intramolecular reactions Proton transfer

Isomerases 1,2-proton transfer reactions

Kemp elimination reactions proton transfers

Kinetic isotope effects in proton-transfer reactions

Kinetic isotope effects, benzophenoneA/iV-dimethylaniline proton-transfer reactions

Landau-Zener crossing formalism proton-transfer reactions

Mass proton transfer reaction

Mechanism for proton-transfer reactions

Membrane inlet proton transfer reaction mass spectrometry

Metal proton transfer reactions

Metal-peptides proton transfer reactions

Molecular proton transfer reactions with

Nitroalkanes, proton-transfer reactions

Nitromethane proton transfer reactions

Organic compounds proton-transfer reactions

Other Diffraction Methods Used to Study Proton Transfer Reactions

Partial proton transfer reactions

Peptide-metal complexes proton-transfer reactions

Peptides proton transfer reactions

Polar solvents, proton transfer reactions

Polar solvents, proton transfer reactions theory

Polarity proton transfer reactions

Potential surfaces for proton transfer reactions

Proton Transfer A Closer Look at Acid-Base Reactions

Proton Transfer Reactions and the EVB Model

Proton Transfer Reactions of Simple and Aryl Nitroalkanes in Solution

Proton Transfer to and from Carbon in Model Reactions

Proton affinity transfer reaction

Proton and Hydride Transfer Reactions

Proton reactions

Proton transfer in acid-base reactions

Proton transfer reaction mass spectrometer

Proton transfer reaction mass spectrometry

Proton transfer reaction mass spectrometry PTR-MS)

Proton transfer reaction mass spectrometry applications

Proton transfer reaction mass spectrometry drift tube

Proton transfer reaction mass spectrometry environmental

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Proton transfer reaction mass spectrometry medical

Proton transfer reaction mass technique)

Proton transfer reaction time-of-flight mass spectrometry

Proton transfer reaction, PTR

Proton transfer reactions aryl nitroalkanes

Proton transfer reactions constants

Proton transfer reactions hyperconjugation effects

Proton transfer reactions in the excited state

Proton transfer reactions in water

Proton transfer reactions reaction coordinate diagram

Proton transfer reactions sodium hydroxide

Proton transfer reactions, path-integral

Proton transfer secondary reactions

Proton transfer, chain reactions

Proton- and ion-transfer reactions

Proton-couple electron-transfer reactions

Proton-coupled electron transfer concerted reaction mechanism

Proton-coupled electron-transfer reactions

Proton-electron transfer reaction

Proton-transfer process, reaction

Proton-transfer reaction pathways

Proton-transfer reaction strengths

Proton-transfer reactions Borgis-Hynes model

Proton-transfer reactions Dogonadze, Kuznetsov, and Levich

Proton-transfer reactions Lee—Hynes model

Proton-transfer reactions benzophenone

Proton-transfer reactions benzophenone/?/, /-dimethylaniline

Proton-transfer reactions classical model

Proton-transfer reactions complexes

Proton-transfer reactions energetics

Proton-transfer reactions generalization

Proton-transfer reactions kinetics

Proton-transfer reactions mechanism

Proton-transfer reactions model

Proton-transfer reactions photochemistry

Proton-transfer reactions rates and mechanisms

Proton-transfer reactions semiclassical model

Proton-transfer reactions semiclassical/quantum model

Proton-transfer reactions solvent dynamics

Proton-transfer reactions tunneling mechanisms

Proton-transfer-reaction mass environmental applications

Proton-transfer-reaction mass human breath

Proton-transfer-reaction mass intermediates

Proton-transfer-reaction mass medical applications

Protonation Reactions

Protonation, electron-transfer reactions

Quantum proton transfer reaction

Rate constants proton transfer reactions

Rates of proton transfer reactions

Rates, equilibria, and structures in proton-transfer reactions

Reaction Path Specific Wavepacket Dynamics in Double Proton Transfer Molecules

Reactions hydrogen/proton transfer

Reactions involving single proton transfer

Reactions involving two proton transfers

Real proton transfer reaction mass

SN2 and Proton-Transfer Reactions

Specific Solute-Solvent Interactions and Proton Transfer Reactions

Study 5.1 Mechanistic photochemistry adiabatic proton transfer reactions of 2-naphthol and 4-hydroxyacetophenone

The Tunnelling Mechanism in Proton Transfer Reactions

Theoretical Aspects of Proton Transfer Reactions in a Polar Environment

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