Proton transfer free energy

Adiabatic Proton Transfer Free Energy Relationship (FER)... 

It frequently happens that a corner species is derived from a lower energy bond isomer by a proton transfer. The energy of such a proton transfer is calculated from the relevant pvalues, estimated where necessary by linear free energy relations.96... 

Standard electrode potentials of the Ag-AgI electrode were determined in the temperature range 5 °-35°C in 20-80 wt % ethylene glycol + diethylene glycol mixtures by emf measurements on the cell Pt-H2(g, 1 atm)/HOAC (mt), NaOAC (m2) KX (m3)/AgX-Ag in the solvent. The standard molal potentials Em°, in the various solvent mixtures have been expressed as a function of temperature. The various thermodynamic parameters for the transfer of hydrogen iodide from ethylene glycol to these media at 25° C are reported, and their variation with solvent composition is discussed. The transfer free energies of the proton and the iodide at 25°C, on the basis of the ferrocene reference method with ethylene glycol as the reference solvent, are also reported in the mixtures. 

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.

Outer sphere electron transfer (e.g., [11-19,107,160-162]), ion transfer [10,109,163,164] and proton transfer [165] are among the reactions near electrodes and the hquid/liquid interface which have been studied by computer simulation. Much of this work has been reviewed recently [64,111,125,126] and will not be repeated here. All studies involve the calculation of a free energy profile as a function of a spatial or a collective solvent coordinate. 

If in a dilute solution we carry out q proton transfers according to (28), there will be a change in the cratic term, and at the same time the free energy will receive the contribution qj, that is to say, q units each equal to J Since each of the quantities qD, qL, qY, and qj consists of q equal units, we may call them unitary quantities, in contrast to the cratic term, which is a communal quantity, depending as it does on the amount of solvent as well as the amount of solute present. 

Heat of Precipitation. Entropy of Solution and Partial Molal Entropy. The Unitary Part of the Entropy. Equilibrium in Proton Transfers. Equilibrium in Any Process. The Unitary Part of a Free Energy Change. The Conventional Standard Free Energy Change. Proton Transfers Involving a Solvent Molecule. The Conventional Standard Free Energy of Solution. The Disparity of a Solution. The E.M.F. of Galvanic Cells. 

In electrochemistry the symbol AF is used to denote the value per mole, not the value per particle. To avoid confusion, we shall use dF/dn to denote the change in the free energy per proton transferred then we shall call (70) the cratic part of dF/dn for the proton transfer. 

The Number of Dipoles per Unit Volume. The Entropy Change Accompanying Proton Transfers. The Equilibrium between a Solid and Its Saturated Solution. Examples of Values of L and AF°. The Change of Solubility with Temperature. Uni-divalent and Other Solutes. Lithium Carbonate in Aqueous Solution. H2COj in Aqueous Solution. Comparison between HjCOj and Li2C03 in Aqueous Solution. Heats of Solution and the Conventional Free Energies and Entropies of Solution. 

For coupling with 2-naphthol-6,8-disulphonic-l-isotope effects (kK/kD) varied with the substituent in the benzenediazonium ion as follows 4-C1 (6.55) 3-C1 (5.48) 4-N02 (4.78), i.e. the reactivity of the ion was increased so that i correspondingly decreased. Base catalysis was observed127, 129, and there was a free energy relationship between this catalytic effect and the basicity of pyridine, 3- and 4-picoline. However, for 2-picoline and 2,6-lutidine, the catalysis was 3 times and 10 times less than expected from their basicities showing that, in this particular proton transfer, steric hindrance is important. 

The approach presented above is referred to as the empirical valence bond (EVB) method (Ref. 6). This approach exploits the simple physical picture of the VB model which allows for a convenient representation of the diagonal matrix elements by classical force fields and convenient incorporation of realistic solvent models in the solute Hamiltonian. A key point about the EVB method is its unique calibration using well-defined experimental information. That is, after evaluating the free-energy surface with the initial parameter a , we can use conveniently the fact that the free energy of the proton transfer reaction is given by... 

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