Energy Profile of protonation

The spectroscopic, kinetic, and thermodynamic data discussed are sufficient to describe semiquantitatively the energy profile of proton transfer to a hydride ligand occurring in solution [29, 35, 36]. Figure 10.10 shows the energy as a function of the proton-hydride distance, varying from the initial state to a final product. The average structural parameters of the initial hydrides and intermediates have been taken from earlier chapters. Since proton-hydride contacts of... 

Figure 10.10 Energy profiles of proton transfer to a hydride ligand of a transition metal complex in solution AEi = + 3 to 4kcal/mol, AE2 = — 5 to — 7 kcal/mol, A 3= + 10 to 14 kcal/mol, and A 4 = —7 kcal/mol the energy is a function of the proton-hydride distance, varying from an initial state (2.5 A) to the final product (0.9 A) conversion of the intimate ion pair to the solvent-separated ion pair is shown as a function of the H+- O" distance. (Reproduced with permission from ref. 29.)...

Fig. 5.17 Energy profile of proton transfer in mAMP-H7 tautomer (B3LYP/aug-cc-pvdz)...

Fig. 16. Energy profiles of the protonation and propagation reactions of ethene in the gas phase and in solution (CH2C12) starting with 4 monomer units and a free proton...

Ah initio calculations to map out the gas-phase activation free energy profiles of the reactions of trimethyl phosphate (TMP) (246) with three nucleophiles, HO, MeO and F have been carried out. The calculations revealed, inter alia, a novel activation free-energy pathway for HO attack on TMP in the gas phase in which initial addition at phosphorus is followed by pseudorotation and subsequent elimination with simultaneous intramolecular proton transfer. Ah initio calculations and continuum dielectric methods have been employed to map out the lowest activation free-energy profiles for the alkaline hydrolysis of a five-membered cyclic phosphate, methyl ethylene phosphate (247), its acyclic analogue, trimethyl phosphate (246), and its six-membered ring counterpart, methyl propylene phosphate (248). The rate-limiting step for the three reactions was found to be hydroxyl ion attack at the phosphorus atom of the triester. ... 

Figure 16.8. Calculated energy profile of the Bergman cychzation of imine 120 and its protonated form 120—and of the subsequent refro-Bergman cychzation to nitrile 108 (108-H+). ...

Figure 6.8. Gibbs energy profiles of a proton discharge process resulting in a metal-hydrogen bond formation. The difference in the Gibbs energy of adsorption of hydrogen between metal 1 to metal 2 lowers the activation barrier for the discharge and makes metal 2 the electrocatalytically more favorable (active) electrode material.

Here erf, and erf are the Pauli matrices, that act on the proton (deuteron) wavefunctions potential wells of the proton (deuteron) potential energy profile of the th H-bond (in accordance with the available diffraction data the short H-bonds O-H- O with two off-center sites of a proton are considered). The parameters of Hamiltonian (1), i.e., the tunneling parameter Cl and the Ising parameters J,p describe the motion of a proton (deuteron) along H-bond and the effective pair interactions of these particles, respectively. When Cl is substantially smaller than Jy the static approximation (Cl = 0) becomes valid. Instead of equation (1) one has in this case... 

For a theoretical (ab initio) study of the potential energy profile for proton transfer from NH4 to NH3, see Delpuech et al, 1972. 

Chu, C.-H., and Ho, J.-J., Effect of formaldehyde substituents on potential energy profiles for proton transfer in [ABCO-HOCXHff, J. Phys. Chem. 99, 16590-16596 (1995). 

Figure 1 illustrates the free energy profile of a typical acid-catalyzed chemical reaction that converts a substrate S to a product P. In this case, an intermediate chemical species SH+ is formed on protonation of S. If the activation energy for conversion of SH+ to PH+ is lower than for the conversion of S to P, then the reaction will go faster. It is important at this point to define the difference between an intermediate and a transition state An intermediate is a stable (or semistable) chemical species formed during the reaction and therefore is a local energy minimum, whereas a transition state, by definition, is a local energy maximum. 

Figure 4. a) Free energy profiles of the protonated mechanism with a total charge of -2 on the reacting fragments The upper curve is the uncatalyzed reference reaction in water... 

FIGURE 4. Possible types of IHB potential energy profiles in proton sponge cations... 

Figure 3 Energy profiles for proton transfer in the C1H... H20 complex. The effect of environment is accounted for by the Onsager model with different values of the solvent dielectric constant e...

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