Potential energy proton transfer

Recent studies show that the inclusion of correlation energy does considerably influence the potential energy data especially in search of DM potentials for proton transfer. 

FIGURE 4 7 Potential energy diagram for proton transfer from hydrogen chio ride to tert butyl alcohol... 

Three-dimensional potential energy diagrams of the type discussed in connection with the variable E2 transition state theory for elimination reactions can be used to consider structural effects on the reactivity of carbonyl compounds and the tetrahedral intermediates involved in carbonyl-group reactions. Many of these reactions involve the formation or breaking of two separate bonds. This is the case in the first stage of acetal hydrolysis, which involves both a proton transfer and breaking of a C—O bond. The overall reaction might take place in several ways. There are two mechanistic extremes ... 

Fig. 8.3. Three-dimensional potential energy diagram for addition of a proton and nucleophile to a caibonyl group, (a) Proton transfer complete before nucleophilic addition begins (b) nucleophilic addition complete before proton transfer begins (c) concerted proton transfer and nucleophilic addition.

Which proton transfer is easier energetically, Q —> QH or QH- QH2 (The energy of H is given at right.) Use electrostatic potential maps of Q and QH anion (QH ) to explain this difference. 

Let the initial distance between the particles AH and B be denoted by r. The mutual potential energy of the two charged particles is —c2/r, as in the simple ionic dissociation depicted in Fig. 8a. If the value of r is sufficiently great, the energy associated with the electrostatic fields will not depend appreciably on r. For the proton transfer there is thus a characteristic quantity similar to D or. 

Figure 2.9 Model potential energy surface for combined electron and proton transfer. is the solvent coordinate for electron transfer and Q2 that for proton transfer. (See color insert.)...

Based on the theoretical electrochemistry method outlined above in combination with DFT calculations, the potential energy of the intermediates can be obtained at a given potential, (Fig. 3.5). Since aU steps involve exactly one proton and electron transfer, the height of the different steps scales directly with the potential. To calculate the potential energy landscape at the equilibrium potential, the levels are moved down hyn X 1.23 eV, where n is the number of the electrons at the given state (the horizontal axis in Fig. 3.5). 

Figure 2.10 Potential energy surface for combined electron and proton transfer.

Figure 5-3. Active site and calculated PES properties for the reactions studied, with the transferring hydrogen labelled as Hp (a) hydride transfer in LADH, (b) proton transfer in MADH and (c) hydrogen atom transfer in SLO-1. (i) potential energy, (ii) vibrationally adiabatic potential energy, (iii) RTE at 300K and (iv) total reaction path curvature. Reproduced with permission from reference [81]. Copyright Elsevier 2002...

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