Acceptors potential energy curve

In a similar fashion the bonding in H2 might be formally regarded as a complementary pair of one-electron donor-acceptor interactions, one in the ot (spin up ) and the other in the 3 (spin down ) spin set.8 In the long-range diradical or spin-polarized portion of the potential-energy curve, the electrons of ot and (3 spin are localized on opposite atoms (say, at on HA and 3 on HB), in accordance with the asymptotic dissociation into neutral atoms. However as R diminishes, the ot electron begins to delocalize into the vacant lsB(a) spin-orbital on HB, while (3 simultaneously delocalizes into Isa on HA, until the ot and (3 occupancies on each atom become equalized near R = 1.4 A, as shown in Fig. 3.3. These one-electron delocalizations are formally very similar to the two-electron ( dative ) delocalizations discussed in Chapter 2, and they culminate as before (cf. Fig. 2.9) in an ionic-covalent transition to a completely delocalized two-center spin distribution at... 

Figure 4.71 The potential-energy curve for the Ti- C2H4 insertion reaction (4.103) (circles, solid line), with leading long-range donor-acceptor interactions of nTi->-7Tcc+ (triangles, dotted line) and ncc n-rF (crosses, dashed line) types. (.R is the distance from Ti to the midpoint of C2.)...

Let us examine the balance between steric and donor-acceptor forces in greater detail for the case of HF- HF. The graph below plots the adiabatic potential-energy curve for H-bond formation (solid line, circles), as well as the steric repulsion energy37 (dotted line)... 

Figure 5.11 The adiabatic potential-energy curve for F HF hydrogen-bond formation (solid line, circles), with the steric repulsion energy (dotted line) and estimated np - oi ip donor-acceptor attraction (dashed line) included for comparison.

Order-disorder phase transitions are especially common in crystalline 7T-donor acceptor complexes between planar polycyclic aromatic hydrocarbons and other organic compounds. The disordered phase can sometimes be characterized in terms of either a static- or a dynamic-disorder model, as shown in Figure 13.2. The dynamic-disorder model consists of disordered components in motion within the confines of a broad well in the potential energy curve, whereas the static disorder model requires that the disordered components be localized in two or more sites in the asymmetric unit, within one or another of the wells of a multiwell-potential energy curve. When the possible sites for static disorder are not resolved by the effective resolution of the data set, it is difficult to choose between these models. This turned out to be true for an anthracene-tetracyanobenzene complex studied at several temperatures above and below the transition temperature Tj, of 206 It was found ° ° ... 

Figure 5.2 Left potential energy curves for an electron transfer reaction in an encounter complex of an acceptor A and a donor D, (A--D) — (A --D + ). Right rate constants predicted by combining Equations 5.6 and 5.7. The diagrams are explained in the text...

Subsequent transformations of the above H complexes are affected by a way of temperature or reactant concentration enhancement as well as by addition of the third donor or acceptor component (catalyst) [4,47,48]. Quantum chemical computations of a section of potential energies surface along the reaction pathway for some Sgi and SNi processes with silica OH group reveal that the linear H-complex with this group formed in the first reaction stage reactions thereafter transform to a cyclic donor-acceptor complex. The second minimum on the potential curve (Fig. 1) is due to formation of a cyclic donor-acceptor complex (DAr) which is recognized for SeJ and SnI reactions [49]. 

Figure 9.10. Diabatic free energy curves illustrating (a) photoinduced ET reaction and (b) back ET reaction in a ID solvation coordinate system. A resonant optical pulse brings a stationary nuclear wave packet from the ground potential surface to the donor surface, where it relaxes toward equilibrium with concomitant ET to the acceptor state.

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