Energy profile diagram

A potential energy diagram for nng inversion m cyclohexane is shown m Figure 3 18 In the first step the chair conformation is converted to a skew boat which then proceeds to the inverted chair m the second step The skew boat conformation is an inter mediate in the process of ring inversion Unlike a transition state an intermediate is not a potential energy maximum but is a local minimum on the potential energy profile... 

Not all energy diagrams are like that shown for the reaction of ethylene and HBr. Each reaction has its own energy profile. Some reactions are fast (small AG ) and some are slow (large AG ) some have a negative AG", and some have a positive AG°. Figure 5.6 illustrates some different possibilities. 

When this correction is included, the reaction energy profile diagram results for the cationation and the first three propagation steps in the gas phase and in solution (Fig. 16). 

Fig. 18 Free energy profiles for the solvent extraction of copper, where L is Acorga P50. The profile shows the free energy of a site on the liquid/liquid interface. All higher-order rate constants are reduced to first-order rate constants by using the concentrations of reactants in either phase. The free energy lost in each cycle can be seen from the difference between 0 and the 10%, 50% and 80% extraction lines on the right of the diagram. The double-headed arrows indicate the rate-limiting free energy difference.

Fig. 3 Representative energy profile diagram for a single-step reaction.

A structure-structure correlation may itself contain some of the necessary information. Note that in Fig. 4 the points are most abundant in the regions where dx and d2 are about 1.0 and 1.5-2 A, respectively, and sparse close to the point where dt and d2 are equal. This distribution is expected if the symmetrical system is of higher energy, so that the energy profile diagram for the proton transfer reaction (5)... 

Fig. 13 Approximate energy profile diagram for the ring inversion reaction [73]—>[73 ] using the M-C2(C3) distance as the reaction coordinate (see text). The authors develop this picture considerably further. Reprinted with permission from Biirgi and Dubler-Steudle (1988a). Copyright 1988 American Chemical Society.

Figure Schematic diagram to show the reorganization energy for isotopic reactions for harmonic free energy profiles. Ci i, and Gf, represent the initial (reactant) and the final (product) system free energy respectively.

Figure 5. Schematic diagram to show the reorganization energy A, for nonisotopic reactions for Morse free energy profiles. This figure shows a normal region activation barrier when -AG° < A, an activationless situation when -AC° =, and no inverted region activation barrier when -AC° > A. When -AG° > A, the two free energy profiles do not cross, Cjni, and Gn represent the initial (reactant) and the final (product) system free energy, respectively.

Figure 5.1 Energy profile diagram transition state...

Graphical representation of the saddle point (here marked with an X) for the transfer of atom B as the substance A-B reacts with another species, C. Potential energy is plotted in the vertical direction. Note also that the surface resembles a horse saddle, with the horn of the saddle closest to the observer. As drawn here, the dissociation to form three discrete species (A + B J- C) requires much more energy than that needed to surmount the path that includes the saddle point. A two-dimensional "slice" through a saddle point diagram is typically called a reaction-coordinate diagram or potential-energy profile. 

E. Strategy Free energy profiles and difference energy diagrams... 

It is possible to use the 3-D surface with its corresponding 2-D contour diagram and potential energy profile to discuss the general reaction A + BC —> AB + C where A, AB, BC and C are all polyatomic molecules. 

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