Proton transfer reactions reaction coordinate diagram

Figure 5.35 displays a schematic energy-level diagram for each stationary species along the proton-transfer reaction coordinate. Although Pauling bond strengths... 

Figure 5.35 A schematic energy-level diagram for key stationary points along the H2 + HO+ HOH proton-transfer reaction coordinate.

FIGURE 2. Tridimensional reaction coordinate diagram for the hydrolysis of I-X-4-Z-2.6-dinitrobenzene. The. v-axis represents the proton transfer reaction and the y-axis, the C—O bond formation78. Reproduced by permission of the Indian Journal of Technology... 

Fig. 16 Free energy/reaction coordinate diagram for proton transfer from the 4,6-bis(phenylazo)resorcinol monoanion to give the dianion in the presence of 2-methylphenol buffers at a 1 1 buffer ratio and at buffer concentrations of (a) 0.001 and (b) 0.10mol" dm. ...

Figure 8.4 Reaction coordinate diagram for the proton transfer HX + Y HY, where HX is a weaker acid than HY.

Fig. 1. Reaction coordinate diagram showing rate-limiting attack of water on an amide to give intermediate II which rapidly transfers a proton to solvent water to give III or IV.

In Chapter 4, we introduced reaction mechanisms and reaction coordinate diagrams. These concepts were explained in the context of acid-base chemistry, which involves the transfer of a proton from one chemical entity to another occurring in a single step. Although many chemical transformations take place in one step, many others involve... 

Figure 9.13 depicts reaction coordinate diagrams for different mechanisms. Assume that each of these reactions involves a nucleophilic addition (e.g. to a carbonyl or acyl group) and a proton transfer. We will examine several such reactions in Chapter 10. 

We have made use above of the idea that the magnitude of a (or / ) measures the extent of proton transfer at the transition state or, equivalently, of the position of the transition state along the proton-transfer reaction coordinate. Figures 8.4 and 8.5 show, respectively, the reaction coordinate diagrams drawn according to the Hammond postulate for Reaction 8.17 in the extreme cases where HX is a... 

Fig. 1 More O Ferrall-Jencks diagram for the deprotonation of a nitroalkane. The curved line shows the reaction coordinate with charge delocalization lagging behind proton transfer.

He concludes that, in the transition state for the acid-catalysed reaction, proton A is half transferred, protons B and C have not moved and the C- -O bond is partially formed. In discussing in a complex reaction whether the different atom transfers are concerted or take place in a series of discrete steps, it is helpful to use contour diagrams depicting the reaction coordinate as a function of two geometrical variables. These diagrams were introduced to describe the role of the... 

H2O. Moreover, the half-reactions in aqueous solution exhibit a pH dependence corresponding to the addition of one proton in conjunction with each electron. Thus, under the conditions of Fig. 12, the [Mn2 O2] center (1) is converted to an [Mn2 O(OH)]5+ center (2) in the first reduction and to an [Mn2 (OH)2] center (3) in the second. Electrode half-reactions, Nernst equations, and pA a values for the phen complex and for several related systems are summarized in Table 5. Precise data are somewhat difficult to obtain for these systems owing to the slow electron-transfer kinetics (fcgj, 10 cm s or less), the need to activate the working electrode surface to achieve a useful response, and the limited stability of some species in the presence of coordinating buffers. Nonetheless, pAa values for the bpy complex obtained from the Pourbaix diagram in Ref. 93 lead to pH-independent potentials of +1.1 and +0.5 V, respectively, for [Mn2 O(OH)]3+ and [Mn2 O2] + reduction, values that compare reasonably well to the results in Table 4, given the difference in solvent environments. 

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