Proton transfer linear

No proton transfers were observed in linear oligomers (catemers) of pyrazoles 8 in the solid, a fact which was understandable because such rearrangements would require a very high activation energy [97JCS(P2)101]. A possible exception to this rule is a catemer 8f, for which slow proton transfer was observed in the solid state [97JCS(P2)1867]. 

Due to the perfect linear arrangement of the N-H -N hydrogen bridges in 13, extremely fast cooperative proton transfers occur in solution which... 

If any equilibrium constants show this linearity, this behavior is most likely to be found among proton transfers of type (118) and type (120). The expressions for log K given in Table 11 show this linearity they represent, within the experimental error, the accurate data obtained by measurements on three proton transfers in aqueous solution. All three are of the type (120). 

An interesting point that emerges from Fig. 5.6 is the relation between Ag and (AAgsol)w. p. As seen from the figure, the lowering of the activation energy for the reaction is almost linearly proportional to the stabilization of the ionic resonance form (AAg )w. p. An enzyme which is designed to accelerate a proton transfer between A and B will simply stabilize the (B 1—H A-) state more than water. 

The activation energy for the charge reduction reaction is due to two factors the bond stretching and distortions of the originally near linear complex, so as to achieve the internal proton transfer and the increase of energy due to the Coulombic repulsion between the two charged products, a repulsion that leads to a release of kinetic energy on their separation. 

Large numbers of reactions of interest to chemists only take place in strongly acidic or strongly basic media. Many, if not most, of these reactions involve proton transfer processes, and for a complete description of the reaction the acidities or basicities of the proton transfer sites have to be determined or estimated. These quantities are also of interest in their own right, for the information available from the numbers via linear free energy relationships (LFERs), and for other reasons. 

The crucial step in self-alkylation is decomposition of the butoxy group into a free Brpnsted acid site and isobutylene (proton transfer from the Fbutyl cation to the zeolite). Isobutylene will react with another t-butyl cation to form an isooctyl cation. At the same time, a feed alkene repeats the initiation step to form a secondary alkyl cation, which after accepting a hydride gives the Fbutyl cation and an -alkane. The overall reaction with a linear alkene CnH2n as the feed is summarized in reaction (10) ... 

In recent years, evidence has been found that both mechanisms of proton transfer can occur for certain intramolecularly hydrogen-bonded acids. Also, new kinetic behaviour has been obtained which allows a much more detailed examination of the reaction steps in (22). Kinetic data for the second ionization of substituted phenylazoresorcinols in the presence of hydroxide ions (25) were some of the first to be obtained for an intramolecularly hydrogen-bonded acid. The reciprocal relaxation time (t ) for the approach to equilibrium in a temperature-jump experiment was measured at different hydroxide-ion concentrations. A linear dependence of x on [OH] was obtained of the form of (26) (Eigen and Kruse, 1963 Inskeep et al., 1968 Rose and Stuehr, 1971). However, careful measurements at lower hydroxide-ion concentrations (Perlmutter-Hayman and Shinar, 1975 Perl-mutter-Hayman et al., 1976 Yoshida and Fujimoto, 1977) revealed that the... 

Of hundreds of theoretically possible pathways, the list can be trimmed to four using linear sweep voltammetry (LSV) and chemical arguments [22]. The LSV method is an exceptionally powerful one for analyzing electrochemical processes [24-27]. From LSV studies, it was concluded that a single heterogeneous electron transfer precedes the rate-determining step, cyclization is first order in substrate, and that proton transfer occurs before or in the rate-determining step. The candidates include (a) e-c-P-d-p (radical anion closure). 

From the thermodynamics of such dynamical hydrogen bonds , one may actually expect an activation enthalpy of long-range proton diffusion of not more than 0.15 eV, provided that the configuration O—H "0 is linear, for which the proton-transfer barrier vanishes at 0/0 distances of less than 250 pm. However, the mobility of protonic defects in cubic perovskite-type oxides has activation enthalpies on the order of 0.4—0.6 eV. This raises the question as to which interactions control the activation enthalpy of proton transfer. 

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