Single-Proton Transfer

The mechanism includes two single electron transfers (steps 1 and 3) and two proton transfers (steps 2 and 4) Experimental evidence indicates that step 2 is rate determining and it is believed that the observed trans stereochemistry reflects the dis tribution of the two stereoisomeric alkenyl radical intermediates formed in this step... 

The mechanism by which the Birch reduction of benzene takes place (Figure 118) IS analogous to the mechanism for the metal-ammonia reduction of alkynes It involves a sequence of four steps m which steps 1 and 3 are single electron transfers from the metal and steps 2 and 4 are proton transfers from the alcohol... 

The proton transfer equilibrium that interconverts a carbonyl compound and its enol can be catalyzed by bases as well as by acids Figure 18 3 illustrates the roles of hydroxide ion and water m a base catalyzed enolization As m acid catalyzed enolization protons are transferred sequentially rather than m a single step First (step 1) the base abstracts a proton from the a carbon atom to yield an anion This anion is a resonance stabilized species Its negative charge is shared by the a carbon atom and the carbonyl oxygen... 

DFT STUDY OF 8-MERCAPTOQUINOLINE INTRAMOLECULAR HYDROGEN BOND, SINGLE PROTON TRANSFER AND WATER-ASSISTED TAUTOMERIZATION... 

The Variation of J with Temperature. Although each proton transfer has its own characteristic value of 0, the variation of K near the maximum shows a marked degree of uniformity, as already mentioned in Sec. 64. If a parabola of the form p(T — 0)2 is fitted to the experimental results, a single value of p, namely 5 X 10-6, reproduces the variation of log K, not only for proton transfers of class III, but also for those of class II and class IV. If we accept (140) as providing a qualitative theory of the phenomena, we have at once a physical explanation of the observed uniformity. Whether we are concerned with the... 

The addition of the anions of racemic cyclic allylic sulfoxides to various substituted 2-cyclopentenones gives y-l,4-adducts as single diastereomeric products22. The modest yields were due to competing proton-transfer reactions between the anion and enone. The stereochemical sense of these reactions is identical to that for the 1,4-addition reaction of (Z)-l-(/erf-butylsulfinyl)-2-methyl-2-butene to 2-cyclopentenone described earlier. 

A. A Simplified EVB Calculation of a Proton Transfer between Cysteine and Histidine in Water. (The reaction is represented in an oversimplified way by assigning all the histidine residual charges to a single nitrogen)... 

Like all chemical equilibria, this equilibrium is dynamic and we should think of protons as ceaselessly exchanging between HCN and H20 molecules, with a constant but low concentration of CN and H30+ ions. The proton transfer reaction of a strong acid, such as HCl, in water is also dynamic, but the equilibrium lies so strongly in favor of products that we represent it just by its forward reaction with a single arrow. 

A hydrogen cation is a hydrogen atom that has lost its single electron, leaving a bare hydrogen nucleus. A bare hydrogen nucleus is a proton. Thus, any reaction in which H moves from one species to another is called a proton-transfer reaction. Protons readily form chemical bonds. In aqueous solution, they associate with water molecules to form hydronium ions. 

Dinitrophenol (DNP) gives a single wave in NPV and a pair of anodic and cathodic peak currents in CV at the NB/W interface in pH range studied. Figure 7 shows a cyclic voltammogram of 0.6 mM DNP (NB) at O.IM TPenATPB (NB)-O.IM LiCl, 50 mM phosphate buffer, pH 6.3 (W), that can be assigned to one-proton transfer assisted by A present in NB. The E]j2 vs. pH plot is shown in Fig. 8, in which the results obtained with... 

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