Mechanisms, of proton transfer between

Since the domain explored will always be a very small part of the possible cases of tautomerism, it is essential to have general rules for families of compounds, substituents, and solvents. This chemical approach is maintained in this chapter, although the importance of the calculations is recognized. The following discussion begins with calculation of tautomeric equilibrium constants, followed by the combined use of theoretical calculations and experimental results (an increasingly expanding field) and ends with the calculations of the mechanisms of proton transfer between tautomers. 

Acids and bases, oxygen and nitrogen in aqueous solution, mechanisms of proton transfer between, 22, 113... 

Mechanisms of Proton Transfer between Oxygen and Nitrogen Acids and Bases in Aqueous Solution... 

In the case of non-HBD solvents, such as DMSO, the measured pK values are absolute (that is, free from ion pairing) and can be directly compared with gas-phase acidities6 in addition, knowledge of the heats of ionization in DMSO7 allows the evaluation of a possible entropy effect when the two phases are compared. The mechanism of proton transfer between oxygen and nitrogen acids and bases in aqueous solution has been reviewed8. 

Abstraction, hydrogen atom, from O—H bonds, 9, 127 Acid-base behaviour macroeycles and other concave structures, 30, 63 Acid-base properties of electronically excited states of organic molecules, 12, 131 Acid solutions, strong, spectroscopic observation of alkylcarbonium ions in, 4, 305 Acids, reactions of aliphatic diazo compounds with, 5, 331 Acids, strong aqueous, protonation and solvation in, 13, 83 Acids and bases, oxygen and nitrogen in aqueous solution, mechanisms of proton transfer between, 22, 113... 

Mechanisms, of proton transfer between oxygen and nitrogen acids and bases in aqueous solutions, 22, 113 Mechanisms, organic reaction, isotopes and, 2, 1 Mechanisms of reaction, in solution, entropies of activation and, 1, 1 Mechanisms of reaction, of /3-lactam antibiotics, 23, 165 Mechanisms of solvolytic reactions, medium effects on the rates and, 14, 10 Mechanistic analysis, perspectives in modern voltammeter basic concepts and, 32, 1 Mechanistic applications of the reactivity-selectivity principle, 14, 69 Mechanistic studies, heat capacities of activation and their use, 5, 121 Mechanistic studies on enzyme-catalyzed phosphoryl transfer, 40, 49 Medium effects on the rates and mechanisms of solvolytic reactions, 14, 1 Meisenheimer complexes, 7, 211... 

Acid solutions, strong, spectroscopic observation of alkylcarbonium ions in, 4, 305 Acid-base properties of electronically excited states of organic molecules, 12, 131 Acids and bases, oxygen and nitrogen in aqueous solution, mechanisms of proton transfer between, 22, 113... 

Polarisation of the substrate carbonyl group appears to be achieved in yet a third way by mammalian glucose 6-phosphate isomerase, which interconverts glucose and fructose 6-phosphates, The crystal structure of the rabbit enzyme in complex with the reactive intermediate analogue o-arabinohydroxamic acid Ki = 0.2 pM) (in its hydroximic form) reveals a cluster of four water molecules hydrogen bonded to each other, to the counterparts of 01 and 02 of the enediolate intermediate and to an active site arginine. Grotthus mechanisms of proton transfer between the two tautomers of the enediolate probably occur. 

The fiuorescein molecule is a suitable model system for monitoring the mechanism of proton transfer between adjacent sites as it has two distinct proton binding sites 6 A apart, each having a distinct pK and spectral properties. The first is the oxyanion attached to the xanthene ring, whose protonation is associated with a spectral shift of the dye, while the second is the carboxylate on the benzene ring. The protonation of this site has no effect on the absorption spectrum of the dye (Scheme 20.1). 

O., Nachliel, E., Gutman, M., The mechanism of proton transfer between adjacent sites exposed to... 

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