Enthalpy values phosphinic acid

The measure of basicity of phosphine hgands most widely quoted in the hterature is p/fa (aqueous), which is a measure of Bronsted basicity or proton affinity. A selection of pA a values for various phosphines is given in Table 4. AngeUci and coworkers have established a method for determining proton affinities from enthalpies of protonation using the extremely powerful acid CF3SO3H. The enthalpy values (A//hp) and pATa values are related by the empirical equation (3) ... 

The dimensionless acceptor number, AN, ranked the acidity of a solvent and was defined for an acidic solvent A as the relative P NMR downfield shift (A3) induced in triethyl phosphine when dissolved in pure A. A value of 0 was assigned to the shift produced by the neutral solvent hexane, and a value of 100 to the shift produced by SbClj. Gutmann suggested that the enthalpy of acid-base adduct formation be written as ... 

In the course of this study, the authors determined j6-values for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The )8-scales are applied to the various reactions or the spectral measurements. The /1-scales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /1-scale, family-independent (FI) types. Consequently, a variety of )8-scales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is 7 = 0.983. Several averaged scales are shown in Table 15 . 

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