Gutmann solvent donor number

The half-wave potentials for the Fe(III)/ Fe(II) reaction of (TPP)FeX varied little as a function of the counteranion in DMSO or Py, and this was accounted for by a displacement of the halide axial ligand by a bound solvent molecule leading to [(TPP)Fe" (S)2]+ and (TPP)Fe"(S)2 in solution, where S = DMSO or Py. The effect of solvation on the Fe(III)/Fe(II) reaction of (TPP)FeX was quantitated by Bottom-ley and Radish who correlated E1/2 values for reduction with the Gutmann solvent donor number [187]. Half-wave potentials... 

Donor strengths, taken from ref. 207b, based upon the solvent effect on the symmetric stretching frequency of the soft Lewis acid HgBr2. Gutmann s donor number taken from ref 207b, based upon AHr for the process of coordination of an isolated solvent molecule to the moderately hard SbCL molecule in dichioroethane. ° Bulk donor number calculated as described in ref 209 from the solvent effect on the adsorption spectrum of VO(acac)2. Taken from ref 58, based on the NMR chemical shift of triethylphosphine oxide in the respective pure solvent. Taken from ref 61, based on the solvatochromic shift of a pyridinium-A-phenoxide betaine dye. 

One of them is Gutmann s donor number, DN, (Gutman and Vychera 1966) defined as the negative of the standard molar heat of reaction (expressed in kcal mol 1, 1 cal = 4.184 J) of the solvent with antimony pentachloride to give the 1 1 complex, when both are in dilute solution in the inert diluent 1,2-dichloroethane. This quantity needs to be determined calorimetrically, as was done for a considerable number of solvents at that time (Gutman and Vychera 1966). There are several problems with the DN scale. One is the fact that calorimetric equipment... 

DN solvent donor number (Gutmann) [= -AiT(D—SbCls)] kcal mol ... 

A series of silanol and silylamine chemical shifts were obtained in various solvents. (83) The silanols are found to be highly dependent (>5ppm shifts) upon solvent basicity with the more basic solvents causing low frequency shifts. This shielding effect is found to give an excellent linear correlation with Gutmann s donor number (DM) (130) which is a measure of the electron pair donor ability of the solvent. Figure 23 shows the correlation for five of the compounds examined. It... 

The Gutmann s Donor Number (DN) was proposed [Gutmann, 1978] as a quantitative empirical parameter for solvent nueleophilicity. For most solvents it was found to correlate well with the p scale. 

Much attention has been given to correlating A// against properties of the interacting species. Two of the most common are the Gutmann [96] donor number, DN, or acceptor number, AN, scales and the Drago [97] E C formulation. The donor number, DN, quantifies the Lewis basicity of a variety of solvents and was defined for a given base B as the exothermic heat of its reaction with the reference acid, antimony pentachloride, in a 10 - M solution in a neutral solvent (1,2-dichloroethane). The units are (kJ/mol). Specifically ... 

Tfaeie have been a number of attempts to develop solvent parameter scales that could be used to correlate ttiermodynamic and kinetic results in terms of these patametois. Gutmann s Donor Numbers, discussed previously, are sometimes used as a solvent property scale. Kamlet and Taft and co-workers developed the solvatochromic parameters, Uj, B, and n that are related to the hydrogen bonding acidity, basicity and polarity, respectively, of the solvent. Correlations with these parameters also use the square of tte Hildebrand solubility parameter, (5, that gives the solvent cohesive energy density. Parameters for some common solvents are collected in Table 3.6. 

Donating solvents such as hexamethylphos-phoramide or dimethylpropylurea give rise to upheld shifts which have been interpreted as caused by the formation of pentacoordinated complexes. The solvents shifts seem to follow Gutmann s donor number for solvents. 

The chemistry of Lewis acid-base adducts (electron-pair donor-acceptor complexes) has stimulated the development of measures of the Lewis basicity of solvents. Jensen and Persson have reviewed these. Gutmann defined the donor number (DN) as the negative of the enthalpy change (in kcal moL ) for the interaction of an electron-pair donor with SbCls in a dilute solution in dichloroethane. DN has been widely used to correlate complexing data, but side reactions can lead to inaccurate DN values for some solvents. Maria and Gal measured the enthalpy change of this reaction... 

The best-known solvent parameters are the donor number [21] and acceptor number [22] proposed by Gutmann and coworkers. The donor number (DN) for a donor solvent D is defined as the positive value of the enthalpy difference AH (kcalmol ) for the reaction of D with an acceptor-halide SbCls (D + SbCls D SbCls) in an inert medium such as 1,2-dichloroethane. DN is a fair measure for the donor properties of a solvent. The correlations of DN with the solvation energies are known to be good particularly for solvation of cations. A typical example [19] is shown in Fig. 3. 

The donor number, DN, of a solvent, proposed by Gutmann, is a measure of the Lewis basicity of the solvent, i.e. its ability to donate a pair of electrons [16]. The DN is determined by measuring the negative enthalpy for the reaction of equimolar quantities of the solvent with the standard Lewis acid, SbCls, at room temperature in 1,2-dichloroethane (Scheme 1.1), and reflects the ability of the solvent to solvate Lewis acids. SbCls reacts with protic solvents such as alcohols... 

Gutmann introduced3 the concepts of donor number (donicity) and acceptor number (acceptivity), as dimensionless numbers, for the characterization of donor properties of bases independently of the solvent. 

The enthalpy change during donor-acceptor adduct formation has been related by Drago to the sum of two terms (1) the product of the electrostatic properties of the acid and the base, Ef. and E and (2) the product of their tendency toward covalent bonding, Ca and Cb [10]. For the particular case, where the acceptor is specified to be SbCb (and the inert solvent is 1,2-dichloroethane), the negative of this enthalpy change (in kcal mol", 1 cal = 4.184 J) is the Gutmann donor number, DN [2,11]. These concepts are further discussed in Chapter 3. 

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