Donor number table

Oxyhalides with Low Donor Numbers Table 49. Formation Constants K of [(C6H5)3C]+[MCln+i]-in Benzoyl Chloride at 20° ... 

Table 1.6 Dipole moments (p.), dielectric constants (er), normalized donor numbers (DNn) and acceptor numbers (AN) for some common solvents [1,2]...

A third method of estimating solvent basicity is provided by the donor number concept 14 ). The donor number of a solvent is the enthalpy of reaction, measured in kcal per mole, between the solvent and a Lewis add such as antimony (V) chloride. (Other Lewis acids, such as iodine or trimethyltin chloride, may be used, but the scale most often reported is that for SbCl5.) Available values for the SbCls donor number have been included in Table 1. Plots of the Walden product versus solvent basicity (A//SbC1 ) for several solvents are shown for lithium, sodium, and potassium ions in Fig. 10 and for the tetraalkylammon-... 

The ability of molecules to accept a hydrogen bond is measured by the Taft-Kamlet solvatochromic parameter, P, (or P for the monomer of self-associat-ing solutes) (see Table 2.3). This, too, is a measure of their basicity (in the Lewis sense), also measured by the Gutmann donor number DN (discussed later). Thus, pyridine has P = 0.64, compared with 0.40 for acetonitrile, but... 

Solvation and Solvent Phenomena 59 Table 3.7. Donor numbers of some solvents. 

These donor numbers provide an interesting comparison of the relative donor abilities of the various solvents (Table 10.4). ranging from the practically nonpolar 1,2-dichloroethane to the highly polar hexamethylphosphoramide. ((CHdjNIjPO. Note, however, that there is no exact correlation between donor number and permittivity. Some solvents with relatively high permittivities such as mtromethane and propylene carbonate (e/e = 38.6 and 65.1) may be very poor donors (DN — 2.7 and 15.1). Conversely, the best donors do not always have high permittivities pyridine (DN -33.1. e/e0 = 12.3) and diethyl ether (DN = 19.2. e/% = 4.3). This should serve lo remind us that solubility is not merely an electrostatic interaction but that solvation also involves the ability to form covalent donor bonds. Note that pyridine may be considered to be a relatively soft base (Chapter 9). Gulmann has extended the concept... 

TABLE 7.2 Donor Number, DNSbCu of Some Organic Solvents... 

Cu(acac)(tmen)]BPh4, is known to provide a good correlation between the donor number (DN) of the solvent and the /,max corresponding to the lowest energy of d-d transition [84], In spite of the small number of experiments, there is a certain relation between anion species and T.max, as shown in Table 3.10. 

Table 2, taken from Reichardt s review, describes representative approaches from the above three categories. Especially interesting are the parameter s donor number (DN), acceptor number (AN), and Er30, which appears in Table 3. 

Donor numbers of various solvents are listed in Table 3. The values range between 0 and about 60 kcal/mole. Polar solvents such as nitromethane are very weak donors. Solvents such as acetonitrile and propylenecarbonate are moderately strong donors. Ketone, ester, and ether solvents show medium donor properties. Amides and sulfones are strongly basic solvents with donor numbers 25 to 30, and aliphatic amines are very strong donors. 

Table 3 ETA) Values, Donor Numbers (DN), and Acceptor Numbers (AN) of Various Solvents... 

Table 8 compares oxidation potentials of selected solvents and their donor numbers [100], This table demonstrates that there is a correlation between higher donor numbers and lower stability limits for oxidation. A similar correlation for a larger variety of solvents presented by Zyat kova et al. [104] for LiAsF6 solutions is shown in Table 9. 

Table 8 Correlation between Donor Numbers and Oxidation Potentials for Selected Solvents... 

The high sensitivity of the g-values of low-spin iron(III) to structural variations and their large anisotropy imply that the prediction of the EPR spectra must be based on highly accurate structures12071. The MM-AOM method for low-spin iron(III) complexes was tested on a number of examples involving bi-, tri- and hexadentate ligands with amine and pyridyl donor sets (Table 10.8). 

Although there is some experimental evidence which points to a binding of iron ions by specific cytosolic proteins (see Cytosolic Iron Donor, below), these proteins, with the exception of transferrin, are available only in minute quantities, and the nature and extent of iron-protein interactions are poorly understood. Therefore, a number of nonprotein iron chelates have been studied as possible model donor complexes (Table I). Because of the high stability constants of, for example, the Fe(II)/Fe(III)-8-hydroxyquinoline and Fe(III)-ADP complexes (20), these iron-chelate complexes are unfavorable as iron donors, and in fact no energy-dependent uptake of iron has been detected using these complexes (21, 23). 

TABLE IV. Gutmann Donor Number (DN),(22c) Dielectric Constant ( EL)T(22a)... 

Unfortunately, donor numbers have been defined in the non-SI unit kcal mol b Marcus has presented a scale of dimensionless, normalized donor numbers DN, which are defined according to DN = DNl i%.% kcal mol ) [200]. The non-donor solvent 1,2-dichloroethane [DN = DN = 0.0) and the strong donor solvent hexamethyl-phosphoric triamide (EiMPT DN = 38.8 kcal mol DN = 1.0) have been used to define the scale. Although solvents with higher donicity than EiMPT are known [cf. Table 2-3), it is expedient to choose the solvent with the highest directly [i.e. calori-metrically) determined DN value so far as the second reference solvent [200] f The DN values are included in Table 2-3. 

Table 2-3. Donor numbers (donicities) DN [199, 200, 212, 241, 339] and normalized DN values [200] of a selection of thirty-six organic EPD solvents , determined calorimetrically in dilute 1,2-dichloroethane solutions at room temperature and valid for isolated EPD solvent molecules . ...

As the basic donor numbers were measured in an inert diluent, they reflect the donicity of the isolated EPD solvent molecules. In neat, associated EPD solvents an increase in the donicity should occur [199]. For such highly-structured solvents [e.g. water, alcohols, amines) the term bulk donicity has been introduced [201] in order to rationalize the deviations of these solvents in plots of Na NMR shifts [202] and ESR parameters ]203] vs. the donor numbers. Because of the great discrepancies which exist between the DAb ik values given in the literature, they are not included in this table. For a collection of bulk donicities, DAbuik. see reference [200], Table II. 

These quantities have been termed acceptor number AN (or acceptivity) and they were obtained from the relative P NMR chemical shift values corr (n-hexane as reference solvent) with respect to that of the 1 1 adduct EtsPO—SbCls dissolved in 1,2-dichloroethane, which has been arbitrarily taken to have the value of 100. The acceptor numbers are dimensionless numbers expressing the acceptor property of a given solvent relative to those of SbCb, which is also the reference compound for assessing the donor numbers. A compilation of organic solvents in order of increasing acceptor number is given in Table 2-5. 

Solvents can be classified as EPD or EPA according to their chemical constitution and reaction partners [65]. However, not all solvents come under this classification since e.g. aliphatic hydrocarbons possess neither EPD nor EPA properties. An EPD solvent preferably solvates electron-pair acceptor molecules or ions. The reverse is true for EPA solvents. In this respect, most solute/solvent interactions can be classified as generalized Lewis acid/base reactions. A dipolar solvent molecule will always have an electron-rich or basic site, and an electron-poor or acidic site. Gutmann introduced so-called donor numbers, DN, and acceptor numbers, AN, as quantitative measures of the donor and acceptor strengths [65] cf. Section 2.2.6 and Tables 2-3 and 2-4. Due to their coordinating ability, electron-pair donor and acceptor solvents are, in general, good ionizers cf. Section 2.6. 

The solvent-induced change in rate is, however, much larger than expected from the relatively small difference in polarity between nitromethane and hexamethylphos-phoric triamide. This, together with the correlation between rate decrease and increase in the solvent donor number DN cf. Table 2-3 in Section 2.2.6), suggests that specific solvation and stabilization of the diazonium ion by EPD solvents play a dominant role in the reaction (5-27). Very likely, formation of an EPD/EPA complex between the reactants in a rapid preequilibrium step precedes the rate-controlHng first step [504, 792],... 

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