Donor number application

The major disadvantage of the HSAB principle is its qualitative nature. Several models of acid-base reactions have been developed on a quantitative basis and have application to solvent extraction. Once such model uses donor numbers [8], which were proposed to correlate the effect of an adduct on an acidic solute with the basicity of the adduct (i.e., its ability to donate an electron pair to the acidic solute). The reference scale of donor numbers of the adduct bases is based on the enthalpy of reaction. A//, of the donor (designated as B) with SbCb when they are dissolved in 1,2-dichloroethane solvent. The donor numbers, designated DN, are a measure of the strength of the B—SbCb bond. It is further assumed that the order of DN values for the SbCb interaction remains constant for the interaction of the donor bases with all other solute acids. Thus, for any donor base B and any acceptor acid A, the enthalpy of reaction to form B A is ... 

Many physical chemists have embraced the concepts of donicity (donor numbers, DN) and acceptor numbers (AN) as developed by Gutmann and his co-workers [12], The DN is measured by the heat of reaction of the donor solvent and antimony pentachloride in a 1 1 ratio as a dilute solution in 1,2-dichloro-ethane. It is taken to be a measure of the strength of the Lewis base. The AN is measured as the relative shift of the 31P NMR peak in triethylphosphine oxide dissolved in the sample solvent. Hexane is given the value of zero on the scale, and antimony pentachloride is given the value of 100. The AN is taken to be a measure of the strength of the Lewis acid. The applications of the concepts have... 

Donor numbers are considered as semiquantitative measures of solute/EPD solvent interactions, and are particularly useful in the prediction of other EPD/EPA interactions in coordination chemistry. Numerous examples of the application of donor numbers have been given by Gutmann [26, 27, 30] cf. also [113, 133]. It has been shown that donor number correlations are parallel with correlations based on the highest occupied molecular orbital (HOMO) eigenvalues of EPD solvent molecules [139], For non-HBD solvents, a fair correlation has been obtained between their donor numbers and their gas-phase proton affinities FA, indicating that the DN values do indeed reflect the intrinsic molecular properties of EPD solvents [140]. 

This group of solvents is, however, limited in its applications. Other solvents, such as chloroform or benzene have been used for certain reactions involving covalent compounds. Thus triphenylchloromethane has been used as a source of chloride ions to combine with certain metal chlorides in solutions of acetic acid , nitroalkanes 5, chlorobenzenes and benzene. All of these reactions cannot be carried out in solvents of high donor numbers such as dimethyl sulphoxide or tributylphosphate . 

A large number of DTDAFs ( electron-rich olefins ) described above are very efficient donors, e.g., for their application in organic conductors however they are highly sensitive to air. Studies aimed at the preparation of such compounds, especially the aliphatic ones, have so far met with only limited success. For example, a few alkyl-substituted DTDAF derivatives could be detected electrochemically, but an attempt to isolate one of these only led to oxidation products (91JA985). Similarly, an elec-... 

However, EDTA has the widest general application in analysis because of its powerful complexing action and commercial availability. The spatial structure of its anion, which has six donor atoms, enables it to satisfy the coordination number of six frequently encountered among the metal ions and to form strainless five-membered rings on chelation. The resulting complexes have similar structures but differ from one another in the charge they carry. 

According to the theory of cyclic conjugation, the Hueckel rule is applicable only to a continuous cyclic conjugation, but not to a discontinuous one (Schemes 14 and 15). In the discontinuously conjugated molecules, electron donors and acceptors are alternately disposed along the cyclic chain [25].The thermodynamic stability depends neither on the number of n electrons nor the orbital phase properties, but on the number of neighboring donor-acceptor pairs. Chemical consequences of the continuity-discontinuity of cyclic conjugation are reviewed briefly here. 

The interaction of dihalogens, particularly diiodine, with sulfur and selenium electron donors has been an area of increasing interest over the past decade because of potential biological, pharmaceutical, and electronic materials applications [35,179]. Devillanova and coworkers have recently reviewed the solution behavior of a large number of chalcogenides and I2, particularly thiones, selones, sulfides, and selenides [180]. Correlations between computational methods, thermodynamic parameters, and spectroscopic data (UV/Vis, 13C NMR, Raman, UPS) were discussed. 

This work was partially supported by a grant from the Research Corporation and by the Donors of the Petroleum Research Fund administered by the American Chemical Society. Early work was supported by the National Institutes of Health (GM 30147), while instrumentation and theoretical development have been supported by the National Science Foundation. Much work described stems from the research of a number of postdoctoral and graduate student co-workers, whose names are noted in the cited references. Many of the samples for special applications came to us as gifts or via collaborations with researchers from around the world, most of whom are also coauthors in the publications. 

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