Solvent chemical donor number

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. 

An important chemical measure of solvent polarity is the donor number, DN. It is a measure of the Lewis base donor power of the solvent. DN is defined as the negative enthalpy for the reaction of the solvent with the standard Lewis acid SbCls (eqn. 3.8). The enthalpy measurements are carried out in an inert solvent, 1,2-dichloroethane, which has a donor number of zero. The units are kcal/mol. 

Tab. 1.5 Chemical properties of organic solvents of electrochemical interest. Donor numbers (DN), accepptor numbers (AN), and autoprotolysis constants (p/[Pg.18]

FIGURE 3. 29Si chemical shifts of trimethylsilanol vs. solvent donor numbers, DN. Reproduced by permission of The Chemical Society of Japan from Reference 44... 

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. 

Dichloroethane is obviously not a chemically inert solvent under all circumstances. For example, the EPD solvent triethylamine is rapidly quatemized by 1,2-dichloroethane under the catalytic action of SbCb, leading to an overestimated donor number for triethylamine [128]. Even solutions of HMPT and SbCb in 1,2-dichloroethane contain non-negligible amounts of charged species, the formation of which contributes to the measured enthalpy [138]. 

Structured neat EPD solvents [e.g. water, alcohols, amines) the term bulk donicity has been introduced [135] in order to rationalize the deviations of these solvents in plots of 23Na NMR chemical shifts [136] and ESR parameters [137] vs. the donor number. Unfortunately, great discrepancies exist between the DiVbuik values given in the Hterature when estimated by different methods. For this reason, they are not included in Table 2-3 in Section 2.2.6 see reference [133] for a collection and discussion of bulk donicities, f iVbulk-... 

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... 

In the sections that follow, the basic theory of these techniques will be discussed only insofar as it is specially relevant to organotin compounds. It must always be borne in mind that the structures of organotin compounds which carry functional groups may be dependent on the physical state (gaseous, solid, or liquid), and, when the compounds are in solution, on the nature of the solvent and on the concentration. For example, the Sn-Cl stretching frequency in the far IR spectra of trimethyltin chloride in solution can be correlated with the donor number of the solvent. Caution must therefore always be exercised in attempting to quote typical values for properties such as vibrational frequences or NMR chemical shifts. 

Polar molecular solutes have been used to probe the donor-acceptor properties of polar solvents. chemical shifts have been measured for interaction between trifluoroiodomethane and the solvent molecule as electron pair donor [24]. As interaction between the donor molecule and the iodine atom in this molecule increases, electron density at the fluorine atoms increases with a resulting positive chemical shift in the NMR signal. An excellent correlation between these shifts and the Gutmann donor number was reported [24]. 

A 1H NMR study (6 ) found that the chemical shifts of the N-H protons were very sensitive to solvent with the shifts being related to the donor number (j) of the solvent, i.e. the ability of the solvent to donate electrons to form a hydrogen bond with the N-H protons. Further, the N-H protons that were essentially equatorial in the puckered five-membered chelate ring showed larger variations in their 6 values than the axial protons. The differences in the 6 values for the equatorial and axial protons for the NH2 groups were in the order ... 

The chemical shifts have been correlated satisfactorily with the solvent parameters AN (acceptor number (ref. 28)), DN (donor number (ref. 29)) and e (dielectric constant) for a set of nine solvents (acetone, acetonitrile, DMF, DMAc, nitrobenzene, sulfolane, HMPT, benzonitrile, methanol) (ref. 17) (Fig. 4). The predominant weight of AN indicates clearly the basic character of solvated fluorides which, however, is strongly modulated by HF-solvation and can be quantified in that way. Thus, the correlation between the chemical shift and the reactivity of soluble fluoride anions could, in principle, allow to predict their fluorination efficiency in any solvent. 

Various attempts have been made to classify solvents, e.g. according to bulk and molecular properties empirical solvent parameter scales hydrogen-bonding ability and miscibility >. In table I solvents are divided into classes on the basis of their acid-base properties which can be used as a general chemical measure of their ability to interact with other species. Detailed information on these and other solvents, their symbols, fusion and boiling pointe and Gg), bulk properties (6,Ti, q), and currently-used correlation parameters DN (donor number), Ej-value, and AN (acceptor number) is given in Appendix A-1. 

Popov s comprehensive multinuclear NMR studies of alkali ions in non-aqueous solvents 304,3< -3i6) encompassing concentration-depfcndence of chemical shifts, ion-pair formation, influence of the solvent and correlation with donor numbers, and the role of macrocyclic polyethers and cryptands, are evidence of the powerful tool provided by NMR methods for the investigation of non-aqueous electrolyte solutions. 

In considering the solvent effects on the static aspects of structure and properties, the effects due to the presence of the other ions and solute molecules cannot be neglected. For exanple, the 2 Na chemical NMR-shifts of sodium tetraphenylborate of the same concentration in different solvents are linearly related to the donor number of the solvent the greater the solvent-solute interaction, the more is the net positive charge at the sodium ion decreased. However, for sodium iodide no such relationship is found, because the stronger donor properties of the iodide ion as compared... 

NMR spectroscopy has been used to characterize aluminium chromium mixed oxides.The Mo chemical shifts, electronic absorption bands, and solvent donor numbers have been examined for [Mo2(02CR)4L2] solvent adducts. NMR spectroscopy has been used to confirm the presence of three different types of oxygen atoms in [ (ri -4-MeC6H4Pr )Ru 4Mo40i6]. The NMR spectrum of [HPW9034] is a five line, 1 2 2 2 2, spectrum. has... 

Erlich and Popov (64) have reported a very useful correlation of Na" chemical shifts with the Gutmann donor number of solvents. As the solvent becomes a better electron donor, the resonance moves downfield. The regression is quite good, especially if one removes from it the point for water, a legitimate deletion since this point corresponds to octahedral as compared with tetrahedral coordination in all the others. Likewise, with... 

Table 16. Potassium--39 Infinite Dilution Chemical Shifts for K " and Donor Numbers of the Corresponding Solvents...

Sodium tetrapheiiylborate, NaC104, Nal and NaCNS in a number of nonaqueous solvents Chemical shifts for Na studied as a function of concentration results discussed in terms of contact ion pairs and electron donor abilities of solvents 97... 

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