Gutmann numbers, correlations

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]. 

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. 

To start with gas-phase data, ionization potentials (IP) and the derived heats of formation of radical cations are available for a large number of organic species (Franklin et al., 1969 Gutmann and Lyons, 1967 Turner, 1966), whereas electron affinities (EA) are far more scarce (for a recent review, see Janousek and Brauman, 1979). For both types of data one has to estimate heats of solvation for participating species in order to obtain E° in solution, and this is known to be an uncertain procedure (Mortimer, 1962). An alternative is to use the rather good correlations that are available between gas phase and solution data for estimating unknown solution values (see below). 

This 5phOH scale was further extended by Makitra et al. [242]. It has been shown that the spectroscopically determined 5phOH values correlate well with Gutmann s calori-metrically measured donor numbers DN [243] cf. Eq. (7-10). 

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... 

Various criteria have been followed in an attempt to establi quantitative scales of acidity and basicity. In order to account for solvation and ionic dissociation phenomena Gutmarm introduced a parameter called donor number, DN, which correlates the behaviour of a donor sdvent towards a given solute with respect to the coordinating ability of a reference solvent towards the same sdute. The basicity of a solvent can be related to the enthalpy of its reaction with a reference acid. Gutmann s DN scale is built on the equation... 

TTie solution phase ionization potentials of Br in 16 solvents have been determined by photoeiectron emission spectroscopic technique. The values obtained as the threshold energy E for Br" in various solvents are found to be correlated well with the Mayer-Gutmann acceptor number of solvent. The reorganization energy AC, of solvent after the photoionization of Br" has been obtained from the E value. The AG, values are well reproduced by using a simple model which incorporates the dipole-dipole repulsion and the hydrogen-bond formation in the first solvation layer. The solvation structures of Br" determined by EXAFS are used for the AG, calculation. 

The PEE spectra were obtained with the apparatus in this laboratory. The , values measured with 16 solvents are summarized in Table 1. It is found that the E, value correlates with the Mayer-Gutmann acceptor number. 4, . This correlation indicates that the electronic energy states of solvated anions are mainly... 

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. 

It has been tried to overcome this drawback by the use of multi-parameter correlation equations. One approach involves the Gutmann donor number (DN) [81]. By this the absorption maximum (v ) observed for a dye in a certain liquid can be calculated from the absorption maximum of the dye in a reference medium (Vmax.o) according to [82-85]... 

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]. 

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