Acceptor number table

Comparing the donor and acceptor numbers (Table 3) for the solvents listed in Table 4 reveals that they should solvate the anions almost equally and the cations differently. This also enables one to assume that the associate does not contain a cation as such, but generally has the anion structure. Comparing the location of absorption peaks for solvated electron e and the associate shows that in all media the associate does not contain in its composition a solvated electron as such and the properties of the solvated electron e are more sensitive to the nature of the solvent than those of the associate. 

Table 1,5, Donor scales (Dg, DN and DNbulk) of some selected solvents, as well as acceptor number (AN) and hydrogen bond donor capacities (a).

The second important influence of the solvent on Lewis acid - Lewis base equilibria concerns the interactions with the Lewis base. Consequently the Lewis addity and, for hard Lewis bases, especially the hydrogen bond donor capacity of tire solvent are important parameters. The electron pair acceptor capacities, quantified by the acceptor number AN, together with the hydrogen bond donor addities. O, of some selected solvents are listed in Table 1.5. Water is among the solvents with the highest AN and, accordingly, interacts strongly witli Lewis bases. This seriously hampers die efficiency of Lewis-acid catalysis in water. 

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

There are numerous attempts to correlate solvent parameters with the reaction rate of Diels-Alder reactions122. Examples are the Brownstein Polarity Parameter S123, the Solvophobicity Parameter Sp124,125 the D-it parameter (based on the solvent effect on the reaction of tetracyanoethylene and diazodiphenylmethane with benzene as the reference solvent)126 or the Acceptor Number / /V127, l2X (a parameter which describes the ability of a solvent to act as an electron pair acceptor)129. These examples included either reactions that were next to insensitive to solvent effects (like that in Table 9) or reactions in which the reactants mainly interact with the electron pair on the donor atom of the solvent130. 

Fig. 7 Relationship between the reduction peak potential, Epc, of a-K6P2Wi8062 or a-K4SiWi2O40 versus the reduction peak potential, EpcFc+, of ferricinium and the acceptor number of studied solvents. Abbreviations are the same as in Tables 6 and 7. The solid line is the best linear regression fit to all the experimental points, including water as a solvent, (a) a-K6P2Wi8062 correlation coefficient for the solid line 0.974. The correlation coefficient for the best fit to nonaqueous solvents only is 0.994. (b) a-K4SiWi204o correlation coefficient for the solid line 0.983. The correlation coefficient for the best fit to nonaqueous solvents only is 0.995 (taken from Ref 34).

Table 3.8. Acceptor numbers and the Et scale for common solvents.

Functionally and mechanistically reminiscent of the pyruvate lyases, the 2-deoxy-D-ribose 5-phosphate (121) aldolase (RibA EC 4.1.2.4) [363] is involved in the deoxynucleotide metabolism where it catalyzes the addition of acetaldehyde (122) to D-glyceraldehyde 3-phosphate (12) via the transient formation of a lysine Schiff base intermediate (class I). Hence, it is a unique aldolase in that it uses two aldehydic substrates both as the aldol donor and acceptor components. RibA enzymes from several microbial and animal sources have been purified [363-365], and those from Lactobacillus plantarum and E. coli could be induced to crystallization [365-367]. In addition, the E. coli RibA has been cloned [368] and overexpressed. It has a usefully high specific activity [369] of 58 Umg-1 and high affinity for acetaldehyde as the natural aldol donor component (Km = 1.7 mM) [370]. The equilibrium constant for the formation of 121 of 2 x 10M does not strongly favor synthesis. Interestingly, the enzyme s relaxed acceptor specificity allows for substitution of both cosubstrates propional-dehyde 111, acetone 123, or fluoroacetone 124 can replace 122 as the donor [370,371], and a number of aldehydes up to a chain length of 4 non-hydrogen atoms are tolerated as the acceptor moiety (Table 6). 

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. 

Acceptor numbers of various solvents are also listed in Table 3. The values range from zero, for the reference solvent -hexane, to about 130, for trifluoro-methane sulfonic acid. For instance, the acceptor number of aliphatic alcohols varies between 27 and 41 (methanol). Within the group of dipolar aprotic solvents there are considerable differences in acceptor properties. Solvents such as propylenecarbonate, tetramethylene-sulfone, acetonitrile, dimethylsulfoxide, or nitromethane are stronger acceptors than solvents such as acetone, A-methylpyrroli-done, or dimethylacetamide. The acceptor strengths of amine solvents vary considerably with the degree of substitution. For instance, triethylamine has no acceptor properties. 

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

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. 

Acceptor numbers are less than 10 for nonpolar non-HBD solvents, they vary between about 10... 20 for dipolar non-HBD solvents, and they cover a wide range of about 25... 105 for protic solvents cf. Table 2-5). Surprisingly, benzene and tetra-chloromethane have stronger electrophilic properties than diethyl ether and tetrahy-drofuran. Acceptor numbers are also known for binary solvent mixtures [70, 213]. 

Table 2-5. Acceptor numbers (acceptivities) AN [70, 213, 339] of forty-eight organic EPA solvents, determined P-NMR spectroscopically at 25 °C.

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 excellent Z/ t(30) correlation for a selected set of 15 solvents common to both scales has been used to calculate t(30) values from Z values for acidic solvents for which t(30) values are not available [172] cf. footnote of Table 7-3. A similar satisfactory linear correlation between t(30) values and acceptor numbers allows the calculation of AN values that are not directly available [207, 294b]. 

Fig. 2. The change in the formal potential of the phenazine/phenazine radical anion system (against the Foe/Foe electrode) with the acceptor number of the solvent [91], Abbreviations are defined in Table 1.

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... 

Values of A estimated using the data for Cl ion given in table 4.7 are plotted against the Gutmarm acceptor number in fig. 4.18. A very good linear correlation with a correlation coefficient of 0.978 is obtained. The relationship between A and AN is... 

Fig. 7.7 Plot of the logarithm of the rate constant for reaction (7.3.23) in various solvents against the solvent s acceptor number AN (table 4.10).

Table 3 contains the physical properties of solvents that are used for dissolving alkali metals. Besides boiling point (b.p.) and viscosity (the data enable one to judge on the experimental potentialities inherent in a solvent) the Table contains values of dielectric constant and of donor and acceptor numbers (DN, AN). It is hard to notice any correlation between the macroscopic properties of the solvents, on the one hand, and their ability to dissolve alkali metals and the possibility of electrochemical generation of solvated electrons, on the other hand. 

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. 

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