Solvent correction

The explicit definition of water molecules seems to be the best way to represent the bulk properties of the solvent correctly. If only a thin layer of explicitly defined solvent molecules is used (due to hmited computational resources), difficulties may rise to reproduce the bulk behavior of water, especially near the border with the vacuum. Even with the definition of a full solvent environment the results depend on the model used for this purpose. In the relative simple case of TIP3P and SPC, which are widely and successfully used, the atoms of the water molecule have fixed charges and fixed relative orientation. Even without internal motions and the charge polarization ability, TIP3P reproduces the bulk properties of water quite well. For a further discussion of other available solvent models, readers are referred to Chapter VII, Section 1.3.2 of the Handbook. Unfortunately, the more sophisticated the water models are (to reproduce the physical properties and thermodynamics of this outstanding solvent correctly), the more impractical they are for being used within molecular dynamics simulations. 

Table 7.9 Electronic Absorption Bands for Representative Chromophores Table 7.10 Ultraviolet Cutoffs of Spectrograde Solvents Table 7.11 Absorption Wavelength of Dienes Table 7.12 Absorption Wavelength of Enones and Dienones Table 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy Table 7.14 Primary Bands of Substituted Benzene and Heteroaromatics Table 7.15 Wavelength Calculation of the Principal Band of Substituted Benzene Derivatives...

Sets of empirical rules, often referred to as Woodward s rules or the Woodward-Fieser rules, enable the absorption maxima of dienes (Table 7.11) and enones and dienones (Table 7.12) to be predicted. To the respective base values (absorption wavelength of parent compound) are added the increments for the structural features or substituent groups present. When necessary, a solvent correction is also applied (Table 7.13). 

TABLE 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy... 

Second-order rate coefficients at 20 °C were as follows benzene (0.0133), toluene (1.26), p-xylene (62) o-xylene (70.2), and i-propylbenzene (0.395). It is difficult to evaluable the quantitative significance of this data, however, since there must be a solvent correction factor to each rate, arising from the differing polarities of the media. That this can be significant can be seen from the data in Table 67,... 

The relative bond enthalpies from the photoacoustic calorimetry studies can be placed on an absolute scale by assuming that the value for D//(Et3Si—H) is similar to D/f(Me3Si—H). In Table 2.2 we have converted the D/frei values to absolute T>H values (third column). On the basis of thermodynamic data, an approximate value of D//(Me3SiSiMc2—H) = 378 kJ/mol can be calculated that it is identical to that in Table 2.2 [1]. A recent advancement of photoacoustic calorimetry provides the solvent correction factor for a particular solvent and allows the revision of bond dissociation enthalpies and conversion to an absolute scale, by taking into consideration reaction volume effects and heat of solvation [8]. In the last colunm of Table 2.2 these values are reported and it is gratifying to see the similarities of the two sets of data. 

Revised values taking into consideration solvent correction factors [8]. 

EQUILIBRIUM WITH SOLVENT CORRECTION IVIN etol (1965)... 

TABLE 5. Calculated [B3LYP/6-311+G(d,p)] activation parameters (kcal mol and eu) for the epoxidation of cyclohexene and isobutene with dimethyldioxirane (DMDO), peroxybenzoic add (PBA), m-chloroperoxybenzoic add (m-CPBA) and peroxyformic acid (PFA). Solvent corrections were performed with the COSMO model. The numbers in bold are experimental values -Numbers in parentheses are at the B3LYP/6-311- -G(3df,2p)//B3LYP/6-311- -G(d,p) level of theory... 

Figure 6-14 Solvent-Corrected 6-311+G vs. Experimental Aqueous-Phase Relative Acidities of Carboxylic Acids... 

Figure 6-17 Solvent-Corrected 6-31G vs. Experimental Aqueous-Phase Relative Basicities of Amines...

A value for the equivalent conductance at infinite dilution for lithium bromide in acetone was first calculated in 1905 by Dutoit and Levier (13) for 18°C 166 12 1 cm2 eq-1. A graphical method involving Ostwald s dilution law (A-1 = Ao-1 + cA/KdAq2), applied to their data in 1913 by Kraus and Bray (14), produced values of 5.7 X 10 4 for Kd and 165 12 1 cm2 eq-1 for Aq. Deviations from the mass action law (nonlinearity in the graph) become appreciable at concentrations of ca. 10 3N. Both groups pointed out that measurements in acetone are liable to error from several sources, including the presence of solvent impurities and exposure to light. A solvent correction of 21% was applied to their most dilute solution. 

In 1939 Dippy, Jenkins, and Page (16) found that the phoreogram for lithium bromide in acetone at 25 °C contains an inflection point, and they were unable to get A0 by extrapolation. Inspection of their phoreogram indicates, however, that A0 is nearer Serkov s value than that of Kraus and Bray. They noted that although different batches of acetone had different specific conductances, the data points of the phoreogram lay uniformly on a smooth curve. This they considered evidence of the adequacy of the solvent correction employed. 

Series V consisted of runs in which lithium bromide was added to a fixed amount of dimethyl bromosuccinate in acetone. Table I shows that the solvent correction is greater than for Series I, but less than for Series II—IV. The specific conductance of lithium bromide in dimethyl bromosuccinate-acetone is only slightly less than in acetone. This is in contrast to Series II—IV. Table II shows that both Ao and K are less than for Series I but greater than for Series II—IV. Table I indicates that for Series V the trends in each column are the same as for Series I. The results of Series V are in agreement with those of Bjornson and those of Olson and Cunningham. 

Values obtained by using volume and solvent correction factors (see L. G. Longsworth and D. A. MacInnes Chem. Rev. 11, 171 (1932)). ... 

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