Bulk Solvent Effects

The bulk solvent effect on the reaction energy, described by the lower portion of Scheme 2.3, significantly modifies the relative importance of the uncatalyzed and water-assisted alkylation mechanism by o-QM in comparison to the gas phase. 

The redox potentials found for given concentrations of acids are related to the Ka values, which are indicative of their EPA properties. The effects become more pronounced at extremely high acid contents and increase from propionic acid to formic add. This is a bulk solvent effect (formic acid is more highly structured than propionic acid). 

The fact that these reactions are indeed a plausible approach to interconnect gas-phase and solution reactivity has been contested by Henchman el al. (1983). The basis for their argument is that for n = 1, reaction (30) yields Br -I- H20 + CH3OH as products, and not the solvated anion. Thus, they conclude that bulk solvent effects cannot be properly extrapolated from the data of reaction (30). While the rigorous argument is correct, the rate constant trend is very useful to show that successive solvation of the reagent anion will slow down the reaction even on a thermochemical basis. 

Isomer stabilities and activation energies have been calculated for keto-enol tautomerization of simple carbonyl compounds, MeC(R)=X (X = O R = H, Me) 129 both specific and bulk solvent effects have been analysed. Related isomerizations of acid derivatives (R = F, CN) and other related structures (R = H X = CF12, NH, S) are compared. 

The water-promoted hydrolyses of a bicyclic amide, l-azabicyclo[2.2.2]octan-2-one (87), and a planar analogue, l,4-dimethylpiperidin-2-one (88), were studied using density functional theory in conjunction with a continuum dielectric method to introduce bulk solvent effects. The aim of these studies was to reveal how the twisting of the C-N bond affects the neutral hydrolysis of amides. The results predict important rate accelerations of the neutral hydrolysis of amides when the C-N bond is highly twisted, the corresponding barrier relaxation depending on the specific reaction pathway and transition state involved.85... 

Thereby, it was also found that bulk solvent effects need to be included in the computations as well, and that the simultaneous application of both a continuum solvent model (conductor-like scrrening model [127,128]) and an... 

At 638 nm in cyclohexane, the wavelength of maximum absorbance of the bis(naphtho[l,8-A ]thiopyranone) 628 is 98 nm to the red of thioindigo (Amax 540 nm). These values are in close agreement with those predicted by a TD-PBE0/6-311+G(2, />)//PBE0/6-311G6f,/>) approach that allowed for bulk solvent effects by means of a polarizable continuum model <2006JA2072>. 

In the present paper the thermodynamic and kinetic aspects of the proton transfer reactions among cytosine tautomers assisted by specific solvent molecules was theoretically investigated. For the time being, bulk solvent effects were not considered and attention was only focused on the influence of hydrogen bonding on both (i) tautomers relative stability and (ii) the catalytic process occurring between adjacent positions of cytosine. The computational results on point (i) are compared with those of PCM calculations [15]. The results on point (ii) are discussed with reference to the conclusions of other theoretical studies available in the literature [16,17]. 

On the basis of the present calculations on simplified hydrated models we can safely suggest that cytosine tautomerization reactions should take place at room temperature, and that the Cl Cl conversion is kinetically unfavoured by 2-4 kcal mof with respect to the Cl C3 and C4 C5 processes. Bulk solvent effects, which are not included in the present study, are expected to provide only a fine tuning of the activation energies, as variations of the dipole moment from minima to transition states are generally less than 1 Debye (Table 2). 

In fact, SHELXL is not necessarily right when it suggests the performance of an extinction correction. Other effects can mimic extinction and SHELXL cannot easily distinguish between certain bulk solvent effects and extinction. 

Tiwari, S.,Mishra,P. C., Suhai, S. (2008). Solvent effect of aqueous media on properties of glycine significance of specific and bulk solvent effects, and geometry optimization in aqueous media. Int. J. Quantum Chem. 108,1004—1016. 

It is clear from our results that bulk solvent effects control to some extent the reactivity of Co(II)-N4 species, even in absence of any specific solute-solvent interactions. Work is in progress in order to obtain even more reliable results, aiming to investigate the role of the first solvation shell in the electro-oxidation... 

Because the importance of local density enhancement effects depends upon the compressibility of the fluid, these effects have an unusual bulk density (pressure) dependence. Below the critical density [65] the local density enhancement effects increase with increasing bulk-density, whereas at densities greater than the critical density, these effects will decrease with further increases in the bulk-density. This is in contrast to the bulk solvent effects, which increase monatonically with increasing bulk-density as the solvent properties, e. g. the dielectric constant, vary from their gas-like to liquid-like values. Hence, the bulk-density dependences of the activation barriers, AG(T5), on... 

The cluster-continuum moder iUuslrated in scheme 1 was used to simulate the most common electrolytes of LIBs. The supra-molecular cluster applied to the inner ring (scheme 1) incorporates the mutual effect between salt and solvent molecules by including the first solvation shell of the salt. Due to the minor effect that the salt anion XT has on the reductive behavior of solvent molecules coordinated with Li, XT and the surrounding solvent molecules are not discussed in the current chapter. The bulk solvent effect in the second ring of scheme 1 is treated by polarized continuum models, such as PCM, conductor-like PCM (CPCM), isodensity PCM (IPCM), and self-consistent isodensity PCM (SCl-PCM), which were developed on the basis of the Onsager reaction field theory and are recognized to provide reliable results for systems without specific interactions such as hydrogen bond. 

For small clusters of only one solvent molecule, Li (S) (S=EC, PC and VC), both the inner and the bulk solvent effect are fully optimized with density functional theory, using the B3PW91 method and the 6-31 l-i-HG(d,p) basis set, while the bulk solvent effect is accounted for using the CPCM method. The overall procedure is denoted as CPCM-B3PW91/6-311-H-HG(d,p). For the cases with more than one solvent molecules in the cluster models, B3PW91 with the basis set 6-31G(d) is employed to optimize the structure of Li (S) (n > 1) and... 

Taking into account the bulk solvent effect with the CPCM-cluster model, the reduction potentials are further estimated for the following two red-ox reactions in which VC and EC/PC are reduced, respectively ... 

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