INDEX anion ordering

A theoretical study at a HF/3-21G level of stationary structures in view of modeling the kinetic and thermodynamic controls by solvent effects was carried out by Andres and coworkers [294], The reaction mechanism for the addition of azide anion to methyl 2,3-dideaoxy-2,3-epimino-oeL-eiythrofuranoside, methyl 2,3-anhydro-a-L-ciythrofuranoside and methyl 2,3-anhydro-P-L-eiythrofuranoside were investigated. The reaction mechanism presents alternative pathways (with two saddle points of index 1) which act in a kinetically competitive way. The results indicate that the inclusion of solvent effects changes the order of stability of products and saddle points. From the structural point of view, the solvent affects the energy of the saddles but not their geometric parameters. Other stationary points geometries are also stable. 

A theoretical evaluation of the aromaticity of the pyrones pyromeconic acid, maltol, and ethylmaltol along with their anions and cations was carried out at several levels (Hartree-Fock, SVWN, B3LYP, and B1LYP) using the 6-311++G(d,p) basis set <2005JP0250>. The relative aromaticity of these compounds was evaluated by harmonic oscillator model of aromaticity (HOMA), nucleus-independent chemical shifts (NICSs), and /6 indexes and decreases in the order cation > neutral molecule > anion. 

In this work, we discuss the results of DFT calculations for some all-metal clusters with the general formula MAI/ at a validated level of theory and numerical precision and compute a number of accepted properties to describe aromaticity, such as 17, geometrical parameters, the DI, and the NICS indexes. Hereby, we pursue the evaluation of DFT calculations and reactivity descriptors to explain and assess aromaticity in the anionic all-metal clusters derived from the Al/- unit. We determine the effect of different charges and multiplicities on the geometry of Al/(n = —2, —1,0,1) and calculate the structures of new complexes MA14" where M = (Li+, Na+, K+), (Be+2, Mg+2, Ca+2), (Sc+3, Ti+4), and (B+3, Al+3, Ga+3). In order to compare the DFT reactivity descriptors, we compute other parameters (NICS and DIs) and study periodic trends. 

It is also very important to monitor the effects of the upper potential limit since the potential at which oxygen reduction begins implies hydroxide or oxide co-formation on platinum. There are many studies of the reaction on the three low-index platinum surfaces [95,98]. The catalytic activity of these surfaces decreases in the order of Pt(l 10) > Pt(l 11) > Pt(100) in perchloric acid solution [96], while the order is Pt(110) > Pt(100) > Pt(l 11) in sulfuric acid solution [93]. In the case of Pt(lll), the formation of a two-dimensional ordered ad-layer of specifically adsorbed (bi) sulfate anions is the main reason for the inhibition of oxygen reduction. Moreover, the direct four-electron mechanism was found for the three surfaces in acidic media, while the reaction mechanism varied to a two-electron reduction on the Pt(lll) and Pt(100) due to the shielding of the hydrogen adatoms. 

High-temperature ionic solvents are known to contain relatively high total concentrations of cations (e.g. in the KCl-LiCl eutectic, the concentration of Li+ is approximately equal to 8.5 mol kg-1 of the melt). Usually, cation-anion complexes in molten salts are characterized by co-ordination numbers of the order of 4-6. This means that the maximal consumption of acidic cations does not exceed 0.4-0.6 mol kg-1 in diluted solutions with concentrations close to 0.1 mol kg-1. This estimate is considerably lesser than the initial concentration of acidic cations in the pure melt. In the case of the KCl-LiCl eutectic melt, this consumption is only of the order of 5-7%, and the value of NMe+ in equation (1.3.16) may be assumed to be constant. Therefore, for each ionic solvent of the second kind (kind II) the denominator in equation (1.3.16) is a constant which characterizes its acidic properties. We shall define p/L = -log /L to be the relative measure of acidic properties of a solvent and call it the oxobasicity index of ionic melt [37, 162, 181]. Since the direct determination of the absolute concentration of free oxide ions in molten salts is practically impossible, the reference melt should be chosen— for this melt, /L is assumed to be 1 and p/L = 0. The equimolar KCl-NaCl... 

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