Calculations anion reactions

In this paper the electtode anodic reactions of a number of dihydropyridine (DHP) derivatives, quantum-chemical calculations of reactions between DHP cation-radicals and electrochemiluminescers anion-radicals (aromatic compounds) and DHP indirect ECL assay were investigated. The actuality of this work and its analytical value follow from the fact that objects of investigation - DHP derivatives - have pronounced importance due to its phaiTnacology properties as high effective hypertensive medical product. 

This view is been confirmed by an electrochemical product study (Hatta et al. 2001) that is discussed below. The pfCa value of the Thy radical cation has been determined at 3.2 (Geimer and Beckert 1998). When the position at N( ) is substituted by a methyl group and deprotonation of the radical cation can no longer occur at this position, deprotonation occurs at N(3) (Geimer and Beckert 1999 for spin density calculations using density functional theory (DFT) see Naumov et al. 2000). This N(3) type radical is also produced upon biphotonic photoionization of N(l)-substituted Thy anions [reaction (7)] in basic 8 molar NaC104 D20 glasses which allowed to measure their EPR spectra under such conditions (Sevilla 1976). 

Standard basis sets are not suitable for calculating anions. The reason is that the exponents tf (which give the size of AOs) are optimized for neutral molecules. With these exponents, the electrons of anions are still compelled to move in the same volumes, so their repulsion is unduly exaggerated. A small basis set is not flexible enough to alleviate this effect. In particular, the 3-21G basis set gives unreliable activation energies and geometries for ionic reactions. Take a gas-phase SN2 reaction. It is... 

For the first decomposition step the formation of [Bi2Hi2] anion as a possible intermediate phase is discussed [35]. Different enthalpy values in the range —40 to 5 7 kj mol H2 for the first decomposition step at about 277 ° C have been determined from experimental data [35, 36[. From density functional theory (DFT) calculations a reaction enthalpy of 38 kj mol H2 at 27 ° C was confirmed [37]. Cycling experiments performed at 350 ° C under 10 MPa hydrogen lead to re-absorption of more than 3 wt.% hydrogen, showing lhat the second decomposition step is reversible [33, 36]. 

This shift was interpreted with the aid of DFT calculations in terms of molecular conformational changes of (NpS.. SNp)" radical anion due to the elongation of the S-S bond from 0.213 nm in a rigid matrix at 77 K up to 0.290 nm in fluid phase at 273 K. The (NpS.. SNp)" radical anion dissociates into napthylthiyl radical and thionaphtholate anion [reaction (38)] in DMF solution at 293 K with a first-order rate constant k= 10 s"h... 

Notice the diversity in structure of lhe.se proton dunurs. They include the classical hydrochloric acid (reaction a). Ihc weakly acidic dihydrogen phosphate anion (reaction b). the ammonium cation as is found in ammonium chloride (reaction c), the carboxylic acetic acid (reaction d). Ihc cnolic form of phenobarbital (reaction e), Ihe carboxylic acid moiety of indomelhacin (reaction j), Ihc imidc of saccharin (reaction g). and the prolonaied amine of ephedrine (reaction h). Because all are proton donors, they mu.st be treated as acids when calculating the pH uf a solution or percent ionization of the drug. At the same lime, as nuted below, there are important differences in the pharmaceutical properties of ephedrine hydrochloride (an acid salt of an amine) and lho.se of indomelhacin. phenobarbital. or saccharin. 

Various thermodynamic cycles are used in pKa calculations. Although previously a source of confusion in the field, it is now clear that as long as the most accurate experimental values are used, and no explicit water molecules are added, the choice of cycle should just be a matter of convenience. The most common is based on Eq. (1) and is diagramed in Figure 1, where a molecule is simply deproto-nated, yielding a corresponding base and the proton in solution [1,2,4]. This cycle depends on the accuracy of the continuum model used to determine the anion (reaction 1) or cation (reaction 8) solvation energies, calculations that vary in... 

Nonempirical calculations of reaction complexes formed during anionic polymerization ofbutadiene, in the presence of stilbenes, have been made [87]. The mechanism of cis-trans isomerization in the terminal unit of the living polymer consisted in concerted rotation about the Cp bond, and the migration of Li between and Cy... 

Armed with this bit of thermodynamics, we can now calculate the free energy of adsorption of an anion, reaction 5 as ... 

By analysis of the data of the dependence of signal on time during electrolysis it is possible by means of equations for homogeneous chemical kinetics to calculate the reaction order, the reaction rate constant, and the half-life for the primary process involved in cleavage of the radical ions [76]. It is thus possible to determine kinetic parameters for the second-order cleavage of radical anions with half-lives not shorter than 1 sec at an initial concentration of Co = 540 mole/liter. 

The transition-state spectroscopy experiment based on negative-ion photodetachment described above is well suited to the study of the F + FI2 reaction. The experiment is carried out tln-ough measurement of the photoelectron spectrum of the anion FH,. This species is calculated to be stable with a binding energy of... 

The effect of micelles of SDS, CTAB and C12E7 on the apparent second-order rate constants of the Diels-Alder reaction between nonionic 5.1a, anionic 5.1 f and cationic 5.1g with 5.2 is reported in Table 5.1. These apparent rate constants are calculated from the observed pseudo-first-order rate constants by dividing the latter by the overall concentration of 5.2. 

The reaction between a trinuclear metal carbonyl cluster and trimetbyl amine borane has been investigated (41) and here the cluster anion functions as a Lewis base toward the boron atom, forming a B—O covalent bond (see Carbonyls). Molecular orbital calculations, supported by stmctural characterization, show that coordination of the amine borane causes small changes in the trinuclear framework. 

Is para-nitrofluorobenzene more or less susceptible to attack by methoxide than fluorobenzene Calculate the energetics of the reaction. (Energies for phenyl fluoride and para-nitrofluorobenzene methoxide anion adducts are available.)... 

Substituted pyrazolin-5-ones have only three and -substituted pyrazolin-3-ones only two tautomers, since now the corresponding 19c and 19d structures are isomers. The calculations involved l-methylpyrazolin-5-one (PM3/6-3H-G, anions and cations), l-phenyl-3-methyl-2-pyrazolin-5-one (DFT, radical reactions) [97JPC(A)3769], and l-(2, 4 -dinitrophenyl)-3-methyl-2-pyrazolin-5-one [B3LYP/6-31G and the crystal structure (Section V,D,2)] (98NJC1421). 

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