Organic based reducing agents. Prediction of oxidation potentials of Election rich radicals from the Analysis of AM1 charge density Distributions [1]

Electrochemical oxidation potentials ofmethoxy substituted benzyl, l-naphthylmethyl, phenethyl, diphenylmethyl and cumyl radicals, substituted at the α-, 2-, 3-, or 4-position have been measured by photomodulation voltammetry. These data are compared to ionization potentials calculated using the AM1 molecular orbital method. Although a plot of the oxidation potentials versus the AM1 ionization potentials is quite scattered, an essentially linear relationship is found for a plot of the relative oxidation potential (i.e. compared to that of the unsubstituted parent radical) and the fraction of charge in the 2p_z orbital of the parent cation. The relationship is remarkable considering the potentials span a range of ca. 1 eV (23 kcal mol ^-1) and the fractional charges span a range of ca. 0.5 of a unit charge. The utility of such a relationship as a predictive tool in the design of simple organic based reducing agents is discussed.     

A theoretical photoelectron spectrum of cyanogen by a Green-function method

A Green-function method is used to calculate a photoelectron spectrum of C₂N₂ including the vibrational structure. The calculated spectrum and the experimental spectrum are in good agreement. It is found that the second band is due to ionization of the 5a_g electron. In addition predictions are made concerning the ionization potentials and vibrational structure of low lying bands which have not yet been measured. The ionization potentials obtained in the different orders of the perturbation expansion of the self-energy part are discussed as well as the influence of many-body effects on the vibrational coupling constants.     

The calculation of ionization energies by perturbation,configuration interaction and approximate coupled pair techniques and comparisons with green's function methods for Ne,H2O and N2

The vertical valence ionization potentials of Ne, H₂O and N₂ have been calculated by Rayleigh-Schrödinger perturbation and configuration interaction methods. The calculations were carried out in the space of a single determinant reference state and its single and double excitations, using both the N and N - 1 electron Hartree-Fock orbitals as hole/particle bases. The perturbation series for the ion state were generally found to converge fairly slowly in the N electron Hartree-Fock (frozen) orbital basis, but considerably faster in the appropriate N - 1 electron RHF (relaxed) orbital basis. In certain cases, however, due to near-degeneracy effects, partial, and even complete, breakdown of the (non-degenerate) perturbation treatment was observed. The effects of higher excitations on the ionization potentials were estimated by the approximate coupled pair techniques CPA′ and CPA″ as well as by a Davidson type correction formula. The final, fully converged CPA″ results are generally in good agreement with those from PNO-CEPA and Green's function calculations as well as experiment.     

Ionization energies of cesium and cesium oxide clusters

The vertical ionization potentials of 7 cesium and 86 oxidized cesium clusters were determined using the technique of photoionization mass spectrometry. The spectra were obtained using a tunablecw dye laser for clusters in a mass range 1 to 2024 amu. The vertical ionization potentials (IP) are presented as a function of size and composition. The ionization energies of cesium clusters, Cs_n, decrease with cluster size. Unusually low IP were observed for the enneamer, Cs₉, and for the cesium monoxide Cs₁₁ O. With increasing oxidation of the cesium metal clusters the IP decreases (suboxides) reaches a minimum at Cs(Cs₂O)_n and then increases (superoxides).     

Laser photoionization and spectroscopy of gas phase silver clusters

Silver clusters containing up to 40–50 atoms are produced by laser vaporization in a pulsed-nozzle molecular beam source and studied with laser photoionization mass spectroscopy. A variety of Nd:YAG pumped dye laser and UV excimer laser wavelengths are used to achieve ionization. Ionization dynamics are studied by varying the laser wavelength and fluence. Bracketing experiments under single-photon ionization conditions are used to estimate ionization potentials as a function of cluster size. An even-odd ionization potential alternation is observed with odd-numbered clusters (N=3, 5, 7 ...) having lower ionization potentials than adjacent even-numbered species. Shell closings at clusters containing 2, 8 20 and 40 electrons are observed consistent with a one-electron shell model picture of cluster electronic structure. Resonance-enhanced ionization produces a vibrationally resolved spectrum for the trimer, Ag₃, yielding an electronic state assignment and excited state vibrational frequencies. Fragmentation in dimer ionization via theE state at 249 nm establishes the dissociation energy of Ag ₂ ⁺ to be <2.1 eV.     

Potentiometric determination of the ionization constants of ethylenediamine-N,N′-diglutaric acid at 298.15 K

Step ionization constants of ethylenediamine-N,N′-diglutaric acid at 298.15 K and ionic strength values of 0.1, 0.5, and 1.0 (KNO₃) are determined by means of potentiometry. The resulting data are extrapolated to zero ionic strength using an equation with one individual parameter, and the thermodynamic ionization constants are calculated. A correlation is made between the obtained results and the corresponding data for related compounds.     

Charge transfer complexes beneficial method for determination of fluoxetine HCl pure drug: Spectroscopic and thermal analyses discussions

A simple and conventional spectrophotometric method is developed for quantitative analysis of fluoxetine. The method is based on the charge transfer 1: 1 complex formation of fluoxetine hydrochloride with electron acceptors: picric acid, dinitrobenzene, p-nitrobenzoic acid, 2,6-dichloroquinone-4-chloroimide, 2,6-dibromoquinone-4-chloroimide and 7,7′,8,8′-tetracyanoquinodimethane. The charge-transfer complexes are isolated and characterized by elemental analysis, conductivity, IR, Raman, ¹H NMR spectra, X-ray powder diffraction, scanning electron microscopy and thermogravimetric analysis. The formation constants (K _CT), molar extinction coefficients (?_CT), standard free energies (ΔG ⁰), oscillator strengths (f), dipole moments (μ), resonance energies (R _N) and ionization potentials (I _D) are estimated. Thermodynamic parameters were computed from the thermal decomposition data.     

Charge location and fragmentation under electron impact. IV—the behaviour under electron impact of some N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds

The ionization potentials of a series of N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds have been determined. The nature of the highest occupied orbital of the molecules and the use of empirical rules to rationalize the variations in the ionization potentials are discussed. The changes in the fragmentation patterns are related to the different low ionization potential site(s) in each molecule. The occurrence of various rearrangement ions are discussed on a similar basis.     

NMR chemical shifts and coupling constants of various nuclei of N,N-diethylbenzenesulfenamide,N,N-diethylbenzeneseleneamide and some related sulfur amides

The ⁷⁷Se, ¹⁵N, ¹³C and ¹H NMR parameters have been determined for N,N-diethylbenzenesulfen- and N,N-diethylbenzeneseleneamide and the ¹H¹³C coupling constants additionally for N,N-dimethylmethanesulfinamide, N,N-dimethylbenzenesulfinamide, N,N-dimethylmethanesulfonamide, N,N-dimethylbenzenesulfonamide and diphenylsulfone. The nitrogen-15 nucleus is slightly more shielded in the sulfenamide than in the seleneamide. Compared to sulfin- and sulfonamides the nitrogen nuclei of these amides are more shielded. The solvent effects on the chemical shift of both selenium-77 and nitrogen-15 nuclei are observable. The nitrogen-15 chemical shifts of sulfur and seleneamides are less sensitive to the solvents than those of carboxamides. This change in the nitrogen-15 chemical shift in sulfen- and seleneamide is the same order of magnitude, but opposite in direction compared with that in sulfon- and sulfinamides. The ¹H¹³C direct aromatic coupling constants increase along with the increasing oxidation state of sulfur in sulfur amides, being greatest in sulfonamides.     

Substituent effects on the redox properties and structure of substituted triphenylamines. An experimental and computational study

The peak oxidation potentials of a series of polysubstituted triphenylamines were found to be highly linearly correlated (R=0.995) with their ionization potentials as computed by density functional theory. The computations, as well as confirming previous experiments demonstrating the planar geometry of such substances around the central nitrogen atom, also demonstrate substantial resonance interactions between the central nitrogen atom and a nitro group located para or ortho to it; no such interaction is involved in the corresponding amine cation radicals. On the other hand, a methoxy group located para to the central nitrogen atom interacts strongly with the central nitrogen in the cation radical, but not in the neutral amine.     

Symmetry adapted versus symmetry broken wavefunctions: the 1s core level ions of O+2

It is shown that, for O₂, in a MC SCF determination of the core ionization potentials employing the full Molecular point group, very few (N-1)-particle configurations are required in order to account for the symmetry breaking in the corresponding Hartree-Fock calculations.     

Empirical regularities of atomic ionization potentials

Regularities of the averaged ionization potentials for atoms and ions containing up to 18 electrons are studied in detail. It is shown that a two-variable function constructed from the averaged ionization potentials for each subshell is linear with respect to the degree of ionization q and the occupancy k of the s^k or p^k subshell. One linearity includes previous findings as a special case, and the other introduces a new regularity for atomic ionization potentials. Existing atomic ionization potentials and electron affinities are analyzed employing the regularities, and improved values of these quantities as well as term and fine structure separations in negative ions are derived.     

Small can be different

Theoretical investigations of size evolutionary patterns for multiply charged anionic metal clusters and solvation of sodium in water clusters are discussed. For Na _N ^Z- clusters, energetic stability and electron decay channels are determined. Formation of a “surface Rydberg-like state” in Na(H₂O) _N , correlating with calculated and measured ionization potentials, is analyzed.     

Equilibria in aqueous solution between fe(ii) and n-methyliminodiacetic,n-ethyliminodiacetic and npropyliminodiacetic acids

The complex species formed in aqueous solution between Fe(II) and N-methyliminodiacetic acid (MIDA), N-ethyliminodiacetic acid (EIDA) and N-propyliminodiacetic acid (PIDA) were studied at 25°C and ionic strength 0.1 M in KCl. The experimental potentiometric data were analysed with the least-squares computer program LETAGROP, taking into account hydrolysis of the Fe(II) ion. The ionization constants of MIDA, EIDA and PIDA acids are determined for the corresponding ionic strength and temperature. The following complex species were found (ligands, H₂C): MIDA, [FeHC]⁺, FeC and [FeC₂]_2–; EIDA, FeC and [FeC₂]_2–; PIDA, FeC, [FeC₂]_2– and [Fe(OH)C]_–. The corresponding stability constants were determined.     

Charge-Transfer Complexes between Substituted Pyridine N-Oxides and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

Spectrophotometry was used to study charge-transfer complexes between substituted pyridine N-oxides and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Vertical ionization potentials of pyridine N-oxides in the gas phase and in solution were calculated by the CNDO/S3' method. The calculated ionization potentials in chloroform nicely correlate with the experimental charge-transfer wavelengths of the complexes.     

Influence of diluent on radiolysis of amides in organic solution

The radiolytic behavior of N,N,N′,N′-tetraoctyldiglycolamide, N,N′-dimethyl-N,N′-dioctyl-2-(3′-oxapentadecyl)malonamide, and N,N-dioctylhexanamide in n-dodecane was investigated by irradiation with γ-rays and electron pulses. The results showed n-dodecane has a sensitization effect on the radiolysis of these amides, owing mainly to a charge transfer from radical cations of n-dodecane to the amide molecules in the primary process observed in pulse radiolysis. This result was supported by the difference in the ionization potentials between n-dodecane and these amides.     

Die elektrochemische oxidation aliphatischer nitroxyl-radikale

The electrochemical oxidation of seven different nitroxyl radicals has been investigated in acetonitrile at a platinum electrode. Cyclic and bicyclic nitroxyls are oxidized in a reversible one-electron-step to the corresponding oxammonium ions. From oxidation and ionization potentials the electrostatic solvation enthalpies of two oxammonium ions were calculated. The ionization potentials of the remaining compounds could be estimated. Heterogenous rate constants of the electrode reaction have been determined.     

Pairing effects in metal clusters

Motivated by the experimental finding of oddeven alternations in the mass spectra and ionization potentials of metal clusters, we have investigated the possibility of interpreting these results as evidence for pairing correlations among the electrons. For the present exploratory calculations, we have used a spherical BCS model which we have applied, as an example, to some Al clusters. Additional model calculations have been carried out for Na _N with 34<N<100 in order to illustrate a possible systematics.     

Protolytic properties of 2-acylthioacetamides

Concentration acidity of 2-acylthioacetamides dissolved in DMSO-H₂O was measured by the method of pH-metric titration. The data obtained were extrapolated for the determination of pK _a values of 2-acylthioacetamides in water and DMSO. We found that in aqueous solutions the acidity of thioacetarylamide (pK _a = 5.75?C6.01) was almost independent of the nature of substituents in their N-phenyl rings, whereas in DMSO solution the nature of substituents significantly affects their ionization constants (pK _a = 7.88?C11.70). The graphs were displayed and the acidity of N-aryl-3-oxobutanethioamides dependence on the Hammett constants of meta- and para-substituents in the phenyl rings derived. Water is shown to be a leveling, and DMSO a differentiating solvent for 2-acylthioacetamides.