The minimal basis set MINI-1—powerful tool for calculating intermolecular interactions. II. Ionic complexes

Optimum geometries and stabilization energies are determined for complexes of H₂O, NH₃, CH₄, C₂H₄, CO, and N₂ with metal cations including Li⁺, Na⁺, K⁺, Rb⁺, Be²⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Al³⁺, for the complex (HO)₂PO ₂ ^– ...Mg²⁺ and for the complexes of water with F^–, Cl^–, and Br^– by SCF calculations employing the MINI-1 minimal gaussian basis sets. The Boys-Bernardi method was used to evaluate the superposition error. Comparison with the extended basis set results revealed that the MINI-1 set gives uniformly good results for a broad variety of ionic complexes and therefore should be preferred to other small basis sets.     

The interaction of water with sulfonium ions and the effects of hydration on the energetics of methyl group transfer: An ab initio molecular orbital study of the hydration of (CH3)3S+ and (CH3)2S+CH2CO2 −

The interactions of the sulfonium ions (CH₃)₃S⁺, (CH₃)₂S⁺CH₂CO₂ ^–, and (CH₃)₂S⁺-CH₂CH₂CO₂ ^– with up to four water molecules have been studied by ab initio molecular orbital methods. Complexes of (CH₃)₃S⁺ with one to three water molecules involve strong electrostatic sulfur-oxygen interactions; in contrast, the sulfide (CH₃)₂S interacts with water molecules via weak S-H hydrogen bonds, suggesting that methyl-group transfer from (CH₃)₃S⁺ in aqueous solution involves a significant alteration of the hydration pattern around the sulfur atom. Two conformers of (CH₃)₂S⁺CH₂CO₂ ^– were found that display sulfur-oxygen distances which are approximately 0.3 å less than the sum of the sulfur and oxygen van der Waals radii, indicating a strong intramolecular electrostatic interaction. For the complexes (CH₃)₂S⁺CH₂CO₂ ^–·nH₂O(n =1–4), water interacts primarily with the carboxylate group via hydrogen bonds, rather than electrostatically with the sulfur atom, although in complexes with the three- and four-water complexes, the proximity of the positively charged sulfur atom to the carboxylate group significantly alters the hydration pattern compared to that in the corresponding of complexes CH₃SCH₂CO₂ ^–· Thus, methyl transfer from (CH₃)₂S⁺CH₂CO₂ ^– to an acceptor in aqueous solution also involves substantial changes in the hydration pattern around the carboxylate group.     

Structural and dynamic investigations of aqueous clusters of Na+ and K+

Using computer modeling, we have studied Na⁺–24H₂O and K⁺–24H₂O clusters. We propose ion-water interaction potentials. We obtain structural, energy, and dynamic characteristics of the studied clusters. We show different mechanisms for exchange of water molecules surrounding the Na⁺ and K⁺ ions: single-particle in the case of Na⁺, and close to K⁺, along with single-particle exchange, a large percentage of multiparticle cooperative exchange of water molecules. This difference is explained by the different degrees of orientation of the water molecules surrounding these ions, by the presence of a unified deformed network of H bonds in the K⁺ cluster and its absence in the Na⁺ cluster. We propose a negative hydration mechanism for the K⁺ ion.Institute of General and Inorganic Chemistry, Russian Academy of Sciences. Institute of Physical Chemistry, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 96–104, March–April, 1993.     

Contracted well-tempered Gaussian basis sets in SCF calculations on the ground and excited electronic states of neutral and ionized diatomic molecules containing first-row atoms

Summary Calculations were done on ground and excited states of C₂, C ₂ ⁺ , C ₂ ^– , N₂, N ₂ ⁺ , O₂, O ₂ ⁺ , O ₂ ^– , CO, CO⁺, CO²⁺, and CO^– using contracted well-tempered basis sets. The (14s 10p) basis sets were augmented with threed, one or twof, and oneg functions. Total energies, orbital energies, and spectroscopic constants were compared with the best available computational data.     

Infrared and raman spectra,vibrational assignments,normal coordinate analysis,and ab initio calculations of methyltrifluoromethyldisulfide and bis(trifluoromethyl)disulfide

The infrared and Raman (3500-35 cm^–1) spectra of gaseous and solid methyltrifluoromethyldisulfide, CF₃SSCH₃, and bis(trifluoromethyl)disulfide, CF₃SSCF₃, have been recorded. Additionally, the Raman spectra of the neat liquids have been obtained and qualitative depolarization values have been measured. These vibrational data have been interpreted, for both molecules, on the basis that the C-S-S-C dihedral angle is approximately 90°. Vibrational assignments are given for both molecules and are supported by normal coordinate calculations utilizing ab initio Hartree-Fock gradient calculations with the 3-21G^* basis set to obtain the frequencies for the normal modes and potential energy distributions. The CH₃ and CF₃ torsional modes have been observed at 140 and 48 cm^–1, respectively, for CF₃SSCH₃, from which periodic barriers of 485 cm^–1 (1.39 kcal mol^–1) and 853 cm^–1 (2.44 kcal mol^–1), respectively, have been calculated. Complete equilibrium geometries have been determined for both molecules by ab initio calculations employing both 3–21G and 6–31G basis sets. The structural parameters for bis(trifluoromethyl)disulfide are compared to those suggested from electron diffraction studies. The results are compared to corresponding quantities obtained for some similar molecules.Taken in part from the thesis of M. M. Bergana which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Novel properties of molecular assemblies of isoprenoid surfactants

Unlike micelles of straight hydrocarbon chain-surfactants, isoprenoid surfactants, CH₃ [CH(CH₃)CH₂CH₂CH₂]₃ CH(CH₃)CH₂–R (R=CH₂N⁺ (CH₃)₃ Br^–, CH₂OPO₃H^– Na⁺, CH₂OSO ₃ ^– Na⁺, CO ₂ ^– Na⁺), gave large globular and cellular assemblies in water which could be observed directly by transmission electron microscopy; critical micelle concentration of 0.31.4×10^–3 M at 20°C, aggregation number of 215×10⁴, and diameter of 200–2000 Å. A basic structure of the assemblies was a thin layer with a thickness (about 30 Å) which was close to the molecular length of the surfactants. The assemblies were decomposed during gel column chromatography; viz., they were not as stable as the liposomes of lecithins. The morphology was discussed in conjunction with a steric effect of the isoprenoid chain.     

Quantum-Chemical Study of Alkyl Carbenium Ions in 100% Sulfuric Acid

A quantum-chemical study of neutral and protonated monoalkyl sulfates RHSO₄and [RH₂SO₄]⁺(where R = CH₃, C₂H₅, iso-C₃H₇, and tert-C₄H₉) is carried out. Calculations are performed using the Hartree–Fock method in the 6-31G** and 6-31++G** basis sets taking into account electron correlation according to the Müller–Plesset perturbation theory MP2/6-31+G*//6-31+G*. Protonated tert-butyl sulfate was also calculated by the DFT B3LYP/6-31++G** method. It was found that monoalkyl sulfates are covalent compounds, and the complete abstraction of alkyl carbenium ions from them has substantial energy cost: 196.4, 161.7, 150.8 and 136.0 kcal/mol, respectively. Protonated methyl and ethyl sulfates are also covalent compounds according to the calculation. They have lower but still high energies of heterolytic dissociation (65.0 and 33.5 kcal/mol, respectively). The energy of R⁺abstraction from protonated isopropyl sulfate is much lower: 23.6 kcal/mol. The main covalent state and the ion–molecular pair, which is a carbenium ion [C(CH₃)₂H]⁺solvated by the H₂SO₄molecule, have about the same energy. The ground state of protonated tert-butyl sulfate corresponds to the ion–molecular complex [C(CH₃)⁺ ₃H₂SO₄] with still lower energy of carbenium ion [C(CH₃)₃]⁺abstraction, which is equal to 10.0 kcal/mol. Calculation according to the DFT B3LYP/6-31++G** method shows the absence of a minimum for the protonated tert-butyl sulfate with a covalent structure on the potential energy surface.     

Catalyzed Peptide Bond Formation in the Gas Phase. Role of Bivalent Cations and Water in Formation of 2-Aminoacetamide from Ammonia and Glycine and in Dimerization of Glycine

The formation of 2-aminoacetamide from ammonia and glycine and N-glycylglycine from two glycine molecules with and without Mg²⁺, Cu²⁺, and Zn²⁺ cations as catalysts have been studied as model reactions for peptide bond formation using the B3LYP functional with 6–311+G(d,p) and 6–31G(d) basis sets. The B3LYP method was also used to characterize the nine gas–phase complexes of neutral glycine, its amide (2-aminoacetamide), and N-glycylglycine with Lewis acids Mg²⁺, Cu²⁺, and Zn²⁺, respectively. Further, the gas-phase hydration of metal-coordinated complexes of glycine, 2-aminoacetamide, and N-glycylglycine was also investigated. Finally, the effect of water on the structure and reactivity of the metal coordinated complexes was determined. Enthalpies and Gibbs energies for the stationary points of each reaction have been calculated to determine the thermodynamics of the reactions investigated. A substantial decrease in reaction enthalpies and Gibbs energies was found for glycine–ammonia and glycine–glycine reactions coordinated by Mg²⁺, Cu²⁺, and Zn²⁺ ions compared to those of the uncoordinated 2-aminoacetamide bond formation. The formation of a dipeptide is a more exothermic process than the creation of simple 2-aminoacetamide from glycine. The energetic effect of the transition metal ions Cu²⁺ and Zn²⁺ is of similar strength and more pronounced than that of the Mg²⁺ cation. The basicity order of the amides investigated shows the order: NH₂CH₂CO₂H < NH₂CH₂CONH₂ < NH₂CH₂CONHCH₂CO₂H. Interaction enthalpies and Gibbs energies of metal ion–amide complexes increase as Mg²⁺2+2+. In both reactant (glycine) and reaction products (2-aminoacetamide, N-glycylglycine) dihydration caused considerable reduction (about 200–500 kJ-mol^–1) of the strength of the bifurcated metal–amide bonds. Solvent effects also reduce the reaction enthalpy and Gibbs energy of reactions under study.     

Synthesis of an intercalated compound of montmorillonite and 6-polyamide

Natural montmorillonite, fractionated from bentonite produced in Yamagata, Japan, was ion-exchanged for NH ₃ ⁺ –(CH₂)₁₁–COOH, NH ₃ ⁺ –(CH₂)₅–COOH, Al³⁺, Cu²⁺, Mg²⁺, Co²⁺, Li⁺, K⁺ and H⁺. The mixtures of the ion-exchanged montmorillonite and -caprolactam were heated at 263°C in glass ampoules for various periods. The intercalated compounds before and after the heating were examined by X-ray powder diffraction, DSC and GPC. Although -caprolactam was not polymerized without montmorillonite, it was polymerized at 263°C in the presence of montmorillonite. The polymerization rate varied with the interlayer cations in the order of NH ₃ ⁺ –(CH₂)₁₁–COOH>Al³⁺>NH ₃ ⁺ –(CH₂)₅–COOH>H⁺>Cu²⁺>Mg²⁺>Co²⁺>Li⁺>K⁺. After heating at 263°C for 5 h, the mean number-average molecular weight was about 1.5×10⁴. Although the interlayer distance of NH ₃ ⁺ –(CH₂)₁₁–COOH type montmorillonite/-caprolactam compound increased from 2.85 nm to 4.90 nm by heating at temperatures above the melting point of -caprolactam, those of other compounds were not changed. After heating at 263°C, an intercalated compound of montmorillonite and 6-polyamide, whose interlayer distance was more than 10 nm, was obtained. It is concluded that montmorillonite acts as a Brönsted acid and initiates the open ring polymerization of -caprolactam and that the driving force of swelling is the polymerization energy.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Conformational Studies of Methyl Vinyl Silane from Temperature-Dependent FT–IR Spectra of Xenon and Krypton Solutions

Variable-temperature (–55 to –155°C) studies of the infrared spectra (3500–400 cm^–1) of methyl vinyl silane, CH₂CHSiH₂CH₃, dissolved in liquid xenon and krypton have been recorded. Utilizing three sets of conformer doublets due to the cis and gauche rotamers, the enthalpy difference has been determined to be 133 ± 11 cm^–1 (1.59 ± 0.13 kJ/mol) with the gauche conformer the more stable form in the krypton solution. In the xenon solution, the enthalpy difference could not be determined because the infrared bands become so broad and the overlap was so extensive that meaningful areas could not be determined. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G(2d,2p) from which structural parameters and conformational stabilities have been determined. With the largest basis set, the cis conformer is predicted to be the more stable conformer, which is inconsistent with the experimental results. Utilizing previously reported microwave rotational constants for both conformers along with the ab initio predicted distances and angles, r ₀ parameters have been obtained for both the cis and gauche conformers. The spectroscopic and theoretical results are compared to the corresponding quantities for some similar molecules.     

Quantitative chemical analysis on paper: Determination of phosphate in the presence of large quantities of other ions

Summary A rapid method has been developed for the determination of phosphate by means of filter paper impregnated with lead iodide. A sample is added to the impregnated filter paper by means of a capillary, and after irrigation to cause migration of the ions a white spot is obtained as the lead iodide is converted into the phosphate. The weight of the spot is dependent on the p_H and the quantity of phosphate present.The determination is possible in the presence of SCN^–, Cl^–, Br^–, NO₃ ^–, CO₃ ^–, I^–, IO₃ ^–, CH₃COO^–, B₄O₇ ^2–, F^–, Sb₂O₇ ^4–, K⁺, Na⁺, NH₄ ⁺, OH^–, H⁺, succinic, citric and tartaric acids. The determination is impossible in the presence of C₂O₄ ^2–, SO₄ ^2–, MoO₄ ^2–, NO₂ ^–, SO₃ ^2–, S^2–, CrO₄ ^2–, or CO₃ ^2–.The method permits the determination of 7–100g of phosphate with an accuracy of 2%.

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Zusammenfassung Ein schnelles Verfahren zur Phosphatbestimmung wird besehrieben, bei dem man sich eines mit Bleijodid imprägnierten Filterpapiers bedient. Die Probe wird mit einer Kapillare auf das Papier aufgebracht. Man erleichtert die Ionenbewegung durch geeignete Befeuchtung und erhält einen weißen Fleck infolge Umsetzung des Bleijodids in -phosphat. Das Gewicht des Fleckens hängt vom p_H und von der Phosphatmenge ab.Die Bestimmung ist möglich in Gegenwart von SCN^–, Cl^–, Br^–, NO₃ ^–, CO₃ ^–, J^–, JO₃ ^–, CH₃COO^–, B₄O₇ ^2–, F^–, Sb₂O₇ ^4–, K⁺, Na⁺, NH₄ ⁺, OH^–, H⁺, Bernsteinsäure, Zitronensäure und Weinsäure; sie ist nicht möglich bei Gegenwart von C₂O₄ ^2–, SO₄ ^2–, MoO₄ ^2–, NO₂ ^–, SO₃ ^2–, S^2–, CrO₄ ^2– oder CO₃ ^2–. 7 bis 100g Phosphat können mit einer Genauigkeit von 2% bestimmt werden.

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Résumé On a développé une méthode rapide pour le dosage des phosphates sur papier-filtre imprégné d'iodure de plomb. On dépose l'échantillon sur le papier-filtre imprégné, à l'aide d'un capillaire, et, après humidification pour provoquer la migration des ions, on obtient une tache blanche quand l'iodure de plomb est converti en phosphate. Le poids de la tache dépend du p_H et de la quantité de phosphate présent.Le dosage est possible en présence de SCN^–, Cl^–, Br^–, NO₃ ^–, CO₃ ^–, I^–, IO₃ ^–, CH₃COO^–, B₄O₇ ^2–, F^–, Sb₂O₇ ^4–, K⁺, Na⁺, NH₄ ⁺, OH^–, H⁺, et des acides succinique, citrique et tartrique. Il est impossible en présence de C₂O₄ ^2–, SO₄ ^2–, MoO₄ ^2–, NO₂ ^–, SO₃ ^2–, S^2–, CrO₄ ^2– ou CO₃ ^2–.La méthode permet le dosage de 7 à 100g de phosphate avec une précision de 2%.

     

Analytic evaluation of infrared intensities and polarizabilities by two-configuration self-consistent field wave functions

For more than a few molecular electronic states, the simplest qualitatively correct picture of the electronic structure is provided by the two-configuration self-consistent-field (TCSCF) method. Here, analytic methods are reported for the evaluation of TCSCF infrared intensities and polarizabilities. These new methods have been implemented and applied to the molecules CH₂(¹A₁), CF₂, CH ₃ ^– , NH₃, HF and O₃. Nine different basis sets, ranging from 3–21G to triple zeta plus double polarization (TZ + 2P), have been used. In several cases one finds qualitative differences between the analogous SCF and TCSCF predictions.     

Reexamination of the C2H4F potential surface. the status of the classical 2-fluoroethyl cation: a local minimum or transition structure?

According to ab initio molecular orbital calculations carried out with full geometry optimization at the MP2/6–31G^** level, the classical 2-fluoroethyl cation, FCH₂CH₂⁺, is a transition structure for H-scrambling in CH₃CHF⁺. Single point MP4/6–31G^** calculations at the optimized geometries predict the cyclic ethylene fluoronium ion to lie 24.2 kcal mol⁻¹ above CH₃CHF⁺ and 5.4 kcal mol⁻¹ below the 2-fluoroethyl cation. ΔG‡ for ring opening of the cyclic fluoronium ion at -60° is estimated to be ca 15 kcal mol⁻¹. This barrier is largely attributable to the powerful negative fluorine hyperconjugation in the transition state as described by Hoffmann and coworkers. When electron correlation effects are ignored a qualitatively different potential surface is obtained on which the 2-fluoroethyl cation is calculated to be a local minimum separated from the stable 1-fluoroethyl cation by an H-bridged transition state.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.     

The O–H···O, O–H···N and C–H···O hydrogen bonds in 1,4-dimethylpiperazine mono-betaine monohydrate

1,4-Dimethylpiperazine mono-betaine (1-carboxymethyl-1,4-dimethylpiperazinium inner salt, MBPZ) crystallizes as monohydrate. The crystals are orthorhombic, space group Pccn. Two MBPZ molecules and two water molecules form a cyclic oligomer, (MBPZ·H₂O)₂. The O–H···O and O–H···N hydrogen bonds are of 2.769(1) and 2.902(1) Å, respectively. The dimers interact with the neighboring molecules through the C–H···O hydrogen bonds of 3.234(1) Å. The piperazine ring assumes a chair conformation with the N(4)–CH₃ and N⁺(1)–CH₂COO⁻ groups in the equatorial position and the N⁺(1)–CH₃ group in the axial one. The FTIR spectrum is compared with that calculated by the B3LYP/6-31G(d,p) level of theory.     

On the chemical resolution of the 87Rb+ (s0)/87Sr+ (s1) isobaric interference: a kinetic search for an optimum reagent

Room-temperature reactions of the atomic cations Sr⁺ and Rb⁺ have been surveyed systematically with a variety of gases using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions have been measured in He buffer gas at 0.35 Torr and 295 K for reactions of Sr⁺ and Rb⁺ with CH₃F, CH₃Cl, N₂O, CO₂, CS₂, SF₆, D₂O and NH₃. Rb⁺ (s⁰) is seen to be quite inert with these molecules and reacts either slowly by molecule addition or not at all, while Sr⁺ (s¹) is much more reactive with all these 8 molecules, especially with CH₃F, CH₃Cl, N₂O and SF₆. Sr⁺ reacts with CH₃F and SF₆ by F-atom transfer, with CH₃Cl by Cl-atom transfer and with N₂O by O-atom transfer, and the reaction rate coefficients are all quite high, k ≥ 1.4 × 10⁻¹¹ cm³ molecules⁻¹ s⁻¹. The extreme differences in reactivity with CH₃F, SF₆, CH₃Cl and N₂O provide a chemical basis for the separation of isobaric interferences of ⁸⁷Rb⁺ and ⁸⁷Sr⁺ often encountered in ICP-MS. Among these four molecules, SF₆ exhibits the largest difference in reactivity, almost a factor of 10⁴, and so is identified as the kinetically recommended reagent for the chemical resolution of the isobaric interference of ⁸⁷Rb⁺ and ⁸⁷Sr⁺.     

Basis-independent potential energy curves for the neutral diatomics of Li,Na and K evaluated by means of Hartree-Fock and different density functional potentials

Summary The solution of the Schrödinger equation for diatomic molecules when the finite element method is used gives the possibility to evaluate highly accurate basis-independent potential energy curves. In this work such types of numerically accurate potential energy curves on the HF level have been evaluated for Li₂, Na₂ and K₂ and could be used as benchmarks in the optimization of basis sets. A comparison between recent LCAO HF calculations in which extended basis sets are used and the accurate values determined in this work show that there is a difference in total energy of 4×10^–5 and 10^–3 a.u. for Li, Li₂, and Na, Na₂, respectively. Evaluated dissociation energies are, however, due to the cancellation of numerical errors in much better agreement. Further, it is found that different exchange correlation potentials for the heavier molecules such as those given by von Barth-Hedin and Vosko, Wilk and Nusair reproduce experimental properties such as dissociation energies, vibrational frequencies almost as well as those achieved with advanced CI methods. TheX potential gives accurate bond lengths for Na₂ and K₂, whereas the dissociation energies are too small.     

Mass spectrometric study of methyl-substituted 4-azaphenanthrenes and their nitration products

The mass spectral behavior of five derivatives of the 4-azaphenanthrene series — 1,3-dimethyl-(I), 2,3-dimethyl-(II), 1,2,3,-trimethyl-(III), 1,2,3-trimethyl-8-nitro-(IV), and 1,3-dimethyl-6,7-dinitro-4-azaphenanthrene (V) — was studied. The stabilities of the molecular ions with respect to gragmentation (W_M) are higher by a factor of two or more for the methyl-substituted I–III than for nitro derivatives IV and V. The intensity of the [M-H]⁺ ion peak in the mass spectra of I–V does not depend on the number of methyl groups but only on their positions: the presence of a CH₃ group in the 2 position leads to an [M-H]⁺ ion that is 1.5 times more intense than when there is a methyl group in the 1 position. The molecular ions of I–V do not eliminate HCN molecules; this constitutes evidence for the absence of randomization of their methyl groups. The presence of a CH₃ substituent in the 1 or 2 position does not affect the intensity of the [M-CH₃]⁺ ion peaks, while the simultaneous presence of CH₃ groups attached to the C₁ and C₂ atoms increases the intensity of the [M-CH₃]⁺ fragment peak by a factor of two. In the mass spectra of nitro derivatives IV and V, [M-O]⁺, [M-OH]⁺, [M-NO]⁺, and [M-NO₂]⁺ fragments are observed in the first step of the fragmentation of the M⁺ ion, whereas the [M-CO]⁺ ion peak characteristic for the dissociative ionization of 1-nitronaphthalene is also observed for 8-nitro-substituted IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1365–1369, October, 1977.     

Ab initio calculations of activation energy of the reaction of hydrogen exchange on strongly acidic centers

Ab initio calculations of fragments of the potential energy surfaces of hydrogen exchange reactions between H₂, CH₄, and alanine molecules and the H₃O⁺ ion were performed by the restricted Hartree-Fock method, at the second-order Møller-Plesset level of perturbation theory, and by the method of coupled clusters using the 6–31G^* and aug-cc-pVDZ basis sets. The one-center synchronous mechanism of hydrogen exchange reaction was studied and the activation energies and structures of transition states were determined. It was found that the geometric parameters of the H₂ and CH₄ molecules in the transition states are close to those of the H₃ ⁺ and CH₅ ⁺ ions. The higher the proton affinity of the reacting molecule in the reaction studied the lower the activiation energy of hydrogen exchange. The one-center mechanism studied can be used to describe the high-temperature solid-state catalytic isotope exchange (HSCIE) reaction. The results ofab initio calculations of synchronous hydrogen exchange between the H₃O⁺ ion and hydrogen atoms in different positions of the alanine molecule are in good agreement with experimental data on the regioselectivity and stereoselectivity of the HSCIE reaction with spillover-tritium.     

Effect of the Supporting-Electrolyte Cation on the Chloroplatinite Ion Reduction at a Dropping Mercury Electrode

The effect of nature and concentration of supporting-electrolyte cations (Li⁺, Na⁺, Cs⁺, (CH₃)₄N⁺, Ca²⁺, Ba²⁺) on electroreduction kinetics of PtCl^2- ₄at a dropping mercury electrode is studied. The electroreduction wave for PtCl^2- ₄is complicated by a polarographic maximum of first kind followed by a pronounced plateau of limiting current, after which the current passes through a minimum. The electroreduction occurs probably via two different mechanisms and presumably involves the same species, because the charge z _iof discharging species, determined by the Frumkin–Petrii method, remains virtually constant (z _i –1) on both descending (E= –0.6 to –1.0 V vs. SCE) and ascending (–1.3 to –1.6 V) branches of polarization curves and is independent of the nature of the supporting-electrolyte cation. The mechanism is presumably changed by a changed orientation of discharging species relative to the electrode surface.