A quantum chemical study of the hydrogen bonding in the CO2⋯HF and N2O⋯HF complexes

Summary Quantum chemical ab initio calculations have been performed for the complex CO₂HF and N₂OHF. The interaction energies were computed through fourth order MBPT and were corrected for basis set superposition errors. Extended polarized basis sets were used which are constructed to give accurate values for electric moments and polarizabilities. The complex NNOHF was found to be bent, while OCOHF is linear, in agreement with experiment. The MBPT calculations give evidence for a second linear isomeric structure FHNNO, a possibility which has also been suggested by recent experimental data. The computed binding energies are: 2.5 kcal/mol for OCOHF, 2.4 kcal/mol for NNOHF, and 3.0 kcal/mol for FHNNO. At the SCF level, the FHNNO complex is less stable than NNOHF, but correlation has a large effect on the geometry and energetics of the latter complex. The NNOHF complex seems to be a system where the positive intramolecular correlation correction prevails over the negative intermolecular component.     

The structure and harmonic vibrational frequencies of the weakly bound complexes formed by HF with CO,CO2 and N2O

The structure and harmonic vibrational frequencies of several weakly bound complexes formed by HF are reported. Theab initio MP2 approach is used with large basis sets for the optimisation of geometries and the determination of harmonic frequencies. COHF and OCHF are examined; both are found to be minima, with the latter being the dominant structure. The linear OCOHF andT shaped OCOFH are studied, but only the linear structure is a minimum. N₂OHF has two minima on the surface corresponding to bent NNOHF and linear ONNHF structures.     

The influence of Na+ on neighbouring hydrogen bonds of aliphatic amino acid

Summary The influence of Na⁺ on hydrogen bonds of the OH O and NH O type between an aliphatic amino acid (glycine zwitterion) and water is investigated byab initio calculations with minimal Gaussian basis sets. Distortion of the hydration shell caused by Na⁺, and interaction energies contributing to the over-all stabilization are discussed.

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Der Einfluß von Na⁺ auf die benachbarten Wasserstoffbindungen in aliphatischen Aminosäuren

Zusammenfassung Der Einfluß von Na⁺ auf die Wasserstoffbindungen vom OH O- und NH O-Typ in aliphatischen Aminosäuren (Glycin-Zwitterion) und Wasser wurde mittelsab initio Berechnungen mit einem minimalen Gausschen Basissatz untersucht. Die durch Na⁺-Ionen hervorgerufenen Verzerrungen der Hydratationsschale und die zur Gesamtstabilisierung beitragenden Wechselwir-kungsenergien werden diskutiert.

     

Aminomethylene derivatives of azoles

4-Aminoethylidene and 4-aminomethylene derivatives of 5-imidazolone exist in the enamine form as two isomers that are stabilized by intramolecular hydrogen bonds of the NHN and NHO type. In solution the enamine with a five-membered H ring is gradually converted to the corresponding isomer with a six-membered H ring with an NHO bond. Because of steric hindrance, rotation about the carbon-carbon double bond is realized more slowly in the aminoethylidene derivatives than in the aminomethylene derivatives of 5-imidazolone.See [1] for communication XXI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1677–1679, December, 1978.     

Thermal decomposition of rare earth salicylates in air atmosphere

The conditions of decomposition of Y, La and lanthanide (from Ce(III) to Lu) salicylates have been studied. On heating, the hydrated salicylates of Y and lanthanides from Nd to Lu lose crystallization water in one step to yield the anhydrous salts. The anhydrous complexes of Y, La, Ce(III), Pr, Nd, Sm, Eu(III), Gd and Tb subsequently decompose in several steps to the oxides Ln₂O₃, CeO₂, Pr₆O₁₁ and Tb₄O₇. The anhydrous complexes of the remaining lanthanides decompose directly to the oxides Ln₂O₃.

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Zusammenfassung Die Zersetzungsreaktionsbedingungen von Y-, La- und Lanthanid-(Ce(III) bis Lu) salizylaten wurden untersucht. Beim Erhitzen geben hydrierte Salizylate von Y und der Lanthanide Nd bis Lu Kristallwasser in einem Schritt ab und bilden wasserfreie Salze. Die wasserfreien Komplexe von Y, La, Ce(III), Pr, Nd, Sm, Eu(III), Gd und Tb zersetzen sich in mehreren Schritten und bilden die Oxide Ln₂O₃, CeO₂, Pr₆O₁₁ und Tb₄O₇. Die wasserfreien Komplexe der übrigen Lanthaniden zerfallen direkt in Ln₂O₃ Oxide.

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, . , . , , , , , , , , Ln₂O₃, CeO₂, Pr₆O_{11 47}. Ln₂O₃.

     

Crystal and molecular structure analysis of flutamide. Bifurcated helicoidal C-H ⋯ O hydrogen bonds

Crystal structure determination and semiempirical AM1 and PM3 calculations were performed on flutamide {2-methyl-N[4 nitro-3-(trifluoromethyl) phenyl] propamide}, a powerful nonsteroidal androgen antagonist. The molecule is almost planar apart from CF₃, NO₂, and CH₃ groups. The NO₂ plane makes an angle of 36.3(4) with the least-square plane of the phenyl ring. The molecules are intermolecularly linked by one N-H O and one C-H O hydrogen bonds. A bifurcated helicoidal hydrogen bond network is formed by the intermolecular C-H O hydrogen bond together with another intramolecular C-H O hydrogen bond. The calculated structures are in good agreement with the crystallographic conformations. AM1 is more accurate for predicting the intramolecular C-H O hydrogen bond while PM3 gives a better geometry for the crowded nitro group. AM1 and PM3 charges of benzenic hydrogens are used to predict the propensity of these atoms to form hydrogen bonds. The noncentrosymmetric space group of the crystal (Pna2₁), the calculated dipole moment (8.88 D), and the calculated angle between molecular dipoles and the twofold axis (–49) close to the optimal value (54.7) indicate that flutamide might be a possible candidate for nonlinear optical material.     

Hydrogen bond lengths in aqueous hydroxylammonium nitrate as a function of concentration,temperature and pressure

Qualitative and quantitative information about the interspecies distance distributions in aqueous hydroxylammonium nitrate (HAN) is obtained as a function of concentration (7 to 17M), temperature (–120 to 60°C) and pressure (0.1 to 7100 MPa) using isotopic uncoupling techniques for the O-HO and N-HO hydrogen bonds in conjunction with frequency-distance correlations.     

Catalytic properties of sodium-containing silica gel in n-heptane decomposition

n-Heptane decomposition reactions on silica catalysts containing various amounts of sodium ions were studied. Ethylene, methane and propylene as well as unbrached -olefins were the main reaction products. The comparison of the experimental and theoretical results suggests a free-radical reaction mechanism.

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- , . , , -. - .

     

Kinetics and mechanism of the reaction of 1,2-diethoxyethane hydroperoxide with ozone

The kinetics and products of the reaction of 1,2-diethoxyethane hydroperoxide with ozone in CCl₄ solution at 9 and 22°C have been studied. A reaction mechanism is proposed.

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I,I- CCl₄ (9; 22°C). .

     

Untersuchung und Bestimmung des Wassergehalts von feindispersen Kieselsäuren

Zusammenfassung Ziel der Arbeit war die Entwicklung einer Schnellmethode zur Bestimmung des Wassergehaltes von in der Gummiindustrie als Füll- und Verfestigungsstoffe angewandten Silikaten. Da diese das Wasser teils adsorptiv, teils chemisch gebunden enthalten, wurde durch IR-Untersuchungen verfolgt, wie sich bei unterschiedlichen Bedingungen die Art der Bindung des Wassers verändert. Das physikalisch gebundene Wasser wurde thermometrisch bestimmt. Diese Methode beruht darauf, dass die Wärmetönung der Reaktion zwischen Karl-Fischer-Lösung und Wasser stark exotherm ist und im adiabatischen Kalorimeter die Temperaturveränderung unter geeigneten Bedingungen proportional dem Wassergehalt ist.

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The aim of the present work was to develop a rapid method for moisture determination in silicic acid used in rubber industry as a reinforcer and ingredient. Water is bound in silicic acid by chemical and adsorption forces. The changes in the nature of the bond under different conditions were studied by infrared spectroscopy.The amount of the physically bound water was determined by direct thermometry (DIE). The method is based on the phenomenon that the heat of reaction between the Karl Fischer reagent and water is great, and that in an adiabatic calorimeter under appropriate conditions the temperature change is proportional to the water content of the samples.

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, . . . . , .

     

Structure of the Molecular Complexes of 18-Crown-6 with 1,2,5-Oxadiazole Derivatives

This paper reports on an X-ray diffraction analysis of host–guest type molecular complexes of 18-crown-6 with 1,2,5-oxadiazole derivatives: ethyl 4-amino-1,2,5-oxadiazole-3-carboxylic ether (1:1) (complex I), 4-(2-chloroethylamino)-1,2,5-oxadiazole-3-carboxylic acid hydrazide (1:2) (complex II), and 4-amino-1,2,5-oxadiazole-3-carboxylic acid amide monohydrate (1:1:1) (complex III). Crystals I are monoclinic with cell parameters a = 8.960(2), b = 18.118(4), c = 14.405(3) , = 106.9(3)°, space group P2₁/n, R = 0.054 for 4082 reflections. The 18-crown-6 and guest molecules are linked by hydrogen bonds of NHO(crown) and CHO(crown) types based on the head-to-tail principle, alternating in infinite chains along the y axis in the crystal. Crystals II are triclinic with cell parameters a = 8.615(2), b = 9.249(2), c = 10.987(2) , = 106.86(3), = 95.25(3), = 97.74(3)°, space group P1, R = 0.046 for 3006 reflections. The guest molecules are united into dimers by N–HO=C hydrogen bonds. The 18-crown-6 molecules and the dimer associates of the guest form chains along [110] in the crystal. Crystals III are monoclinic with cell dimensions a = 13.238(3), b = 19.004(4), c = 8.485(2) , = 100.75(3)°, space group Cc, R = 0.051 for 2032 reflections. The crown ether molecule is disordered over two positions. The NHO=C and NHN type hydrogen bonds link the guest molecules into chains. The water molecules serve to bridge the chains with crown ether molecules, forming ribbons whose axis lies along the z direction in the crystal.     

The geometry of intermolecular interactions in some crystalline fluorine-containing organic compounds

The propensity of C-F groups to form C-F H-C interactions with C-H groups on other molecules has been analyzed. Crystal structures of molecules containing only carbon, hydrogen, and fluorine, but no oxygen, nitrogen, or other hydrogen-bond-forming elements, were chosen for an initial study in which the intermolecular interactions in crystal-structure determinations of polycyclic aromatic hydrocarbons and their analogous fluoro derivatives were analyzed. It is found that C-F H-C interactions occur, but they are weak, as judged by the intermolecular distances and the angles involved. In a study of crystal structures of molecules containing other elements in addition to carbon, hydrogen, and fluorine, it was found that when an oxygen atom is in a neighboring position on an interacting molecule, a C-O group is more likely than a C-F group to form a linear interaction to the hydrogen atom of a C-H group. Thus, in spite of the high electronegativity of the fluorine atom, a C-F group competes unfavorably with a C-O^–, C-OH, or C=O group to form a hydrogen bond to an O-H, N-H, or C-H group. It is found, however, particularly for polycyclic aromatic hydrocarbons with substituted CF₃ groups that, in the absence of other functional groups that can form stronger interactions, C-F H-C interactions may serve to align molecules and give a different crystal packing from that in the pure hydrocarbon (where fluorine is replaced by hydrogen). Thus, C-F H-X (X = C, N, O) interactions are very weak, much weaker than C=O H-X interactions, but they cannot be ignored in predictions of modes of molecular packing in complexes and in crystals.     

Mutual Weakening of Hydrogen Bonds Between Hydrogen Fluoride and Proton Donors

The mutual effect of hydrogen bonds in BHF(HHal) _n complexes (Hal = F, Cl, Br, I; B = –, CH₃CN, NH₃; n = 1-3) was examined using the self-consistent field ab initio approach (6-31++G(d,p) and ECP-HW). When two and three equivalent H bonds are formed from the lone electron pairs of the fluorine atom of the HF molecule, the mutual weakening effect is 17% and 28%, respectively. The coefficients of the mutual effects of hydrogen bonds in HF(HHal)₂ and H₂O(HHal)₂ bridges are close in magnitude.     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

Characterization of silica supported PtFe catalysts by M?ssbauer spectroscopy

Mössbauer spectroscopy has been used to characterize silica supported PtFe bimetallic system with different iron loads. The partial reversibility in room temperature oxidation-reduction and the IS indicate direct PtFe contact on the support. At higher iron loads the Fe dispersity is increased and part of iron cannot be reduced, indicating the presence of non-alloyed iron.

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PtFe , . - PtFe . Fe , .

     

Hydrogen-bonded complexes involving HF and HCl: the effects of electron correlation and anharmonicity

Calculations on the hydrogen-bonded complexes HCNHF, H₂OHF, ClCNHCl and (CH₃)₂OHCl are reported. SCF harmonic values for the HF and HCl frequency shifts are in considerable disagreement with experiment, by as much as 100 cm^–1. Calculations at the MP2 (harmonic) level yield improved agreement with experiment, reducing discrepancies to the order of 10 cm^–1. We have also calculated all the cubic and quartic force constants for HCNHF at the SCF level, so that the anharmonic constants, x _rs can be evaluated. Although x ₁₁ (v ₁=H-F stretch) is large and negative, it is more than compensated by a positive x ₁₆ (v ₆=NH-F bend), so that the anharmonic correction to v ₁ is small and positive. The validity of these anharmonistudies is examined.     

Changes in the acid-strength distribution and the catalytic selectivity of H,Na?MOR

Acidities of synthetic H,Na–MOR samples decationized to different degrees have been characterized by differential adsorption heat distribution of ammonia. A fairly good correlation has been found between the number of acid sites of different strengths and the catalytic activity as well as the selectivity for xylene isomerization and disproportionation. The results are correlated with the mechanism of these reactions.

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H,Na–MOR, , - . , . .

     

A model of reaction front propagation in crystals

A spatio-temporal model of anisotropic propagation of the dehydration front in Na₃P₃O₉ · 6H₂O single-crystals is discussed. It is based on the assumption that dehydration proceeds as a periodic displacement of the reaction front from one reacting elementary block to another, and that experimentally fixed dehydration patterns are composed of a multitude of elementary patterns having the same shape. The model can be applied to other crystals.

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Zusammenfassung Ein Zeit- und Raummodell der anisotropischen Fortschreitung der Dehydratationsgrenzfläche in Na₃P₃O₉ · 6H₂O Einkristallen wird diskutiert. Das Modell ist auf einer Annahme begründet, dass die Wasserabspaltung als eine periodische Propagation der Reaktionsgrenzfläche von einem reagierendem Elementarblock zu anderem verläuft und dass die experimentell fixierte Entwässerungsfiguren aus einer Menge von Elementarfiguren von identischer Form zusammengestellt sind. Das Modell kann auf andere Kristallen verbreitet werden.

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- Na₃P₃O₉· 6₂. , , . .

     

Study of hydroisomerization of n-hexane on natural mordenite catalyst

A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.

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(), , , , -. Pt , .