An FTIR investigation of hexadecyltrimethylammonium intercalation into rectorite

Rectorite is an interstratified clay mineral made at 1:1 ratio of an orderly arrangement of a nonswelling component illite and a swelling component smectite. Due to the presence of two distinct types of components, it is of great interest to study the adsorption of long chain alkylammonium in rectorite. In this study, we conducted batch experiments and used X-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy to characterize the interlayer configuration of intercalated long chain hexadecyltrimethylammonium (HDTMA) in rectorite. The FTIR results showed that a monomer-like intercalation with extensive gauche conformers was formed at surfactant loading less than the cation exchange capacity (CEC) of the mineral. At a higher surfactant loading the CH2--symmetric and anti-symmetric vibrations shifted to lower frequencies, suggesting a more ordered all-trans surfactant interlayer configuration. The thermogravimetric and derivative of thermogravimetric analayses showed a high pyrolysis temperature for the monomer-like gauche conformers and lower pyrolysis temperature for the all-trans configuration of the intercalated HDTMA. The XRD analysis confirmed the monomer-like conformation with a d-spacing of 25.2 angstroms at the low surfactant intercalation and a vertical all-trans configuration with a d-spacing of 49.5 angstroms at an HDTMA intercalation of 3.20 CEC. In addition to conformation analyses of intercalated surfactant in the interlayer using FTIR, the absorbance measured by peak height at 1470, 2850, and 2917 cm(-1) increased linearly with surfactant loading, providing a faster, yet efficient method to quantify the amount of surfactant adsorbed.     

Quantum-chemical investigation into the geometric and energetic characteristics of kaolinite cluster models

A method of constructing molecular models for layered aluminosilicate crystals is put forward. The geometric and energetic characteristics of cluster models are calculated for the elementary kaolinite crystal layer using the MNDO approximation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 3, pp. 214–218, May–June, 1993.     

Quantum-chemical investigation of monosubstituted cyclopropanes

The applicability of the semiempirical MINDO/3 and MNDO methods is demonstrated for the determination of the relative changes in the strain of the three-carbon ring and examination of the contributions from the effects of substituents X to the stabilization energy of monosubstituted cyclopropanes (substituents H, OCH₃, NH₂, F, Cl, CH₃, CF₃, COCH₃, CN, NO₂). The best results, comparable with the data from nonempirical calculations, were obtained by the MINDO/3 method. The method correctly confers the changes in the geometry of substituted cyclopropane rings but systematically underestimates the strain energy by 20–40 kJ/mole. To judge from the AE_strain values, the -accepting effect of the substituents NO₂, COCH₃, and CN plays a major role in determining the electronic structure, suppressing the destabilizing -acceptor effect. In the case of the substituents F, Cl, OCH₃, and NH₂ the stabilizing -donor effect is either completely suppressed or is partly balanced by the -acceptor effect.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 21, No. 4, pp. 399–407, July–August, 1985.     

Electrochemical investigation of lithium intercalation into graphite from molten lithium chloride

Lithium reduction at a graphite electrode in molten lithium chloride was studied at temperatures from 650 to 900 °C using cyclic voltammetry and chronoamperometry. It was found that, during cathodic polarization, lithium intercalation into graphite occurred before deposition of metallic lithium started. This process was confirmed to be rate-controlled by the diffusion of lithium in the graphite. When the cathodic polarization potential was more negative than that for metallic lithium deposition, exfoliation of graphite particles from the electrode surface was observed. This was caused by fast and excessive accumulation of lithium intercalated into the graphite, which produced mechanical stress too high for the graphite matrix to accommodate. The erosion process was abated once the graphite surface was covered by a continuous layer of liquid lithium. These results are of relevance to the mechanism of carbon nanotube and nanoparticle formation by electrochemical synthesis in molten lithium chloride.     

Quantum-chemical investigation of tautomerism of hydrophosphoryl compounds

The tautomerization energies for the reaction R₂P(O)H R₂P-OH, where R= OH, OCH₃, OC₂H₅, CH₃, and CF₃, have been calculated by the CNDO/2 method with optimization of the exponents of the Slater 3d AO's according to the criterion of a minimum total energy for the molecule. The results are in qualitative agreement with the experimental data. The MNDO and CNDO/2 calculations with the use of a standard sp basis predict greater stability for the structures with a three-coordinate phosphorus atom, in contradiction to experiment.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 486–490, July–August, 1989.In conclusion, we express our thanks to V. L. Foss for showing an interest in this work and for some valuable discussions.     

Quantum-chemical investigation of the complex of Mg-porphin with tetracyanoquinodimethane

The potential hypersurface for the interaction of the molecules of Mg-porphin (P) and tetracyanoquinodimethane (TCQ) was investigated by the CNDO/2 method. The calculated energy minimum amounts to –8.95 eV and corresponds to a distance of 2.1 Å between the planes of the molecules with some displacement in relation to the central mutual arrangement. The results are regarded as tentative in view of the fact that the CNDO/2 method exaggerates the interaction. The electronic spectra of the P·TCQ complex are calculated by the CNDO/S-CI method for a series of arrangements of P and TCQ. Satisfactory agreement with experiment is obtained with a distance of about 3 Å between the planes of the molecules. It was shown that there are two transitions with charge transfer in the near IR region of the spectrum and also several transitions of the same type in the visible and near UV regions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 431–437, July–August, 1990.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

The results of calculations by the Pariser-Parr-Pople method and the expanded Hückel method of oligomeric compounds and fragments from which aromatic polyimide macromolecules are constructed are presented and discussed. In connection with the controversial character of the problem of the structures of the intermediates in the destruction of polyimides and the use, in this case, of the concept of imide-isoimide rearrangement, the relative advantageousness of the tautomeric forms of imides is evaluated, the participation of the imide ring in one or another form in conjugation is discussed, the spectral differences in the forms are established, etc. The strength characteristics of the bonds in polyimides were estimated in connection with the possibility of homolytic and hydrolytic cleavage of polyimides at these bonds.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.8, pp. 1048–1056, August, 1972.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

The characteristics of the electronic structures of a number of model aromatic oxazoles realized in aromatic polyoxazoles were obtained within the framework of the Pariser-Parr-Pople method. The UV spectra of most of them were interpreted. The stereoisomerism of dibenzoxazoles is examined.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Indigo and its dimer, trimer, dehydro, and leuco forms were investigated within the framework of the Pariser-Parr-Pople method. The electronic structures of the compounds in the ground and excited states and the effect of chain lengthening are discussed, and the UV absorption spectra are interpreted. Several characteristics of the chromaticity of the investigated compounds as representatives of vat dyes are examined. The estimated (from calculations) energetic favorability of the indigoid, dehydro, and leuco forms of indigo is used in discussing the observed and experimental ease of redox transformations of indigo.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 794–798, June, 1972.     

An investigation of lithium intercalation into the carbon nanotubes by a.c. impedance

The closed and open carbon nanotube electrodes have been studied as a function of frequency and the open circuit cell potential. A comparison of these spectra reveals different behaviors depending on the form of the carbon nanotubes: for the closed carbon nanotubes the impedance spectra consists of only one arc in the high frequency, for the open carbon nanotubes the impedance spectra consists of two separated semicircles in the high frequency. Analysis based on plausible equivalent circuit models for the carbon nanotubes lead to evaluation the kinetic parameters for the various physicochemical processes occurring at the electrode/electrolyte interface.     

Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Those structures of aromatic imidazoles that can be realized in polybenzimidazoles were investigated within the framework of the computational scheme of the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were exposed. A judgment is expressed relative to the strength characteristics of the bonds in the imidazole rings during thermal or thermal oxidative destruction of aromatic polybenzimidazoles. The stereoisomerism of dibenzimidazoles was examined. The UV absorption spectra of the investigated compounds were interpreted.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 10, pp. 1396–1402, October, 1973.     

Quantum-chemical investigation of the mechanism of the sulfonation of pyrrole

A detailed quantum-chemical study of the sulfonation of pyrrole with regard to the effect of the solvent (the model of overlapping spheres) on the energy characteristics of the formation of the σ-complexes produced during attack on the α-and β-positions of the heterocycle and their possible transformation paths was made by density functional theory [the B3LYP/6-31G(d) method]. The possibility of mutual transformations between the isomeric σ-complexes by α/β-migration of the SO₃ is examined. The formation of pyrrolesulfonic acids was studied for the case of the intramolecular rearrangement of the complexes. Comparison of the activation energies shows that in contrast to the gas-phase reaction the formation of the β-sulfonic acid is preferred in methylene chloride: the solvation energy of the α-isomer of the σ-complex is higher than the energy for the transition state of its rearrangement and its product, α-pyrrolesulfonic acid, leading to an increase in the kinetic barrier and to a decrease of the energy gain on the path to the formation of the latter. The opposite variation of the energy characteristics on the path to the β-isomer with regard to solvation leads to agreement between the calculated data and the experimentally observed preferred formation of the β-pyrrolesulfonic acid. Dedicated to Mikhail Grigor’evich Voronkov. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1647–1654, November, 2006.     

Quantum-chemical investigation of the triplet-triplet absorption in photochromic indolinespiropyrans

The triplet-triplet absorption spectra of the initial and photoinduced forms of unsubstituted and methoxy- and nitro-substituted indolinespiropyrans were calculated by the CNDO/S method. An interpretation of the experimental data with respect to the absorption of indolinespiropyrans in the visible region is proposed on the basis of the results. The presence of long-wave triplet-triplet absorption in the spectral region > 800 nm is indicated. A suggestion is made about the nature of the kinetic changes in the absorption spectra of nitro-substituted indolinespiropyrans during the photochromic transformations. An explanation of the nature, the structure, and the complexity of the kinetics of decay of the absorption band in the region of 400–460 nm is given in terms of the cis-isomeric form, which is formed immediately after photoexcitation of the indolinespiropyran. The nature of the triplet-triplet absorption of the trans isomers of the colored form was established. An analysis is made of the orbital nature of the triplet states of the initial and photoinduced forms of unsubstituted and methoxy- and nitrosubstituted indolinespiropyrans.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 24, No. 3, pp. 291–299, May–June, 1988.The authors express their gratitude to G. G. Konoplev for taking part in the discussion of the results.     

Quantum-chemical investigation of the electrophile affinity of molecules of five-membered heterocycles with one hetero-atom and some model systems

Quantum-chemical calculations have been made of the energy characteristics of the molecules of pyrrole, furan, thiophene, and selenophene, the simplest derivatives of N, O, S, and Se with sp³-and sp²-hybridized C atoms and heteroatoms, and also of the products of addition of proton and certain other electrophiles to these molecules. The calculations were carried out by HF, B3LYP, and MP2 methods with the 6−31+G(d) basis set with corrections to the energy of zero-point vibrations. It was shown that the values of the affinity of the nitrogen-containing systems towards the electrophile were significantly greater than for their analogs, derivatives of chalcogens, while the relative stability of the onium states of the latter depends both on the hybridization of the heteroatoms, and also on the nature of the electrophile. Analysis of the obtained results made it possible to build a stability series of the onium compounds and to interpret the special features of the positional selectivity in electrophilic substitution reactions of five-membered heteroaromatic compounds with one heteroatom. Dedicated to the remarkable heterocyclic chemist Aleksandr Fedorovich Pozharskii on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1645–1654, November, 2008.     

Quantum-chemical investigation of the mechanism of ionic polymerization in crystals

The results of quantum-chemical investigations of radiation-induced polymerization in molecular crystals are presented. The detailed calculations of the potentials energy curves characterizing the chain generation and propagation reactions, with explicit account of the reacting system interaction with the crystalline environment, provide a reasonable interpretation of the experimental observations. The basic conclusion is that the addition of the growing polymer ion to the monomer molecule placed at a lattice point needs no activation energy. The polymer chain is spontaneously moving in the interlayer space of the crystalline lattice at every propagation step, the overall displacement reaching a macroscopic value. Several termination mechanisms are briefly discussed. The possibility of molecular tunneling cannot be completely eliminated, however, it is expected to occur at the nonchemical preliminary stage of the reaction.     

Quantum-chemical investigation of phosphoryl halides and thiophosphoryl halides

Theoretical and Experimental Chemistry -