International Journal of Molecular Sciences

333 KiB

Open AccessArticle

Quantitative Structure–Property Relationships for Aryldiazonia

by Alexei N. Pankratov and Oxana I. Zhelezko

Int. J. Mol. Sci. 2002, 3(7), 822-855; https://doi.org/10.3390/i3070822 - 31 Jul 2002

Cited by 7 | Viewed by 7517

By the fact of finding 43 relationships, we have shown that the reduction potentials, dimerization potentials and potentials in half-equivalent point on titration of aryldiazonium cations XC₆H₄N⁺≡N (chemical reduction with K₄[Fe(CN)₆] and TiCl [...] Read more.

By the fact of finding 43 relationships, we have shown that the reduction potentials, dimerization potentials and potentials in half-equivalent point on titration of aryldiazonium cations XC₆H₄N⁺≡N (chemical reduction with K₄[Fe(CN)₆] and TiCl₃ in water, (C₂H₅)₃N, (í-C₄H₉)₄N⁺−OH, CH₃OK and C₁₀H₈^•−Na⁺ in acetone; polarographic reduction in nitromethane, sulfolane, and N,N-dimethylformamide) are related linearly to the quantum chemically evaluated electron affinities (A) and to the stabilization energies of radicals formed on diazonium cations reduction. Sixty six linear correlations of frequencies (ν) characterizing a collection of bonds stretching vibrations of the C-N⁺≡N fragment in the XC₆H₄N⁺≡NY⁻ salts with different anions in vaseline oil, N,N-dimethylformamide, acetone, ethylacetate, methanol, water, with the bonds orders of N≡N and C-N, with the charges on carbon atoms in para positions of the C₆H₅X molecules aromatic rings, with the mesomeric dipole moments (μ_m) of X substituents have been found. Twelve quantitative relationships combining the μ_m and ν quantities with the A values have been established. The interrelations obtained have an explicitly expressed physical meaning, are featured by rather high correlation coefficients and have a predictive power in respect to redox properties, electron affinities, vibrational frequencies of aryldiazonia, as well as to mesomeric dipole moments of atomic groups in organic molecules. Full article

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60 KiB

Open AccessArticle

Among Synthetic, Supramolecular and Theoretical Chemistry Stabilization of Short-lived Species in “Molecular’ or ‘Supramolecular Flasks’

by Helena Dodziuk

Int. J. Mol. Sci. 2002, 3(7), 814-821; https://doi.org/10.3390/i3070814 - 31 Jul 2002

Cited by 8 | Viewed by 6255

Abstract

The recent advances in the syntheses of short-lived species inside cages of ‘molecular’ or ‘supramolecular flasks’ lead their more involved studies. Moreover, they open prospects for much closer and fruitful cooperation among organic synthetic, theoretical and supramolecular chemists that will allow one to [...] Read more.

The recent advances in the syntheses of short-lived species inside cages of ‘molecular’ or ‘supramolecular flasks’ lead their more involved studies. Moreover, they open prospects for much closer and fruitful cooperation among organic synthetic, theoretical and supramolecular chemists that will allow one to obtain and study numerous, exciting highly strained molecules, ions and/or radicals. Full article

413 KiB

Open AccessArticle

Reduction of Nitroaromatic Compounds on the Surface of Metallic Iron: Quantum Chemical Study

by Igor Zilberberg, Alexander Pelmenschikov, Christian J. Mcgrath, William Davis, Danuta Leszczynska and Jerzy Leszczynski

Int. J. Mol. Sci. 2002, 3(7), 801-813; https://doi.org/10.3390/i3070801 - 31 Jul 2002

Cited by 14 | Viewed by 9138

Abstract

The initial reduction steps of nitroaromatic compounds on the surface of metallic iron have been studied theoretically using nitrobenzene (NB) as a representative of nitroaromatic compounds. The quantum chemical cluster approximation within the semiempirical Neglect of Diatomic Differential Overlap for Metal Compounds method [...] Read more.

The initial reduction steps of nitroaromatic compounds on the surface of metallic iron have been studied theoretically using nitrobenzene (NB) as a representative of nitroaromatic compounds. The quantum chemical cluster approximation within the semiempirical Neglect of Diatomic Differential Overlap for Metal Compounds method was applied to model the Fe(110) crystallographic surface, taken as a representative reactive surface for granular iron. This surface was modeled as a 39-atom two-layer metal cluster with rigid geometry. The associative and dissociative adsorption of nitrobenzene was considered. Based on our quantum chemical analysis, we suggest that the direct electron donation from the metal surface into the π* orbital of NB is a decisive factor responsible for subsequent transformation of the nitro group. Molecularly adsorbed NB interacts with metal iron exclusively through nitro moiety oxygens which occupy tri-coordinated positions on surface The charge transfer from metal to NB of approximately 2 atomic units destablizes the nitro group. As a result, the first dissociation of the N-O bond goes through a relatively low activation barrier. The adsorbed nitrosobenzene is predicted to be a stable surface species, though still quiet labile. Full article

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115 KiB

Open AccessArticle

A Protons Exchanged Montmorillonite Clay as an Efficient Catalyst for the Reaction of Isobutylene Polymerization

by Amine Harrane, Rachid Meghabar and Mohammed Belbachir

Int. J. Mol. Sci. 2002, 3(7), 790-800; https://doi.org/10.3390/i3070790 - 31 Jul 2002

Cited by 47 | Viewed by 11025

Abstract

“Maghnite” a montmorillonite sheet silicate clay, exchanged with protons to produce “H-Maghnite” is an efficient catalyst for cationic polymerization of many vinylic and heterocyclic monomers (Belbachir, M. U.S. Patent. 066969.0101 –2001). The structure compositions of both “Maghnite” and “H-Maghnite” have been developed. Isobutylene [...] Read more.

“Maghnite” a montmorillonite sheet silicate clay, exchanged with protons to produce “H-Maghnite” is an efficient catalyst for cationic polymerization of many vinylic and heterocyclic monomers (Belbachir, M. U.S. Patent. 066969.0101 –2001). The structure compositions of both “Maghnite” and “H-Maghnite” have been developed. Isobutylene monomer, wich is polymerizable only by cationic process (Odian,G. La Polymerisation :principes et Applications; Ed.Technica: New York, 1994; pp 222-226), was used to elucidate the cationic character of polymerization. The polymerization was performed under suitable conditions at isobutylene vaporization temperature (–7°C). Experiments revealed that polymerization induced by “H-Maghnite” proceed in bulk and in solution. In contrast to findings with methylene chloride CH₂Cl₂ as a polar solvent, polymerization yields with hexane C₆H₁₄ non-polar solvent is very significant. In bulk polymerization, Isobutylene conversion increases with increasing “H-Maghnite” proportion. Full article

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127 KiB

Open AccessArticle

Post Hartree–Fock and DFT Studies on Pyrrole···Nitrogen and Pyrrole···Carbon Monoxide Molecules

by R. Kanakaraju and P. Kolandaivel

Int. J. Mol. Sci. 2002, 3(7), 777-789; https://doi.org/10.3390/i3070777 - 31 Jul 2002

Cited by 13 | Viewed by 9782

Abstract

The hydrogen bonded and van der Waals isomers of pyrrole···nitrogen and pyrrole···carbon monoxide have been studied using ab initio and density functional theory methods. Complex geometries and total energies of the isomers have been determined at HF, MP2, B3LYP and B3PW91 levels of [...] Read more.

The hydrogen bonded and van der Waals isomers of pyrrole···nitrogen and pyrrole···carbon monoxide have been studied using ab initio and density functional theory methods. Complex geometries and total energies of the isomers have been determined at HF, MP2, B3LYP and B3PW91 levels of theory employing 6-31G* basis set. For pyrrole···nitrogen complex, only two isomers have stable structure and the more stable one is found to be the hydrogen bonded isomer. Among the five isomers of pyrrole···carbon monoxide complex, the hydrogen bonded isomer is found to be the most stable form. The interaction energy for all these isomers have been calculated after eliminating the basis set superposition errors by using the full counterpoise correction method. Chemical hardness, chemical potential have been calculated and are used to study the stability of the molecules. Full article

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57 KiB

Open AccessArticle

Reverse Phase Thin Layer Chromatography of Aminoalkanethiosulfuric Acids, Mercaptoalkanamines and Aminoalkyl Disulfides

by Maria Das Graças Cardoso, David Lee Nelson, Antônia Tavares do Amaral, Custódio Donizete Dos Santos, Alcilene De Abreu Pereira and Ana Cláudia Barneche De Oliveira

Int. J. Mol. Sci. 2002, 3(7), 755-763; https://doi.org/10.3390/i3070755 - 31 Jul 2002

Cited by 3 | Viewed by 8759

Abstract

The experimental Rm values for a series of aminoalkanethiosulfuric acids, mercaptoalkanamines and aminoalkyl disulfides were determined by reverse phase thin layer chromatography. The Rm values were determined for various concentrations of methanol: water and the correlation obtained was extrapolated to 100% water. These [...] Read more.

The experimental Rm values for a series of aminoalkanethiosulfuric acids, mercaptoalkanamines and aminoalkyl disulfides were determined by reverse phase thin layer chromatography. The Rm values were determined for various concentrations of methanol: water and the correlation obtained was extrapolated to 100% water. These values permitted the calculation of the log P values for each substance. The log P values obtained by this method were compared with those obtained using the shake-flask method and by theoretical calculations utilizing fragment constants. Full article

103 KiB

Open AccessArticle

Quantum Chemical and FTIR Spectroscopic Studies on the Linkage Isomerism of Carbon Monoxide in Alkali-Metal-Exchanged Zeolites: A Review of Current Research

by C. Otero Areán, G. Turnes Palomino, A. A. Tsyganenko and E. Garrone

Int. J. Mol. Sci. 2002, 3(7), 764-776; https://doi.org/10.3390/i3070764 - 30 Jul 2002

Cited by 28 | Viewed by 10919

Abstract

When adsorbed (at a low temperature) on alkali-metal-exchanged zeolites, CO forms both M(CO)⁺ and M(OC)⁺ carbonyl species with the extra-framework alkali-metal cation of the zeolite. Both quantum chemical and experimental results show that C-bondend adducts are characterized by a C−O stretching [...] Read more.

When adsorbed (at a low temperature) on alkali-metal-exchanged zeolites, CO forms both M(CO)⁺ and M(OC)⁺ carbonyl species with the extra-framework alkali-metal cation of the zeolite. Both quantum chemical and experimental results show that C-bondend adducts are characterized by a C−O stretching IR band at a frequency higher than that of 2143 cm^-1 for free CO, while for O-bonded adducts this IR band appears below 2143 cm^-1. The cation-CO interaction energy is higher for M(CO)⁺ than for M(OC)⁺ carbonyls, although the corresponding difference decreases substantially when going from Li⁺ to Cs⁺. By means of variable-temperature FTIR spectroscopy, this energy difference was determined for several alkali-metal cations, and the existence of a thermal equilibrium between M(CO)⁺ and M(OC)⁺ species was established. The current state of research in this field is reviewed here, with a view to gain more insight into the thermal isomerization process. Full article

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Int. J. Mol. Sci., Volume 3, Issue 7 (July 2002) – 7 articles , Pages 755-855

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