Study of the formation of polyimide from complexes of benzophenonetetracarboxylic acid diester with different diamines. 3. Dielectric study of thermal imidization

Dielectric loss peaks caused by thermal imidization were observed for the three complexes of benzophenonetetracarboxylic acid dimethyl ester (BZPE) with different diamines. The mechanism of the formation of imide rings from complexes with hydrogen bonds and with separated charges was specified. The specific features of thermal imidization of the BZPE·diaminopyridine dimeric complex were confirmed and it was shown that heat treatment of the complex of BZPE with hexamethylenediamine yields a softening polyimide and thermal imidization takes place at lower temperatures.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 534–539, March, 1990.     

Investigation of the process of polyimide formation from complexes of the diester of benzophenonetetracarboxylic acid with diamines

The kinetics of thermal imidization of the H-complexes derived from the diethyl ester of 3,3,4,4-benzophenonetetracarboxylic acid (EBZP) and various diamines have been studied. A comparison of kinetic parameters obtained for the imidization of H-complexes based on ethyl or methyl esters of this acid has disclosed the differences in the behavior of each of the two H-bonds and the contribution of each bond to the mechanism of polyimide formation from the respective H-complexes.For part 5, see ref.¹ Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 300–303, February, 1993.     

Investigation of process of polyimide formation from complexes of diester of benzophenonetetracarboxylic acid with diamines. 1. Investigation of thermal imidization by means of IR spectroscopy

The thermal imidization of complexes of benzophenonetetracarboxylic acid diester with diamines is greatly different from the thermal imidization of the corresponding mechanical mixtures. Preliminary complexation gives a considerably greater degree of completion of the imidization. It is concluded that diffusion processes play a decisive role in the solid-phase thermal imidization of the complexes. On the basis of similar values of the free energy of activation at identical temperatures for complexes with different diamines, it is concluded that the reactivity of the functional groups has little influence on the kinetics of solid-phase imidization of the complex. Alternative schemes are proposed for the formation of polyimides from the complexes, leading to an intermediate mixed-unit prepolymer with amido acid, amido ester, and imide units in the chain.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2462–2468, November, 1989.The authors wish to thank V. V. Shamanin for discussion of the results.     

Investigation of polyimide formation from the complexes of the diester of benzophenonetetracarboxylic acid with diamines 7. Role of theo-carboxylic group of acid diester in the formation and imidization of H-complexes

The kinetics of thermal imidization of various H-complexes of semiesters of bis(o-phthalic) acids with diamines was studied. The activation energy of the imidization was shown to increase with increasing pK_a value of the diamine andE _a value of the dianhydride and with decreasing nucleophilicity of the alcohol used for the synthesis of H-complexes. The experimental kinetic data and the results of quantum chemical calculations of the heats of formation of the initial H-complexes and transition states made it possible to propose a mechanism for the imidization reaction. This mechanism takes into account the catalytic effect of the carboxylic group of the semiester in theo-position with respect to the ester group.For report 6, seeIzv. Akad. Nauk, Ser. Khim., 1993, 300 [Russ. Chem. Bull., 1993,42, 255 (Engl. Transl.)].Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1060–1065, June, 1995.     

The role of the pyrimidine ring in the main chain of polyamic acids and polyimides

Thermoimidization kinetics of polypyromellitamic acids prepared from 2,5-bis(p-aminophenyl)pyrimidine and 4,4-diaminoterphenyl have been investigated by IR spectroscopy. It has been shown that the activation energy for the pyrimidine-containing polymer is nearly twice as low as that for the aromatic analog. This is explained by base catalysis of cyclization of the amidoacid fragments by pyrimidine rings in polymer chains. Base catalysis facilitates the process of imidization and favors the formation of polyimidic macromolecules with a lower incidence of defects. Also, the pyrimidine rings obviously catalyze the resynthesis of amidoacid fragments from the anhydride rings and amino groups formed on the destruction of the polymer chain during thermoimidization, and ensure almost complete recovery of the macromolecules with the previous bonds.For part 3, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 429–432, March, 1994.The authors are grateful to T. K. Meleshko for consultations about chemical imidization.     

Crystal and Molecular Structure of 5-Acetylamino-3-nitro-1,2,4-triazole

This paper reports on an X-ray diffraction study of 5-acetylamino-3-nitro-1,2,4-triazole. Monoclinic crystals, space group P2_1/c; a=8.2079(7), b=13.096(1), c=13.650(1) , =100.64(1)°. Two independent molecules are identical in conformation and both have an N–H···sO intramolecular hydrogen bond; the difference lies in their interactions with neighbors. In molecule A, the acetyl oxygen atom and all nitrogen atoms (except those of the amino group) are involved in the intermolecular hydrogen bonds; in molecule B, these hydrogen bonds are formed by only two NH groups in addition to the above oxygen. The crystal structure of the title compound is compared with that of 5-amino-3-nitro-1,2,4-triazole.     

Cocrystals of U-shaped ureadicarboxylic acid with 2-aminopyrimidine and melamine: rhombus-shaped cyclic heterotetramer motifs

Single crystal X-ray structures of cocrystals, 1·2 and 1·3, derived from U-shaped ureadicarboxylic acid (1) with 2-aminopyrimidine (2) and melamine (3), respectively, were examined. Cocrystals were obtained as a 1:1 mixture of 1 and the corresponding base. Two molecules of 1 and two molecules of the base were combined together via intermolecular H-bonding creating a supramolecularly assembled cyclic heterotetramer motif of rhombus shape. In the case of cocrystal 1·3, the cyclic heterotetramers were connected via H-bonding by utilizing a remaining amino group of melamine resulting in the formation of a tape of cyclic heterotetramer.     

Stereochemistry of nitrogen heterocycles. 62. Conformational analysis of isomers of 2-methyl-cis-decahydro-5-quinolinol

Isomers of 2-methyl- and 1,2-dimethyl-cis-decahydro-5-quinolinol with a syn orientation of the hydroxy and amino groups and different orientations of the methyl group relative to the methylene group at C₍₈₎H₂ were subjected to conformational analysis. In the case of a cis orientation of the methyl and methylene groups the equilibrium is shifted completely to favor the conformation with an intramolecular hydrogen bond, whereas in the case of their trans orientation the mole fraction of this conformation amounts to 21–24% for the secondary amino alcohol and 18–21% for the tertiary amino alcohol. The energies of the hydrogen bonds were determined from the intensities of the absorption bands of the free and associated hydroxy groups in the IR spectra: for the secondary hydroxy amine, according to the band of the free hydroxy group, G⁰ _OH/N is –0.8 kcal/mole, whereas, according to the band of the associated hydroxy group, it is –0.9 kcal/mole; the values for the tertiary hydroxy amine are, respectively, –0.7 and –0.8 kcal/mole.See [1] for Communication 61.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1514–1519, November, 1987.     

Spatial and Electronic Structure of 2-(2-Furyl)- and 2-(2-Thienyl)pyrroles According to 1H and 13C NMR Data

In 2-(2-furyl)- and 2-(2-thienyl)pyrroles the heterocycles are in efficient ,-conjugation. The presumably possible for this compounds intramolecular hydrogen bond N-H···O or N-H···S is lacking. The COCF₃ group in position 2 of the pyrrole ring is syn-oriented with respect to pyrrole fragment, and the orientation is fixed by an intramolecular hydrogen bond N-H···O. However no bifurcating hydrogen bonds arise in the molecules containing COCF₃ group.     

Complex formation reactions of palladium(II)-1,3-diaminopropane with various biologically relevant ligands. Kinetics of hydrolysis of glycine methyl ester through complex formation

The interaction of [Pd(DAP)(H₂O)₂]²⁺ (DAP = 1,3-diaminopropane) with some selected bio-relevant ligands, containing different functional groups, were investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA constituents. Stoichiometry and stability constants of the complexes formed are reported at 25°C and 0.1 M ionic strength. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants is examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. DNA constituents form 1:1 and 1:2 complexes. The effect of dioxane on the acid dissociation constants of CBDCA and the formation constant of its complex with Pd(DAP)²⁺ was reported. The kinetics of hydrolysis of glycine methyl ester bound to [Pd(DAP)(H₂O)₂]²⁺ was studied at 25°C and 0.1M ionic strength.      

Transfer Reactions of Rydberg (Quasi-Rydberg Molecular) Electrons in Condensed Media: IV. Large Proton Displacements upon Phosphorescence Quenching via Highly Excited Triplet States T* of Substituted Aromatic Solute Molecules in Solutions at 77 K

Intramolecular phosphorescence quenching via states T* in aromatic solute molecules containing N–H (diphenylamine (DPA) or carbazole), O–H (naphthol), etc. bonds was observed in methylcyclohexane at 77 K. The quantum yield of quenching measured for DPA increases with increasing the energy of the T* state. As in the case of external electron acceptors, the quenching and photodissociation are associated with the capture of excited * electrons onto polarized bonds N–H⁺, O–H⁺and with the formation of triplet complexes (for example, Ph₂N···H*, where H* is the excited hydrogen atom). The complexes can be deactivated via configurations with large proton displacement distances (Ph₂N^–···H⁺).     

Synthesis and Inclusion Properties of the Host Compound 1,3-Dihydro-1,1,3,3-tetraphenylisobenzofuran. X-Ray Crystal Structures of the Free Host and of an Inclusion Compound with 1,4-Dioxane

A novel host molecule, 1, suitable for crystalline lattice-type inclusion, has been synthesized, and its cocrystal formation ability has been investigated. Host 1 proved to be of potential use for organic solvent separation and retrieval, and a promising auxiliary for solidification of certain odorous substances. The crystal structures of the solvent-free host 1, and its complex with 1,4-dioxane (1 : 1), have been determined by single crystal X-ray diffraction. The structure of 1 (guest-free) is triclinic, P , with a = 9.452(2), b = 10.359(3), c = 13.116(3) Å, = 101.80(2), = 106.53(1) and = 104.32(1)°. The spacious, propeller-like molecules are held together by weak van der Waals' forces. The dioxane inclusion compound is monoclinic, P21/a, with a = 15.050(1), b = 8.641(1) and c = 20.658(1) Å, and = 94.56(1)°, and contains two crystallographically independent guest molecules, both located around symmetry centres. The molecular packing seems to be governed by C—H···O type bonds (C···O = 3.31 and 3.48 Å) from the host to the dioxane oxygens.     

The coordination chemistry of 2,2′-oxydibenzoic acid, 2,2′-thiobenzoic acid, 3,3′-oxydipropionic acid and 3,3′-thiodipropionic acid with selected first row transition metal ions

Summary Solid metal complexes of the title ligands are described. The largest range is prepared with 2,2-oxydibenzoic acid, namely Zn^IIL · 1.5 H₂O, Cu^IIL · H₂O, Co^IIL · H₂O, Fe^IIIL · (OH) and Fe^IIIL · (OH) · H₂O where L denotes the ligand dianion. Zinc(II) and copper(II) complexes of the other ligands are prepared for comparison and these have, generally, the stoichiometry ML · xH₂O (0.5 x 1.5; M = Cu or Zn).The i.r. spectra are discussed and antiferromagnetic behaviour is noted for the copper(II) and iron(III) complexes. Magnetic properties are investigated over the 80–300 K range in several cases. Reflectance (u.v./visible) spectroscopy and Mössbauer spectroscopy have been used, where appropriate, in association with the magnetic data and i.r. data to suggest that the metal is located in a distorted MO₆ environment involving unsymmetrically bidentate carboxylate groups and -aquo or -hydroxo groups.     

Reactivity of Cyclohexanol CH Bonds toward the tert-Butylperoxy Radical

The effect of the hydroxy group on the partial rate constants of the reactions of the tert-butylperoxy radical with CH bonds in cyclohexanol at 333 K was studied by the Howard–Ingold method. The overall reaction rate constant increased with decreasing alcohol concentration in chlorobenzene because of complex effects of hydrogen bonds at the steps of chain growth and termination. The hydroxy group activates the -CH bond and deactivates the - and -CH bonds. The reactivity of -CH bonds is close to the reactivity of CH bonds in cyclohexane.     

Polyimides from complexes of benzophenonetetracarboxylic acid diesters with diamines. 5. Mechanism of thermal cyclization of H-complexes

The results of a study, by thermal mass spectrometric analysis and NMR spectroscopy, of the polycondensation of H-complexes are presented from which it is possible to propose a mechanism for the reaction. It is shown that conversion of the H-complexes into polyimides takes place through the formation of intermediate zwitterions with an amino acid bond after initial separation of methanol, following which elimination of water commences in one stage to form an imide ring. The role of theortho position of the functional groups in the acid ester during the formation of the hydrogen bond is discussed.Institute of Macromolecular Compounds, Russian Academy of Sciences, 199004 St. Petersburg. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2517–2524, November, 1992.     

The determination of enthalpies of formation of organic free radicals from bond dissociation energies. 5. Organosulfur radicals

The formation enthalpies (H _f°) of 12 organosulfur radicals (R^·) were determined for the first time from the published values of dissociation energies of R—X bonds.     

Mutual Weakening of Hydrogen Bonds Formed by a Water Molecule with Two Proton Donors

Based on results of ab initio (6–31G and ECP) calculations, new data on the mutual effect of hydrogen bonds in (HHal)_n · H₂O · ((CH₃)₂O)_m (n = 0, 1, 2; m = 0, 1, 2) aquacomplexes have been obtained. It is shown that the Hbonds formed by the lone electrons of the oxygen atom of the water molecule (by 20%) weaken each other significantly. The enthalpy of formation of HOH...O(CH₃)₂ bonds depends on which and how many halogen hydride molecules are bound with the water molecule via its lone electrons. But the ratio of the strengths of the HOH...O(CH₃)₂ bonds formed by the fragment (HHal)_n · H₂O (n = 0, 1, 2) with one and with two molecules of dimethyl ether remains virtually constant ( 10%).     

Peptides of sarcolysin with γ-aminobutyric acid

Conclusions Peptides of sarcolysin with-aminobutyric acid have been synthesized, containing N-terminal and C-terminal sarcolysin, as well as a free and a formylated amino group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 161–162, January, 1970.     

Aluminum Complexes with a Donor Polymer: New Route to Organic/Inorganic Polymer Hybrids

The formation of alumina particles from aluminum salts in the presence of poly(1-vinylimidazole) was investigated by quantitative ²⁷Al NMR, potentiometry and FTIR spectra. The interaction of poly(1-vinylimidazole) with aluminum chloride and nitrate in an aqueous medium stabilizes [AlO₄Al₁₂(OH)₂₄]⁷⁺ and less ordered polymeric particles. The addition of NaOH (NaOH: Al 2) results in water-insoluble organic/inorganic hydrogen-bonded composites. Stabilization of the complexes is realized by cooperative hydrogen N···H—O—Al bonds, without N Al donor-acceptor interactions.     

Syntheses and crystal structures of bis(4-dimethylaminopyridine) group 12 trifluoroacetates — M(OCOCF3)2·2DMAP (M=Zn, Cd, Hg)

Bis(4-dimethylaminopyridine) group 12 trifluoroacetates—M(OCOCF₃)₂·2DMAP (M=Zn, Cd, Hg) were prepared in quantitative yields from the anhydrous metal trifluoroacetates and DMAP. All compounds crystallize in the triclinic space group (no. 2) with two molecules per unit cell. While Zn(OCOCF₃)₂·2DMAP is built up by well-separated tetrahedral units exhibiting strongly covalent ZnO bonds to monodentate trifluoroactate groups, Cd(OCOCF₃)₂·2DMAP and Hg(OCOCF₃)₂·2DMAP form dimeric units. The metal centers are distorted octahedrally surrounded by two axial DMAP ligands, two ionic bridging and one chelating trifluoroacetate group.