Synthesis,characterization, and non-isothermal curing kinetics of two silicon-containing arylacetylenic monomers

Vinyltri(phenylethynyl)silane ((ph–C≡C)₃–Si–C=CH₂; VTPES) and phenyltri(phenylethynyl)silane ((ph–C≡C)₃–Si–ph; PTPES) were synthesized by Grignard reaction. Their molecular structures were characterized by means of ¹H NMR, ¹³C NMR, ²⁹Si NMR, and FT-IR spectroscopy. Their nonisothermal thermal curing processes were characterized by DSC, and the corresponding kinetic data, for example activation energy (E), pre-exponential factor (A), and the order of the reaction (n), were obtained by the Kissinger method. The results showed that the melting points of VTPES and PTPES were 84 and 116 °C, respectively. Their curing reaction rates were consistent with first-order kinetic equations. VTPES monomer had a lower activation energy and curing temperature as a result of coordination between reactive groups.     

13C and19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates. A method of signal assignment based on the carbon—fluorine spin-spin coupling constants

The¹³C and¹⁹F NMR spectra ofZ- andE-isomers of β-X-substituted α,β-difluorostyrenes (X=F, Cl, CpFe(CO)₂, Re(CO)₅, Re₂(CO)₉Na) were studied. Direct and long-range (across 1–5 bonds) spin-spin coupling constants and the (¹³C−¹²C) isotope shifts in the¹⁹F NMR spectra were determined. The study of the¹³C satellites in the¹⁹F NMR spectra of substituted difluorostyrenes permitted assignment of the¹³C NMR signals of the vinylic carbon atoms. Similarly, the signals in¹⁹F NMR spectra were assigned based on coupling constants of fluorine withipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X=F, Cl). The developed approach was applied to the elucidation of the structure ofZ−PhCF=CClFe(CO)₂Cp. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya. No. 8, pp. 1575–1579, August, 1998.     

Synthesis and high-resolution NMR spectra of A-nor-derivatives of 11-deoxyglycyrrhetic acid

Several skeletal and oxidative transformations of 11-deoxyglycyrrhetic acid were carried out to produce A-nor-derivatives. Signals for protons and C atoms in the PMR and ¹³C NMR spectra of the A-nor-derivatives were assigned using high-resolution ¹H (400 MHz) and ¹³C (125 MHz) NMR spectroscopy. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 445–448, September–October, 2006.     

Spectroscopic and structural study of the ambazone hydrochloride

Ambazone, a well-known antimicrobial compound, presents also oncostatic properties. The solid form, obtained by using solvent-drop grinding procedure, was characterized by using several physical techniques such as FTIR, X-ray photoelectron spectroscopy, ¹³C NMR and ¹⁵N NMR spectroscopies, thermal analysis, X-ray powder diffraction and mass spectrometry. Based on these data, it was demonstrated that an ambazone–hydrochloride was obtained: new vibrations corresponding to NH₂ ⁺ were identified. DTA–TG–DSC and MS data revealed that a new crystal type has been obtained. X-ray diffraction data allowed the determination of the lattice parameters and the most probable space group P _21/c was established also with only one molecule per asymmetric unit.     

Synthesis,spectroscopic and configurational study,and ab initio calculations of new diazaphospholanes

New 2-substituted diazaphospholane-2-oxides (I-III, V-VIII) and diazaphosphorinane-2-oxide (IV) were synthesised and characterised by ¹H, ¹³C, and ³¹P NMR, IR spectroscopy, and elemental analysis. The presence of chiral diamino groups in compounds II and V–VIII gives rise to various diastereomers so that the ³¹P{¹H} NMR spectra demonstrated three and two peaks with different ratios, respectively. Also, the ¹H and ¹³C{¹H} NMR spectra of compounds II and V–VIII revealed three and two sets of signals for the related conformers (diastereomers). Interestingly, the ³¹P NMR spectrum of V in D₂O indicated a great upfield shift (Δδ = 19.0) for ³¹P relative to the value obtained in DMSO-d₆ (solvent effect). The two signals in V split further to three signals in the presence of β-cyclodextrin. Moreover, conformational analysis of diazaphospholane V was studied by ab initio calculations at the HF and B3LYP levels of theory using the Gaussian 98 program. Results indicated that among four suggested diastereomers (C1–C4) of V, C1 and C3 containing methyl group in the equatorial position are the most stable forms.     

Hammett constants and NMR shifts of α-acyloxy carboxamide derivatives

Geometrical structures, Hammett constants, ¹H and ¹³C chemical shift values, molecular electrostatic potential maps, and several thermodynamic parameters of α-acyloxy carboxamide derivatives (4a–o) were calculated using HF and DFT/B3LYP methods with 6-31G(d) basis set. The optimized structures were compared with analogous compound. The ¹H and ¹³C NMR shielding tensors were computed with the Gauge-Independent Atomic Orbital (GIAO) method. Comparison of the experimental ¹H and ¹³C NMR chemical shifts of 4a–o molecules with the theoretical data indicates good agreement.     

X-ray photoelectron spectra and structure of 2-(2-phenylhydrazono) acetoacetanilide

2-(2-Phenylhydrazono)acetoacetanilide, itsN-methyl derivatives, and model compounds were studied by X-ray photoelectron spectroscopy. The chemical shifts were obtained from the¹³C NMR spectra. A correlation between the calculated charges, the binding energies on N atoms, and the¹³C NMR chemical shifts was found. The analysis of the XPS data and the¹³C NMR chemical shifts led to the conclusion that crystalline 2-(2-phenylhydrazono)acetoacetanilide exists mainly in the oxo hydrazone form. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–491, March, 1999.     

Thermal behaviour of hydroxymethyl compounds as models for adhesive resins

Urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins are the most widely used wood adhesives. The first stage in resin manufacturing is the formation of methylol derivatives which polycondensation leads to building the tridimensional network. Understanding the behaviour of methylol compounds in curing provides useful information for developing appropriate resin structures. Thermal behaviour of N,N′-dihydroxymethylurea, 2- and 4-hydroxymethylphenols, urea and phenol as model compounds for UF, PF and phenol–urea–formaldehyde (PUF) resins was followed by TG-DTA method. The measurements were carried out by the labsys instrument Setaram at 30–450 °C in nitrogen flow. The characteristic signals for model compounds and for some reaction mixtures were measured by high resolution ¹³C NMR spectroscopy.     

Temperature-programmed desorption of n-hexane from hydrated HZSM-5 and NH4ZSM-5 zeolites

Temperature-programmed desorption coupled with mass spectrometer as a detector (TPD), IR and ¹³C NMR measurements are used to study the adsorption of n-hexane on hydrated HZSM-5 and NH₄ZSM-5 zeolites. The ¹³C NMR measurements show that n-hexane can access the pore structure of ZSM-5 zeolites previously saturated with water. TPD spectra of n-hexane are monitored in the temperature region 50–300°C, in the case of fully or partially hydrated samples; two-stage desorption of n-hexane is found. Simultaneous desorption of water and n-hexane in the same temperature region are found, in all investigated samples.     

Chemical constituents from the roots of <Emphasis Type="Italic">Polygonum bistorta</Emphasis>

Investigation of the roots of Polygonum bistorta L. afforded seven compounds including five triterpenoids, a coumarin, and a steroid, the structures of which were identified by EIMS, ¹H NMR, ¹³C NMR, DEPT, and HMBC experiments. All the compounds have been isolated from Polygonum genus for the first time. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 463–465, September–October, 2007.     

NMR spectra of paramagnetic complexes of 1-vinylimidazole with iron group metals

The high-resolution ¹H and ¹³C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was established in the ¹H and ¹³C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular structure of the ligand was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1430–1433, June, 2005.     

Synthesis of glycyrrhetic acid derivatives

11-Deoxyglycyrrhetinic acid (DGA) (2) was produced by Clemmensen reduction of the C-11 carbonyl of 18β-glycyrrhetic acid (GA) (1). Four derivatives of GA and DGA (3a–3d) were synthesized. Their structures were elucidated using spectral data (IR, mass, ¹H, ¹³C NMR). __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 153–155, March–April, 2008.     

Effects of different GIAO and CSGT models and basis sets on 2-aryl-1,3,4-oxadiazole derivatives

The direct molecular structure implementations of the gage-including atomic orbital (GIAO), individual gages for atoms in molecules (IGAIM) and continuous set of gage transformations (CSGT) methods for calculating nuclear magnetic shielding tensors at both the Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6-31G(d), 6-311G(d), 6-31++G(d,p), 6-311++G(d,p), and 6-311++G(df,pd) basis sets are presented. Dependence on the ¹H and ¹³C NMR chemical shifts on the choice of method and basis set have been investigated. Also, these chemical shifts of 2-aryl-1,3,4-oxadiazoles 5a–g have been performed related to dihedral angles (C4–C3–C2–O) of two conformers. The optimized molecular geometries and ¹H and ¹³C chemical shift values of 2-aryl-1,3,4-oxadiazoles 5a–g in the ground state have been obtained. The linear correlation coefficients of ¹³C NMR chemical shifts for these molecules were given. The new nuclear magnetic shielding tensors of tetramethylsilane (TMS) were calculated. The data of 2-aryl-1,3,4-oxadiazole derivatives display significant molecular structure and NMR analysis. Also, these provide the basis for future design of efficient materials having the 1,3,4-oxadiazole core.     

Synthesis and NMR spectra of tetrahydrofuran-2-13C

An original method was developed for the synthesis of THF labeled selectively with the ¹³C isotope at the α-carbon atom. The effective reduction of symmetry brought about by the insertion of the isotopic label removes the excess degeneracy of the spin systems describing the multiplet structure of the ¹H and ¹³C NMR spectra, making it possible to undertake a detailed analysis. Exact values for the ¹H–¹H spin-spin coupling constants through four bonds and also the ¹³C–¹H and ¹³C–¹³C spin-spin coupling constants involving the α-carbon atom were determined for the first time. The isotopic chemical shifts of the protons and ¹³C nuclei caused by replacement of the ¹²C nucleus by ¹³C were determined. These data can be used to construct a quantitative model of the conformational behavior of THF as a molecular system in which pseudorotation in terms of vibrations with large amplitude is realized.     

Polysaccharides of Fabaceae. VI. Galactomannans from seeds of <Emphasis Type="Italic">Astragalus alpinus</Emphasis> and <Emphasis Type="Italic">A. tibetanus</Emphasis>

Galactomannans with galactose:mannose ratios 1:1.48 and 1:1.33, [α]_D +67.9 and +76.4°, [η] 870.3 and 1337.1 mL/g, and molecular weights 999 and 1549 kDa, respectively, were isolated in 0.59 and 4.65% yields (of seed mass) from seeds of Astragalus alpinus and A. tibetanus (Fabaceae). Physicochemical methods (CrO₃ oxidation; methylation–GC/MS; IR, NMR, and ¹³C spectroscopy) found that the main polysaccharide chain consisted of 1,4-β-D-mannopyranose units substituted 67.5% (A. alpinus) and 75.2% (A. tibetanus) at the C-6 position by single α -D-galactopyranose units. The contents of mannobiose blocks Man–Man, (Gal)Man–Man/Man–Man(Gal), and (Gal)Man–Man(Gal) variously substituted with galactose were according to ¹³C NMR spectroscopy 15.9, 55.5, and 28.6% in A. alpinus galactomannan and 9.9, 42.3, and 47.8% in A. tibetanus galactomannan.     

High-Resolution <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR of Glycyrrhizic Acid and Its Esters

Resonances for protons and C atoms in the ¹H and ¹³C NMR spectra of glycyrrhizic acid and its esters were assigned using high-resolution ¹H (600 MHz) and ¹³C (150 MHz) NMR methods. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 347–350, July–August, 2005.     

Accurate assignments in PMR and <Superscript>13</Superscript>C NMR spectra of anhydrolycoctonine using 2D spectroscopy

Resonances in PMR and ¹³C NMR spectra of anhydrolycoctonine were fully assigned based on a series of 1D and 2D NMR experiments. The conformation of ring A was concluded to be a distorted boat with H-1β from a comprehensive analysis of chemical shifts, SSCC, and the NOE for two possible conformations. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 267–269, May–June, 2008.     

Triterpene glycosides ofAstragalus and their genins LVII. The structure of cyclopycnanthogenin

A new cycloartane methysteroid cyclopycnanthogenin, has been found in stems of the plantAstragalus pycnanthus Boriss. (Leguminosae). Its structure has been determined on the basis of IR, mass, and¹H and¹³C NMR spectra with the involvement of DEPT experiments and 2M¹H−¹H and¹H−¹³C chemical shift correlations [¹H−¹H COSY and¹H−¹³C (HMQC)] and also 2M NMR correlations of long-range¹H−¹³C interactions (HMBC). Cyclopycnanthogenin is 6α, 16β, 25-trihydroxy-20R, 24S-epoxycycloartane-3-one. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 515–518, July–August, 1998.     

New coumarin glucoside from <Emphasis Type="Italic">Angelica dahurica</Emphasis>

A new linear furanocoumarin glycoside named dahurin B (1) was isolated from the fresh roots and rhizomes of Angelica dahurica. The structure of the new compound was elucidated by spectral techniques including ¹H NMR, ¹³C NMR, as well as HSQC, HMBC, and COSY. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 330–331, July–August, 2007.     

13C and1H NMR spectra of substituted dihydropyrroles prepared by the reaction of 2-aminooxazoles and maleimide

Substituted dihydropyrroles were characterized by¹³C and¹H NMR spectra. The spectral patterns of these compounds and reversible hydrogen—deuterium exchange are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 697–700, April, 2000.