共查询到20条相似文献,搜索用时 15 毫秒
1.
A. V. Afonin 《Russian Journal of Organic Chemistry》2010,46(9):1313-1316
The analysis of long-range spin-spin coupling 19F-1H and the other conformation-dependent parameters of 1H NMR spectra shows that aryl vinyl selenides like aryl vinyl sulfides exist as mixtures of s-cis and s-trans rotational isomers. The combined data of 1H and 13C NMR spectra reveal the increase in the torsional angle ϑ at the bond X-CH=CH2 (X = S, Se) in selenides compared to sulfides due to diminished interaction energy of the unshared electron pairs of selenium
with the π*-orbitals of the double bond as compared to analogous interaction in sulfides. 相似文献
2.
A. V. Afonin 《Russian Journal of Organic Chemistry》2011,47(4):496-499
According to the 1H and 13C NMR data and quantum-chemical calculations, phenyl vinyl ether exists mainly in the s-trans conformation which is characterized by concurrent p-π* interaction of the oxygen atom with both unsaturated fragments. Introduction of two methyl groups into the ortho positions of the benzene ring forces the latter to go out from the vinyloxy group plane, leading to loss of p-π* conjugation with the aromatic ring, enhancement of p-π* conjugation with the vinyl group, and transition of the molecule to s-cis conformation. The 1H and 13C NMR data indicated that replacement of both o-methyl groups by tert-butyl makes the s-cis conformer sterically overcrowded even when the aromatic ring is oriented orthogonally with respect to the vinyl group; as
a result, conformational equilibrium is displaced again toward s-trans rotamer. 相似文献
3.
Heung N. Lee S. W. Kim M. G. Hur S. D. Yang W. H. Kim K. Y. Jee 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):617-620
3H and 14C Measurements of the dry active waste (DAW), such as the cotton, paper, and vinyl, generated from a nuclear power plant (NPP)
were conducted with wet oxidation using open vessel equipment based on simulation results. The recovery efficiency with the
simulated samples was around 93% with a relative standard deviation (RSD) of 1–3%. A liquid scintillation counter (LSC) was
used for counting and adjusted to a quenching correction curve. The counting value was evaluated for the minimum detectable
activity (MDA), which was found to be about 4 × 10−1 Bq/g for 3H and 2 × 10−2 for 14C when approximately 5 g of the samples were measured. The measured DAW samples for the cotton, paper, and vinyl generated
from NPP achieved of RSD values of 25, 25, and 60%, respectively, for 3H and 0–50% for 14C. 相似文献
4.
Yu. K. Grishin I. P. Gloriozov S. M. Gerdov V. A. Roznyatovsky L. L. Frolova A. V. Kuchin Yu. A. Ustynyuk 《Russian Chemical Bulletin》2008,57(8):1689-1696
The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by 2H-{1H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes
and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally
and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2)
atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group.
For Part 2, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008. 相似文献
5.
Jiri Brus Hana Petříčková Jiri Dybal 《Monatshefte für Chemie / Chemical Monthly》2002,133(12):1587-1612
Summary. A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of
materials is presented. The abilities of the 2D 1H–1H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental
mobility and from undesired coherence transfer are discussed. Basic principles of 1H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative
and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in
heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane
networks. Particular attention is devoted to the determination of the 1H–1H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the 13C–13C correlation mediated by 1H–1H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed.
Corresponding author. E-mail: brus@imc.cas.cz
Received May 28, 2002; accepted (revised) July 1, 2002 相似文献
6.
Summary. The structure of 2-amino-4-aryl-1-arylideneaminoimidazoles in DMSO-d6 solution was investigated by means of NMR spectroscopic methods (1H, 13C, 15N). From these data the (E)-configuration at the excocyclic C=N bond and a strong preference for the conformer with the imidazole H-5 and the N=CH proton being spatially close (s-trans regarding the N–N bond) can be concluded. Reaction of the title compounds with acetic anhydride leads to mono and diacylation at the 2-amino group, whereas treatment with pivalic anhydride exclusively affords the corresponding monoacyl product. The mono- and diacylation products exhibit similar configurational and conformational properties as the parent compounds. 相似文献
7.
S. Pommé E. García-Toraño G. Sibbens S. Richter R. Wellum A. Stolarz A. Alonso 《Journal of Radioanalytical and Nuclear Chemistry》2008,277(1):207-210
High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in 235U. Besides the 235U peaks, separate peaks belonging to impurity traces of 234U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of
the half-lives of 238U and 235U was determined via the activity ratio of 234U and 235U in the materials. As an intermediate link, the 234U/238U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting
half-life ratio T
1/2(238U)/T
1/2(235U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al. 相似文献
8.
S. K. Aggarwal D. Alamelu P. M. Shah N. N. Mirashi 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):771-774
Determination of 241Am/243Am ratios is required for vanous purposes including assay of Am by isotope dilution techniques. Alpha-spectrometry on electrodeposited
sources is a preferred technique for this determination. However, there is an inherent problem of tail contribution which
necessitates the use of suitable algorithms to account for the same. Recently, in the frame of a Coordinated Research Program
(CRP) of the International Atomic Energy Agency (IAEA), WinALPHA software has been developed which is a combination of an
asymmetrical Gaussian for the main part of the peak and a low energy function. Therefore, it was of interest to compare the
use of this algorithm with the routinely used method, in our laboratory, based on geometric progression (G. P.) decrease.
Since, there are no reference materials available commercially for 241Am/243Am ratios, synthetic mixtures covening a wide range (0.3 to 2.0) of 241Am/243Am α-activity ratios were used and un-ignited electrodeposited sources were prepared for α-spectrometry. The α-spectra obtained using PIPS detector, were evaluated using the two algonthms The 241Am/243Am α-activity ratios obtained were also compared with those determined by thermal ionization mass spectrometry (TIMS). An agreement
of about 1% was obtained in the 241Am/243Am ratios determined by the two methods and also by using the two algorithms for α-spectrum evaluation. 相似文献
9.
A. G. Nozad S. Meftah M. H. Ghasemi M. Aghazadeh 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(13):2270-2277
DFT calculations of electric field gradient (EFG) tensors at the sites of 14N, 17O, and 2H nuclei are carried out to characterize the hydrogen bond (HB) interactions in the sulfapyridine crystal structure. One-molecule
(monomer) and hydrogen-bonded hexameric cluster models of sulfapyridine are constructed according to available X-ray coordinates
where the proton positions are optimized. Then, EFG tensors are calculated for both monomer and target molecule in the hexameric
cluster of sulfapyridine to show the effect of HB interactions on the tensors. The calculated EFG tensors are converted to
the experimentally measurable nuclear quadrupole resonance (NQR) parameters: quadrupole coupling constant (C
Q
) and asymmetry parameter (η
Q
). The results reveal different contribution of various nuclei to N-H⋯N and N-H⋯O HB interactions in the cluster where the
N2 and O1 have major contributions. The computations are performed with B3LYP and B3PW91 functionals DFT method and 6-311+G*
and 6-311++G** standard basis sets using the Gaussian 98 package. 相似文献
10.
L. A. Baltina O. Kunert A. A. Fatykhov R. M. Kondratenko L. V. Spirikhin L. A. BaltinaJr. F. Z. Galin G. A. Tolstikov E. Haslinger 《Chemistry of Natural Compounds》2005,41(4):432-435
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. 相似文献
11.
The structure of galactomannans isolated from seeds of G. delavayi and G. aquatica was studied by 1H and 13C NMR spectroscopy. It was found that the galactomannans consisted mainly of β-1-4-bound mannopyranoses, a part of which was substituted on the C-6 hydroxyl by terminal units of α-galactopyranose.__________Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 12–13, January–February, 2005. 相似文献
12.
The 1H NMR spectra (working frequencies of 500 and 600 MHz) of polychloroprenes are studied. The spin systems of protons for monomer
units of different configurations (1,2, 3,4, 1,4-cis-and 1,4- trans- units), as well as for dyad and triad combinations of 1,4 units, are classified. A high working frequency, the method of
double resonance, and the calculation of chemical shifts by empirical increments make it possible to refine the assignment
of 1H NMR signals. 相似文献
13.
A. V. Il’yasov N. K. Gaisin B. I. Buzykin R. B. Zaripov 《Russian Chemical Bulletin》2010,59(8):1506-1511
The 1H spin-lattice relaxation times of the proton-bearing groups and the 31P spin-lattice relaxation times in C-phosphorylated oximes R1C(=NOH)P(=O)R2R3 (R1 = Ph, R2 = R3 = OMe; R1 = Ph, R2 = OMe, R3 = OCH2CH2Br; R1 = PhCH2, R2 = R3 = OCHMe2) and dioxime R2P(=O)C(=NOH)(CH2)4C(=NOH)P(=O)R2 (R = OMe) in DMSO-d6 were measured. The characteristic reorientation times of the whole molecules were estimated using the measured values of
the 1H relaxation times and the results of semiempirical PM3 quantum chemical calculations of the molecular geometries. The reorientation
times were used to identify the contributions of different relaxation mechanisms to the rate of 31P spin-lattice relaxation. The anisotropy of the chemical shielding of 31P nuclei was evaluated from the difference between the 31P relaxation rates measured at 101.27 and 161.92 MHz. 相似文献
14.
Chang Heon Lee Moo Yul Suh Kwang Yong Jee Won Ho Kim 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(1):187-194
A sequential separation procedure has been developed for the determination of 99Tc, 94Nb, 55Fe, 90Sr and 59/63Ni in various radioactive wastes generated from nuclear power plants. Ion exchange and extraction chromatography were adopted
for individual separation of the radionuclides. Precipitation was supplementarily utilized for both purification of the individual
radionuclides and preparation of the radionuclide sources for use in a radioactivity measurement. The chromatographic separation
behavior of the radionuclides both from the sample matrix metals and from one another was investigated using stable metals,
Re (as a surrogate of 99Tc), Nb, Fe, Sr and Ni. The validity of the procedure for reliability and applicability was evaluated by measuring the recovery
of the metal carriers added to synthetic radioactive waste solutions. The recoveries by the chromatographic separation were
in the range of 84.8 to 102.2% with 2s of less than 8.6%, the recoveries by the precipitation being in the range of 84.3 to 97.3% with 2s of less than 10.9%. 相似文献
15.
Two isomeric dibenzofuran carboxaldehydes, namely 2-methoxydibenzo[b,d]furan-1-carbaldehyde (4) and 2-methoxydibenzo[b,d]furan-3-carbaldehyde (5), were synthesized. Formylation of 2-methoxydibenzo[b,d]furan (3) with α,α-dichloromethyl methyl ether and tin(IV) chloride gave a mixture of aldehydes 4 and 5 in 95 % yield and in a 35:65 ratio. Their 1H and 13C NMR spectral signals were not sufficiently resolved in CDCl3 solution to achieve their complete assignment, but this was possible in DMSO-d 6 with the help of 2D-NMR techniques: NOESY for 1H–1H interactions and HSQC and HMQC experiments for 1H–13C correlations. These aldehydes were used in the synthesis of novel β-phenylethylamines and NBOMe derivatives, which are undergoing biological evaluation. 相似文献
16.
Claudia Landstetter Christian Katzlberger 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):467-471
Screening measurements for 3H, 226Ra, 222Rn and 238U in ground water were performed within a ground- and drinking water project in Austria. The aim of this project is to get
an overview of the distribution of natural radionuclide activity concentration levels in ground water bodies. In some cases
this water is used for drinking water abstraction. In this paper methods and results of the screening measurements are presented.
Regions with high activity concentrations were identified and in these regions further investigation for 228Ra, 210Pb and 210Po will be conducted. 相似文献
17.
L. O. Nindakova N. N. Chipanina V. K. Turchaninov M. V. Ustinov B. A. Shainyan 《Russian Chemical Bulletin》2005,54(10):2343-2347
The reaction of di-μ-chlorobis(1,5-cyclooctadiene)dirhodium with (4S, 5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane (1) gave the complex [Rh(cod)(1)]Cl (cod is 1,5-cyclooctadiene). The composition of the complexes CoCl2 · L2 and [Rh(cod)(L2)]X (L2 = 1, (4S,5S)-2,2-dimethyl-4,5-bis(aminomethyl)-1,3-dioxolane, and (4S, 5S)-2,2-dimethyl-4,5-bis(dimethylaminomethyl)-1,3-dioxolane; X = Cl, TfO) was studied using IR and 1H NMR spectroscopy. In the RhI cyclooctadienediamine complexes, the diene molecule forms a stronger bond with the metal atom than that in the cyclooctadienediphosphine
analogs.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2270–2274, October, 2005. 相似文献
18.
Karin Popa Alexandru Cecal Doina Humelnicu Ioan Caraus Camelia L. Draghici 《Central European Journal of Chemistry》2004,2(3):434-445
This study concerns the removal of the 137Cs+ and 60Co2+ β+γ-radioactive ions in Azolla caroliniana Willd. water fern. The living fern and two different types of biosorbent prepared from Azolla caroliniana were tested to remove the above-mentioned radioactive ions from dilute solutions, in the absence and in the presence of the
ionic competition. Effective 137Cs+ and 60Co2+ ions removal from low radioactive wastewaters was demonstrated. The time dependent K
d
(t) values were calculated from the absorption data. These results indicate that removal process achieved equilibrium in about
120 min and that it involves two steps: rapid and slow absorption; the active process (metabolic bioaccumulation on the living
fern) was responsible for above one half of the total removal process. A thin layer radiochromatography study leads to the
conclusion that the biochemical components in which 137Cs+ and 60Co2+ place themselves are of a polysaccharide and lipoid fractions. 相似文献
19.
Gholam Hossein Rounaghi Mohammad Hossein Arbab Zavvar Kataneh Badiee 《Russian Journal of Inorganic Chemistry》2008,53(4):660-664
The equilibrium constants and thermodynamic parameters for complex formation of 18-Crown-6 (18C6) with Tl+, Pb2+, Hg2+, and Zn2+ metal cations have been determined by conductivity measurements in methanol (MeOH)-water (H2O) binary solutions. 18-Crown-6 forms 1:1 complexes with Hg2+ and Zn2+ cations, but in the case of Tl+ and Pb2+ cations, in addition to 1:1 stoichiometry, 1:2 (ML2) complexes are formed in some binary solvents. The thermodynamic parameters (ΔH
c0 and ΔS
c0), which were obtained from the temperature dependences of equilibrium constants, show that in most cases the complexes are
enthalpy destabilized but entropy stabilized. Non-linear behavior is observed between the equilibrium constants (log K
f
) of complexes and the composition of the mixed solvent. The selectivity of the ligand for these metal cations is sensitive
to the solvent composition, and, in some cases, the selectivity order is reversed in certain compositions of the mixed solvent.
The results also show that the mechanism of complexation reactions and the stoichiometry of complexes of some metal cations
change with the nature and even with the composition of the mixed solvent.
The article was submitted by the authors in English. 相似文献
20.
A. A. Kamyshova A. Z. Kreindlin P. V. Petrovskii A. S. Peregudov Yu. A. Borisov A. A. Koridze 《Russian Chemical Bulletin》2005,54(12):2805-2812
The reaction of [Cp*2RuBr]+Br− with bromine in CH2Cl2 (CD2Cl2) in an inert atmosphere at room temperature produces the complexes [Cp*Ru(Br)C5Me4CH2Br]+Br3
− (syn conformer), [Cp*Ru(Br)C5Me3(CH2Br)2]+ (syn and anti conformers), and [Ru(Br)(C5Me4CH2Br)2]+ (syn conformer). All complexes were characterized by 1H and 13C NMR spectroscopy; the former complex, by elemental analysis. These complexes were also prepared by the reaction of [Cp*RuC5Me4CH2]+BF4
− with bromine in CH2Cl2.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2712–2718, December, 2005. 相似文献