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1.
Florence Babonneau Christine Toutou Stéphanie Gavériaux 《Journal of Sol-Gel Science and Technology》1997,8(1-3):553-556
17O NMR experiments using enriched water were performed to followthe hydrolysis-condensation process of dimethyldiethoxysilanetetraethoxysilane and a 1/1 mixture of dimethyldiethoxysilane andtetraethoxysilane (H2O/OEt = 0.5; pH = 2). The spectrarecorded over several hours time period were simulated to followquantitatively the variations of residual water, hydroxyl groups(Si–17
H) and oxo bridges (Si–17
–Si). Presence of a resonance signal due oxo bridges between di- andtetrafunctional Si units clearly demonstrates that co-condensationreactions occur to a large extent between the two alkoxides, and that thesebonds are stable during the aging period. 相似文献
2.
The solvent effect on 17O isotropic shielding was computed by different methods: the polarizable continuum model and a mixed approach, including a few real solvent molecules treated as the solute. The experimental data show that the behavior of protic and aprotic solvents is markedly different: we found that the continuum approach describes well the observed shielding at various dielectric constants for aprotic solvents, while the mixed procedure is needed when hydrogen bonds to the magnetic centre are present.Contribution to the Jacopo Tomasi Honorary Issue 相似文献
3.
Hydrolysis of NH4TiOxF5-2x (x0.4) (I) was investigated by 19F, 17O, and 49Ti NMR. The interaction of complex I with water is accompanied by the formation of [TiF6]2- and multinuclear titanium forms. The composition of the main forms resulting from hydrolysis of I has been established. The bonding of titanium octahedra into dimers and other oligomers occurs by formation of hydroxyl bridges, considerably lowering the pH of the solution. Close analogy has been found between hydrolysis of the title complex and that of titanium tetrafluoride. 相似文献
4.
I. Jaymes A. Douy P. Florian D. Massiot J. P. Coutures 《Journal of Sol-Gel Science and Technology》1994,2(1-3):367-370
Mullite has been prepared from a new combination of precursors. An aluminum alkoxide, aluminium isopropoxide, and silicon tetrachloride, are hydrolysed in tetrahydrofuran solution by 17O enriched water. The resulting powder is chemically homogeneous, crystallizing into mullite at 980°C. The structural evolution has been studied by DTA, TGA, XRD and 17O, 27Al and 29Si MAS NMR spectroscopy. 相似文献
5.
6.
Arrigo Forni Irene Moretti Adele Mucci Fabio Prati Luisa Schenetti 《Chemistry of Heterocyclic Compounds》1995,31(9):1071-1078
A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by1H ,13C,17O, and15N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995. 相似文献
7.
The hypothesis and the conclusions of previous 17O NMR studies on the detection of both oxygens of the carboxylic group of Boc-[17O]Tyr(2,6-diClBzl)-OH in DMSO-d6 solution (Tetrahedron Lett.2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the 17O NMR time scale. 相似文献
8.
Hanspeter Kählig Peter Paul Nimmerrichter Wolfgang Robien 《Monatshefte für Chemie / Chemical Monthly》1993,124(1):71-75
Summary Treatment of abietic acid methylester with Hg(OAc)2/MeOH produces a dimethoxy derivative. The determination of the configuration at C-7 of this product by means of 1D- and 2D-NMR-spectroscopic methods is described. The results are verified by application of17O-NMR spectroscopy and comparison with well-established stereochemical dependencies of17O chemical shifts.
17O-NMR-Spectroskopie zur stereochemischen Analyse. Anwendung auf ein Diterpen-Derivat
Zusammenfassung Umsetzung von Abietinsäuremethylester mit Hg(OAc)2/MeOH führt zu einem Dimethoxyderivat. Die Bestimmung der Konfiguration am Zentrum C-7 erfolgt durch Anwendung von 1D- und 2D-NMR-Methoden. Die Resultate konnten durch17O-NMR-Spektroskopie aufgrund der bekannten stereochemischen Verschiebungsabhängigkeit bestätigt werden.相似文献
9.
The relative thermodynamic stabilities of 4,7-dihydro-1,3-dioxepin (4,6-dioxacycloheptene, 1a) and 4,5-dihydro-1,3-dioxepin (3,5-dioxacycloheptene, 1b), and of a number of their 2-substituted derivatives, have been determined by base-catalyzed chemical equilibration in DMSO solution. Without exception, the 4,5-dihydro isomer is the dominating species at thermodynamic equilibrium. The relative stability of the b form is promoted by the presence of a single alkyl group on C-2, whereas two alkyl groups on C-2 have an opposite effect. In general, the thermodynamic parameters H
m
and
Sm
, of isomerization vary unexpectedly with the pattern of substitution at C-2. These trends appear to be derived from significant substituent-induced conformational changes in the b isomer, as suggested by 13C and 17O NMR chemical shift data. 相似文献
10.
I. A. Grigor'ev M. A. Voinov M. A. Fedotov 《Chemistry of Heterocyclic Compounds》2005,41(9):1134-1138
Derivatives of 3-imidazoline 3-oxide have been studied by 14N and 17O NMR methods. Regularities of the influence of substituents and of a hydrogen bond on chemical shifts have been made apparent.
The range of changes of the chemical shifts of the nitrogen and oxygen nuclei of the nitrone group has been determined. Both
in the 17O and in the 14N NMR spectra the signals of the amino derivatives are the highest field signals for the nitrone group, and the lowest field
signals are the signals of the cyano derivatives in the series of derivatives investigated. Depending on the substituent (from
amino to cyano group) the 17O chemical shifts varied over a range ∼155 ppm, but the interval of change of the 14N chemical shifts for the same substituents was ∼110 ppm.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1336–1341. September, 2005. 相似文献
11.
Jorge Antonio Guerrero-Alvarez 《Tetrahedron letters》2007,48(5):795-798
The relationship between the 13C and 17O NMR chemical shifts and the dihedral energies (non-bonding interactions) of 1,4-dioxaspiro[4.4]nonane, 1,4-dioxa- and 6,10-dioxaspiro[4.5]decane, 1,4-dioxa- and 6,11-dioxaspiro[4.6]undecane, 1,5-dioxaspiro[5.5]undecane, 1,5-dioxa and 7,12-dioxaspiro[5.6]dodecane and 1,6-dioxaspiro[6.6]tridecane were analyzed. These data showed correlation of the non-bonding interactions with the chemical shift of the spiranic carbon, as well as a linear relationship between 13C and 17O. 相似文献
12.
Masaaki Abe Kiyoshi Isobe Katsuhiko Kida Akira Nagasawa Atsushi Yagasaki 《Journal of Cluster Science》1994,5(4):565-571
Variable-temperature17O NMR together with51V and103Rh NMR studies on newly prepared vanadium oxide-supported organorhodium(I) fragment(s), [(RhCOD)
n
(V4O12)](4–n)– (n = 1, 2; COD =
4-1,5-cyclooctadiene) indicate that intramolecular rearrangements of RhCOD fragment(s) on a vanadium oxide surface occur in solution. 相似文献
13.
A group of para-substituted bis(acetoxy)iodoarenes has been studied by 17O and 13C NMR. Only one signal for all the oxygens of the acetoxy groups has been observed. Both 17O and 13C chemical shifts of this group show a strong invariance with para substitution. The absence of covalent I-O bonds and an ion pair structure is proposed for the title compounds. 相似文献
14.
Keitaro Kiyosawa 《Journal of solution chemistry》1991,20(6):583-588
Freezing-point depression of mixtures of H
2
16
O and H
2
18
O were measured. The results showed that the freezing point of the mixture rose linearly with an increase in the molal concentration of H
2
18
O. The results suggested the formation of a solid solution of H
2
16
O and H
2
18
O by freezing, similar to that formed by H
2
O–D
2
O, and that H
2
18
O behaves as a different molecule than H
2
16
O. 相似文献
15.
Zhijin Lin 《Journal of Coordination Chemistry》2016,69(9):1411-1418
The number of oxygen-based ligands coordinated to lanthanide ions influences the physical and chemical properties of lanthanide complexes, making this number important to study. We used peak shifts in 17O-NMR spectroscopy to determine the number of individual nonhydroxyl-oxygen-based ligands coordinated to Dy3+. Oxygen-containing organic solvents were used as models to represent oxygen-based ligands to explore the scope of the technique because they contain a range of functional groups that have different electron-donating abilities and steric bulk. The measured coordination numbers of dimethylformamide, dimethyl sulfoxide, acetone, diethyl ether, tetrahydrofuran, di-isopropyl ketone, and hexamethyl acetone were consistent with reasonable values, indicating that 17O-NMR spectroscopy is a useful technique to study the coordination chemistry of nonhydroxyl ligands to lanthanide ions in solution. 相似文献
16.
Emna G. Nasr Ekaterina N. Epova Mathieu Sebilo Dominic Larivire Mohamed Hammami Radhia Souissi Houyem Abderrazak Olivier F. X. Donard 《Molecules (Basel, Switzerland)》2022,27(6)
The olive oil industry is subject to significant fraudulent practices that can lead to serious economic implications and even affect consumer health. Therefore, many analytical strategies have been developed for olive oil’s geographic authentication, including multi-elemental and isotopic analyses. In the first part of this review, the range of multi-elemental concentrations recorded in olive oil from the main olive oil-producing countries is discussed. The compiled data from the literature indicates that the concentrations of elements are in comparable ranges overall. They can be classified into three categories, with (1) Rb and Pb well below 1 µg kg−1; (2) elements such as As, B, Mn, Ni, and Sr ranging on average between 10 and 100 µg kg−1; and (3) elements including Cr, Fe, and Ca ranging between 100 to 10,000 µg kg−1. Various sample preparations, detection techniques, and statistical data treatments were reviewed and discussed. Results obtained through the selected analytical approaches have demonstrated a strong correlation between the multi-elemental composition of the oil and that of the soil in which the plant grew. The review next focused on the limits of olive oil authentication using the multi-elemental composition method. Finally, different methods based on isotopic signatures were compiled and critically assessed. Stable isotopes of light elements have provided acceptable segregation of oils from different origins for years already. More recently, the determination of stable isotopes of strontium has proven to be a reliable tool in determining the geographical origin of food products. The ratio 87Sr/86Sr is stable over time and directly related to soil geology; it merits further study and is likely to become part of the standard tool kit for olive oil origin determination, along with a combination of different isotopic approaches and multi-elemental composition. 相似文献
17.
Liu Yuyan Liu Hongping Guo Yuanqing Liu Xiaoyong Lin Jieli Huang Guangming Gao Hui Li Jinrui 《中国科学B辑(英文版)》2000,43(2):121-128
LMR spectra for v=1←0 transitions of14N16O in X2II1/2, 3/2 states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function
to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral
data of14N16O as well as14N17O and14N18O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision
(1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the
molecular constants of14N17O and14N18O were deduced. 相似文献
18.
本文用水热共沉淀法制备Ce3+掺杂La2O3的前驱体,随后在H2/N2气氛下用高温煅烧法合成了不同Ce3+浓度的掺杂La2O3。由于Ce3+的掺杂,17O固体核磁共振谱图中在698、650和558处出现了新的共振峰;随着Ce3+掺杂浓度的增加,这些峰的强度也随之增强。根据谱峰位置和强度,对谱图进行了归属:698、650处的共振峰应源自与Ce3+相连的四配位O(OCeLa3),558处的信号则来自于与Ce3+相连的六配位O(OCeLa5)。通过17O固体核磁共振能够直接观测与Ce3+直接相连的O显示该方法将可能用于研究稀土掺杂氧化物功能材料。 相似文献
19.
本文用水热共沉淀法制备Ce3+掺杂La2O3的前驱体,随后在H2/N2气氛下用高温煅烧法合成了不同Ce3+浓度的掺杂La2O3。由于Ce3+的掺杂,17O固体核磁共振谱图中在698、650和558处出现了新的共振峰;随着Ce3+掺杂浓度的增加,这些峰的强度也随之增强。根据谱峰位置和强度,对谱图进行了归属:698、650处的共振峰应源自与Ce3+相连的四配位O(OCeLa3),558处的信号则来自于与Ce3+相连的六配位O(OCeLa5)。通过17O固体核磁共振能够直接观测与Ce3+直接相连的O显示该方法将可能用于研究稀土掺杂氧化物功能材料。 相似文献
20.
Erkki Kolehmainen 《Russian Chemical Bulletin》1994,43(4):563-565
Results of multinuclear NMR studies of some heteroorganic compounds have been presented.According to a report at the conference «Current problems of organometallic chemistry» (May 8–13,1994, Moscow).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 614–616, April, 1994. 相似文献