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91.
A new technique is proposed to indirectly record with high sensitivity the nuclear magnetic resonance of nuclei with a low gyromagnetic ratio. The method relies on a coherent transfer of transverse magnetization to nuclei of high gyromagnetic ratio. 相似文献
92.
93.
Ernst Peter Müller 《Helvetica chimica acta》1982,65(5):1617-1626
Synthesis of 5,6-Ephnino-5,6-dihydro-β-ionone In order to synthesize the title compound 5 the 2-azidoalcohols 3 and 4 were treated with various nucleophilic phosphorus compounds. It was found that the course of the reaction depends strongly upon the kind of nucleophilic phosphorus derivative used. 相似文献
94.
Roswitha Stejskal Ernst Urban Horst Völlenkle 《Monatshefte für Chemie / Chemical Monthly》1991,122(3):145-156
Summary Oxidation of isobenzofuranone1 yielded in a diastereoselective reaction epoxide2. Acidolysis of2 resulted in a mixture oftrans-glycols6 a (88%) and7 a (4%), which were separated by crystallization. The relative configuration of6 a and7 a at the chiral centers 3 a, 5, 6, and 7 a was determined by1H-NMR-spectroscopy and X-ray analysis of O-acetylated and 7 a-methylated derivatives. 相似文献
95.
The hyperfine structure of the X2∑+, υ = 0 state of 88Sr35Cl has been investigated using microwave—optical polarization spectroscopy. Resolution of the hyperfine structure in transitions between low-lying rotational states has allowed the first determination of magnetic dipole and electric quadrupole coupling constants. The results are: b = 18.663(89) MHz, c = 7.72(30)MHz, and eqQ = 3.96(84) MHz. 相似文献
96.
Harth E Van Horn B Lee VY Germack DS Gonzales CP Miller RD Hawker CJ 《Journal of the American Chemical Society》2002,124(29):8653-8660
A novel approach is presented for the controlled intramolecular collapse of linear polymer chains to give well-defined single-molecule nanoparticles whose structure is directly related to the original linear polymer. By employing a combination of living free radical polymerization and benzocyclobutene (BCB) chemistry, nanoparticles can be routinely prepared in multigram quantities with the size being accurately controlled by either the initial degree of polymerization of the linear chain or the level of incorporation of the BCB coupling groups. The latter also allows the cross-link density of the final nanoparticles to be manipulated. In analogy with dendritic macromolecules, a significant reduction of up to 75% in the hydrodynamic volume is observed on going from the starting random coil linear chains to the corresponding nanoparticles. The facile nature of the living free radical process also permits wide variation in monomer selection and functional group incorporation and allows novel macromolecular architectures to be prepared. Furthermore, the use of block copolymers functionalized with benzocyclobutene groups in only one of the blocks gives, after intramolecular collapse, a hybrid architecture in which a single linear polymer chain is attached to the globular nanoparticle. 相似文献
97.
Williamson PT Verhoeven A Ernst M Meier BH 《Journal of the American Chemical Society》2003,125(9):2718-2722
Rotational-resonance magic-angle spinning NMR experiments are frequently used to measure dipolar couplings and to determine internuclear distances. So far most measurements were performed on samples containing isolated spin pairs. Thus, extensive structure elucidation, for example in biomolecules, requires the preparation of a whole set of doubly labeled samples. Here, we describe the analysis of the rotational-resonance polarization-exchange curves obtained from a single, uniformly labeled sample. It is shown experimentally that, at a magnetic field of 14.09 T, the rotational-resonance conditions in uniformly (13)C-labeled threonine are sufficiently narrow to permit the measurement of five distances between the four carbon spins with an accuracy of better than 10%. The polarization-exchange curves are analyzed using a modified two-spin model consisting of the two active spins. The modified model includes an additional offset in the final polarization, which comes from the coupling to the additional, passive, spins. The validity of this approach is experimentally verified for uniformly (13)C-labeled threonine. The broader applicability of such a model is demonstrated by numerical simulations which quantify the errors as a function of the most relevant parameters in the spin system. 相似文献
98.
Tetrakis(trifluoromethyl) cyclotetraarsane (F3CAs)4 ( 2 ) was used to repeat the UV initiated [4+2]‐cycloaddition reaction of the diarsene F3CAs=AsCF3 ( 1 ) with cyclohexa‐1,3‐diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X‐ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E‐configuration. 2 was also applied for [2+2]‐cycloaddition reactions of 1 with tBuC≡P and MeC≡CNiPr2, but in contrast to positive results with (F3CP)4 the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π‐donor ligand to the Pd(PPh3)2 complex fragment yielding η2‐bis(trifluoromethyl)diarsene‐bis(triphenylphosphane)‐palladium(0) 5 , which was characterized by X‐ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1 , generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]‐cycloadduct with 1‐di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3‐dimethyl‐1,3‐butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F3CP=PCF3. 相似文献
99.
The valence-level photoelectron spectrum of CO absorbed on copper surfaces exhibits extra features in the region 10–20 eV below EF which are attributed to multielectron excitations. We have recorded the satellite intensity as a function of photon energy in the system CO/Cu(110) using synchrotron radiation. It is found that the occurrence of all satellites, including some which are observed for the first time, can be explained in terms of the SCF Xα SW model calculations by Messmer et al. 相似文献
100.
Ernst Bayer Gerd Wahl und Heinz Günther Witsch 《Fresenius' Journal of Analytical Chemistry》1961,181(1):384-390
Zusammenfassung Es werden zwei neue, sehr selektive Trennflüssigkeiten, Äthylenglykol-bis(propionitril)-äther und Glycerin-tri(propionitril)-äther, angegeben. Die Trennflüssigkeiten sind so selektiv wie ,-Bis(propionitril)-äther, erlauben aber höhere Arbeitstemperaturen von 140° bzw. 170°C. An Säulen kleinen Querschnittes wird die präparative Trennung größerer Mengen unter Ausnutzung der Selektivität dieser Trennflüssigkeiten aufgezeigt.Die Trennwirksamkeit und die Belastbarkeit von Säulen verschiedenen Durchmessers zwischen 1–10 cm wird angegeben. Die Trennwirksamkeit liegt in der gleichen Größenordnung wie die der analytischen Säulen. Die Belastbarkeit steigt proportional dem Querschnitt an.I. Mitteilung: E. Bayer u. H. G. Witsch, diese Z. 170, 278 (1959). 相似文献