排序方式: 共有48条查询结果,搜索用时 31 毫秒
1.
The crystal structure of the title compound has been determined from X-ray diffractometer data by direct methods, and refined by full matrix least squares techniques to R = 0·057 for 1231 reflections. The crystals are monoclinic, space group C2/C, cell dimensions a = 1665, b = 987, c = 1443 pm, β = 107·37° and Z = 8. The conformation of the tetrahydro-1,2-oxazine ring is a chair with the N-substituent equatorial. There is evidence of significantly greater torsional angles around the N and O atoms than around the ring C atoms, showing the ring to be more puckered than cyclohexane. The hydrogen bond is between the acid group on one molecule and the ring nitrogen on its neighbour. 相似文献
2.
Frank G. Riddell Eric S. Turner Alan R. Katritzky Ranjan C. Patel Fernando M.S. Brito-Palma 《Tetrahedron》1979,35(11):1391-1398
The synthesis and variable temperature 1H and 13C NMR spectra of three tetrahydro-1,2,4-oxadiazines are reported. The N(4)-Me inversion barriers are 6.8–7.0 (ax→ts) and 7.4–7.9 kcal mol?1 (eq→ts) with ΔG° 0.6–0.9 kcal mol?1. The N(2)-Me inversion barriers are 10.4–11.4 (ax→ts) and 11.6–13.1 kcal mol?1 (eq→ts) with ΔGδ 1.2–1.7 kcal mol?1. The barrier to ring inversion is ca. 12.7 kcal mol?1. “R value” analysis shows the ring to have a 56.5±2δ dihedral angle about the C(5)-(6) bond, indicative of the expected chair conformation. 相似文献
3.
The solid-state CP/MAS 13C-NMR spectra (cross-polarization/magic-angle spinning 13C-NMR) of eight lower cyclic and one linear oligomers and several polymers of (R)-3-hydroxybutanoic acid (3-HB) are reported. The polymeric samples of different origin and molecular weight give remarkably similar and well resolved spectra, indicating considerable similarity in the conformations of the molecules and homegeneity in the solid-state environment. The crystalline cyclic oligomers 1 – 8 containing 3–9 units of 3-HB give very well resolved spectra. The number of nonequivalent positions in the solid state can be identified and is in accord with structures from X-ray diffraction where these were determined. The spectra of the oligolides become increasingly similar to those of the polymer as the ring size increases. This spectral evidence supports the view of a homogeneous and well defined conformation for the polymeric material (as proposed previously, based on other experiments). 相似文献
4.
The chemiluminescence from stabilized nylon 66 fibers during oxidation above Tg has been studied to determine the activation energies of the initiation, propagation and termination reactions. When oxygen is admitted to a nylon 66 sample heated in an inert atmosphere, a pulse of chemiluminescence is observed corresponding to a nonstationary alkyl peroxy radical concentration in the polymer. The analysis of the decay to the steady state can provide kinetic data for peroxy radical reactions in the induction period of the oxidation and the effect of stabilizers on these reactions. 相似文献
5.
6.
R Bonfiglio RC King TV Olah K Merkle 《Rapid communications in mass spectrometry : RCM》1999,13(12):1175-1185
A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
7.
Samit Mandal J Gerl H Geissel K Hauschild M Hellström Z Janas I Kojouharov Y Kopatch RC Lemmon P Mayet Z Podolyak PH Regan H Schaffner C Schlegel J Simpson HJ Wollersheim 《Pramana》2001,57(1):161-164
Feasibility of gamma-ray spectroscopy at relativistic energies with exotic heavy-ions and new generation of germanium detectors
(segmented Clover) is discussed. An experiment with such detector array and radioactive is discussed. 相似文献
8.
We report measurements of non-linear charge transport in epitaxial (La1−x
Pr
x
)0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the
highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage
characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven
charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters
dispersed in a CO background. 相似文献
9.
The 1H NMR spectra of thirteen dihydro-1,2-oxazine derivatives are reported. Spin decoupling allows analysis of the spectra, features of which include homoallylic couplings of +2 to +2·5 Hz, allylic couplings of ?1·5 to ?1·7 Hz and vicinal couplings across sp2 to sp3 carbon–carbon bonds of +2·9 to +3·7 Hz. 相似文献
10.
Füssl A Schleifenbaum A Göritz M Riddell A Schultz C Krämer R 《Journal of the American Chemical Society》2006,128(18):5986-5987
Conjugation of usually impermeable peptide nucleic acids (PNA) to the chelator 2,2':6',2' '-terpyridine strongly promotes cellular and nuclear uptake by cultured HeLa cells. Cellular accumulation is further enhanced in the presence of extracellular Zn2+. 相似文献