Retention of fullerenes by octadecyl silica. Correlation with NMR spectra at low temperatures

1995 ◽  
Vol 40 (9-10) ◽  
pp. 507-512 ◽  
Author(s):  
H. Ohta ◽  
Y. Saito ◽  
K. Jinno ◽  
J. J. Pesek ◽  
M. T. Matyska ◽  
...  
Keyword(s):  
Low Temperatures ◽  
Nmr Spectra ◽  
Octadecyl Silica

Constant Temperature Dewar for NMR Spectra at Low Temperatures

1966 ◽  
Vol 37 (2) ◽  
pp. 238-239 ◽  
Author(s):  
W. B. Rose ◽  
J. W. Nebgen ◽  
F. I. Metz
Keyword(s):  
Constant Temperature ◽  
Low Temperatures ◽  
Nmr Spectra

Rotational Tunnelling of CD3Groups in Molecular Crystals as Studied by NMR Spectra

1988 ◽  
Vol 43 (3) ◽  
pp. 219-227 ◽  
Author(s):  
Z. T. Lalowicz ◽  
Ulrike Werner ◽  
W. Müller-Warmuth
Keyword(s):  
Low Temperatures ◽  
Nmr Spectra ◽  
Spectral Response ◽  
Molecular Crystals ◽  
Numerical Calculations ◽  
Methyl Groups ◽  
H Nmr ◽  
Dipole Interactions ◽  
Large Tunnel

Abstract Tunnelling frequencies of rotating CD3 groups in solids between about 20 kHz and 2 MHz may be obtained from the 2H NMR spectra. The theory of the spectral response is developed where quadrupole and dipole-dipole interactions as well as rotational tunnelling are taken into account. Features characteristic of tunnelling, which distinguish the spectra from those of rapidly reorienting deuterated methyl groups, are found from analytically calculated spectra even for the case of very large tunnel splittings. Numerical calculations have been performed for various conditions to deter­ mine the tunnel frequency. Experimental spectra measured at 45 MHz and low temperatures have revealed the appearance of rotational tunnelling in CD3I, CD3COONa, and (CD3COO)2Cu • H2O. In the latter case, a tunnelling frequency of 608 kHz has been extracted from the spectrum at 27 K.

Konformative Beweglichkeit flexibler Ringsysteme. Untersuchungen mit Hilfe der Protonenresonanz-Spektroskopie

1966 ◽  
Vol 21 (4) ◽  
pp. 320-324 ◽  
Author(s):  
S. Kabuss ◽  
A. Lüttringhaus ◽  
H. Friebolin ◽  
R. Mecke
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Ring Inversion ◽  
Conformational Isomers

The rates of ring-inversion of six- and seven-membered cyclic trisulfides were investigated by nmr-spectroscopy. The JG#-values are higher than those of the corresponding disulfides. but are not high enough for separation of conformational isomers.At low temperatures the nmr-spectra in some cases show the signals of two different conformers.For certain examples simple symmetry-considerations allow the identification of the actual conformation.

Direct observation of dienols produced by photochemical enolisation of α,β-unsaturated ketones: rates and activation parameters for dienol reketonisation via a 1,5-hydrogen shift

1987 ◽  
Vol 65 (8) ◽  
pp. 1867-1872 ◽  
Author(s):  
Randy M. Duhaime ◽  
Alan C. Weedon
Keyword(s):  
Activation Energy ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Arrhenius Plot ◽  
Activation Parameters ◽  
Activation Entropy ◽  
Hydrogen Shift ◽  
Unsaturated Ketones ◽  
Ultraviolet Light Irradiation ◽  
Stable Solutions

The production of stable solutions of Z-dienols by ultraviolet light irradiation of α,β-unsaturated ketones at low temperatures (ca. −76 °C) in d4-methanol is reported. The rates of reketonisation of the dienols via a 1,5-sigmatropic hydrogen shift were determined at various temperatures between −43 °C and + 2 °C by monitoring the proton nmr spectra of the dienols. From the data the activation parameters for the reaction were calculated. For the dienol Z-2-hydroxy-4-methyl-2,4-pentadiene, 2, derived from photoenolisation of 4-methyl-3-penten-2-one, 1, the activation energy from the Arrhenius plot is 62 ± 4 kJ/mol, and the activation entropy and enthalpy from the Eyring plot are −87 ± 15 J/mol K and 60 ± 4 kJ/mol, respectively. For the dienol Z-4-tert-butyl-2-hydroxy-2,4-pentadiene, 4, obtained from photoenolisation of 4,5,5-trimethyl-3-hexen-2-one, 3, the activation energy, entropy, and enthalpy were found to be 47 ± 5 kJ/mol, −135 ± 19 J/mol K, and 45 ± 5 kJ/mol, respectively.

Mechanism of the lithium–iodine exchange in an iodothiophene

2005 ◽  
Vol 83 (9) ◽  
pp. 1577-1587 ◽  
Author(s):  
Hans J Reich ◽  
Wesley L Whipple
Keyword(s):  
Nmr Spectroscopy ◽  
Exchange Reaction ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Variable Temperature ◽  
Activation Parameters ◽  
Kinetic Scheme ◽  
Hypervalent Iodine ◽  
Metal Exchange ◽  
Complex Lithium

Solutions of 2-lithio-5-methylthiophene (4) were characterized using DNMR techniques and shown to be a mixture of monomer and dimer in THF–Et2O (3:2). The hypervalent iodine ate complex 5 (Ar2I–Li+), a presumed intermediate in the Li–I exchange with 2-iodo-5-methylthiophene, was observed by 13C and 7Li NMR spectroscopy at low temperatures (–130 °C). At higher temperatures, the ate complex coalesced with 2-lithio-5-methylthiophene. A kinetic scheme was developed, which accounts for the exchange of the monomer 4M, dimer 4D, and 2-iodo-5-methylthiophene (6) with the ate complex 5. The rates of the various exchanges were obtained through a DNMR analysis of the variable temperature 13C and 7Li NMR spectra, and the thermodynamic and activation parameters were calculated. The monomer 4M and the ate complex 5 have similar reactivity as aryl donors in the Li–I exchange reaction, but 4M is at least 1000 times as reactive as the dimer 4D towards the iodide.Key words: halogen–metal exchange, lithium iodinate, iodine ate complex, lithium reagent, aggregate reactivity.

Restricted rotation about arene–oxygen bonds in some 1,3-di-tert-butyl-2-methoxyarenedicarbonylphosphorus(III)chromium compounds

1984 ◽  
Vol 62 (11) ◽  
pp. 2566-2569 ◽  
Author(s):  
Eva M. Campi ◽  
Bryan M. K. Gatehouse ◽  
W. Roy Jackson ◽  
Ian D. Rae ◽  
Margaret G. Wong
Keyword(s):  
Crystal Structure ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Hindered Rotation ◽  
Methyl Group ◽  
Tert Butyl ◽  
H Nmr ◽  
Free Energy Of Activation ◽  
Chromium Compounds ◽  
Related Compounds

The 1H nmr spectra of 1,3-di-tert-butyl-2-methoxybenzenedicarbonyltriphenylphosphinechromium (5) and some related compounds at low temperatures show the presence of two species which interconvert with free energy of activation near 50 kJ mol−1. The species differ in the orientation of the methoxy with respect to the chromium, since the same type of process is observed in a chelate complex in which a phosphinite ligand on chromium is also attached to the arene. Hindered rotation about the arene–chromium axis is not involved. The crystal structure of 5 shows the Ph3P anti to the methoxy and the O-methyl group proximal to chromium.

Ternary rhombohedral Laves phases RE2Rh3Ga (RE = Y, La–Nd, Sm, Gd–Er)

2017 ◽  
Vol 72 (4) ◽  
pp. 289-303 ◽  
Author(s):  
Stefan Seidel ◽  
Oliver Janka ◽  
Christopher Benndorf ◽  
Bernhard Mausolf ◽  
Frank Haarmann ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Susceptibility ◽  
Rare Earth ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
X Ray Diffraction ◽  
Laves Phases ◽  
X Ray ◽  
Arc Melting ◽  
Pauli Paramagnetism

Abstract:The ordered Laves phases RE2Rh3Ga (RE=Y, La–Nd, Sm, Gd–Er) were synthesized by arc-melting of the elements and subsequent annealing. The samples were characterized by powder X-ray diffraction (XRD). They crystallize with the rhombohedral Mg2Ni3Si type structure, space group R3̅m. Three structures were refined from single crystal X-ray diffractometer data: a=557.1(1), c=1183.1(2), wR2=0.0591, 159 F2 values, 10 variables for Y2Rh3Ga, a=562.5(2), c=1194.4(2) pm, wR2=0.0519, 206 F2 values, 11 variables for Ce2Rh3Ga and a=556.7(2), c=1184.1(3) pm, wR2=0.0396, 176 F2 values, 11 variables for Tb2Rh3Ga. The Rh3Ga tetrahedra are condensed via common corners and the large cavities left by the network are filled by the rare earth atoms. The RE2Rh3Ga Laves phases crystallize with a translationengleiche subgroup of the cubic RERh2 Laves phases with MgCu2 type. Magnetic susceptibility measurements reveal Pauli paramagnetism for Y2Rh3Ga and La2Rh3Ga. Ce2Rh3Ga shows intermediate cerium valence while all other RE2Rh3Ga phases are Curie–Weiss paramagnets which order magnetically at low temperatures. The 89Y and 71Ga solid state nuclear magnetic resonance (NMR) spectra of the diamagnetic representative Y2Rh3Ga show well-defined single resonances in agreement with an ordered bulk phase. In comparison to the binary Laves phase YRh2 a strongly increased 89Y resonance frequency is observed owing to a higher s-electron spin density at the 89Y nuclei as proven by density of states (DOS) calculations.

Dioxobis(Carboxylato)Chromium(VI) and Oxo(Carboxylato)Chromium(III): Reactions of CrO3 with Carboxylic Acid Anhydrides

1984 ◽  
Vol 39 (12) ◽  
pp. 1702-1705 ◽  
Author(s):  
Ramesh Kapoor ◽  
Ramneek Sharma ◽  
Pratibha Kapoor
Keyword(s):  
Carboxylic Acid ◽  
Ir Spectra ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Room Temperature ◽  
Equimolar Ratio ◽  
H Nmr ◽  
Chromium Vi ◽  
Polar Organic Solvents ◽  
Acid Anhydrides

Reactions of carboxylic acid anhydrides [(RCO)2O where R = CH3, C2H5, n-C3H7 and CHCl2] with excess of chromium (VI) oxide at low temperatures yield chromyl carboxylates, CrO2(OOCR)2. These compounds are non-conducting in polar organic solvents. IR spectra suggest the presence of both unidentate and bidentate carboxylato groups and discrete Cr = 0 units. The 1H NMR spectra show the presence of only one type of carboxylato group.Reactions of carboxylic acid anhydrides with CrO3 in equimolar ratio yield reduced chromium(III) com pounds o f the type CrO(OOCR) at room temperature. Their millimolar solutions in C6H5NO2, CH3NO2 and CH3CN are non-conducting. IR spectra, magnetic susceptibility and some other properties have been investigated. Both types of compounds are polymeric in nature having covalent structures.

scholarly journals Nuclear magnetic resonance on $LaFeAsO_{0.4}H_{0.6}$ at 3.7 GPa

2019 ◽  
Vol 11 ◽  
pp. 110002
Author(s):  
Naoki Fujiwara ◽  
Masayuki Takeuchi ◽  
T. Kuwayama ◽  
S. Nakagawa ◽  
Soshi Iimura ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Properties ◽  
Relaxation Time ◽  
Magnetic Resonance ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Spin Excitations ◽  
Iron Based ◽  
Spin Moments ◽  
Ordered State

A prototypical electron-doped iron-based superconductor $LaFeAsO_{1-x}H_x$ undergoes an antiferromagnetic (AF) phase for $x  \geq 0.49$. We performed NMR measurements on $LaFeAsO_{0.4}H_{0.6}$ at 3.7 GPa to investigate the magnetic properties in the vicinity of a pressure-induced QCP. The linewidth of $~^1H$-NMR spectra broadens at low temperatures below 30 K, suggesting that the ordered spin moments remain at 3.7 GPa. The coexistence of gapped and gapless spin excitations was confirmed in the ordered state from the relaxation time $T_1$ of $~^{75}As$. The pressure-induced QCP is estimated to be 4.1 GPa from the pressure dependence of the gapped excitation.

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