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.

Diurnal Activity in the Dusky Cockroach, Ectobius lapponicus L. (Blattodea)

1971 ◽  
Vol 2 (2) ◽  
pp. 132-138 ◽  
Author(s):  
Hans Dreisig
Keyword(s):  
Relative Humidity ◽  
Constant Temperature ◽  
Low Temperatures ◽  
Laboratory Experiments ◽  
Dark Period ◽  
Light Period ◽  
Total Darkness ◽  
Diurnal Activity ◽  
Males And Females ◽  
The Difference

AbstractThe activity of the cockroach Ectobius lapponicus was found to differ in males and females in the field, the males being active during the afternoon, the females after sunset. The difference was thought to be due to an inhibition by low temperatures in the males, displacing the activity towards an earlier period of the day. This is in accordance with a theory concerning sensitization, and different thresholds of release dependent on light and temperature as established for the stridulation in Orthoptera Ensifera and the locomotion in a domestic cockroach. A relationship between the amount of activity and the relative humidity was found in the nymphs. Laboratory experiments showed that the activity at constant temperature was released by a change from light to darkness. If low temperatures were applied during the dark period, the activity was displaced to the latter half of the light period. The influence of illumination on the activity was investigated, a faint illumination being more favourable than total darkness.

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.

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

The Fate of 14C Labeled Food Ingested by Underyearling Sockeye Salmon, Oncorhynchus nerka, in Relation to Temperature and Ration

1980 ◽  
Vol 37 (7) ◽  
pp. 1184-1192 ◽  
Author(s):  
R. M. Biette ◽  
G. H. Geen
Keyword(s):  
Constant Temperature ◽  
Low Temperatures ◽  
Sockeye Salmon ◽  
Oncorhynchus Nerka ◽  
Growth Potential ◽  
Short Term ◽  
Respiration Rates ◽  
Cyclic Temperature ◽  
Temperature Constant ◽  
Ration Size

Underyearling sockeye salmon (Oncorhynchus nerka) provided rations likely available in nature grow more rapidly when held under cyclic than under constant temperature. The basis of this enhancement was investigated by following the short-term fate of labeled food in young sockeye fed low (3.4% dry body wt/d) and moderate (6.4% dry body wt/d) rations and maintained under constant and cyclic temperatures. These experiments, corrected for low 14C measured rates of respiration, indicated that growth potential of young sockeye is greater under cyclic temperatures because of the higher respiration rates at constant high temperatures and the greater rates of defecation and excretion at low temperatures. The difficulties in estimating respiration rates from 14CO2 measurements are emphasized.Key words: sockeye salmon, 14C-labeled feeding, incorporation, respiration, excretion, defecation, diel vertical migration, diel cyclic temperature, constant temperature, ration size

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