A study of internal rotation in 2-furaldehyde through 13C relaxation times in the rotating frame

1987 ◽  
Vol 52 (2) ◽  
pp. 541-546 ◽  
Author(s):  
Vladimír Mlynárik
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Activation Enthalpy ◽  
Relaxation Times ◽  
Rotating Frame ◽  
Line Shape Analysis ◽  
13C Relaxation Times ◽  
Free Activation Energy ◽  
13C Relaxation ◽  
Good Agreement

Carbon-13 relaxation times in the rotating frame were used to study the exchange between unequally populated rotamers of 2-furaldehyde. Calculated free activation energy and activation enthalpy are in good agreement with the results of 1H line shape analysis. Accuracy and reliability of this method in comparison with the line shape analysis is discussed.

Measurements and analysis of rototranslational absorption spectra of low density H2–Ar mixtures

1988 ◽  
Vol 66 (9) ◽  
pp. 803-809 ◽  
Author(s):  
P. Dore ◽  
A. Filabozzi ◽  
G. Birnbaum
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Low Frequency ◽  
Frequency Component ◽  
Low Density ◽  
Spectral Moment ◽  
Line Shape Analysis ◽  
Induced Dipole ◽  
Good Agreement ◽  
Induced Dipoles

We present new measurements of the rototranslational absorption of H2–Ar mixtures at 195 and 298 K. Measurements were made at densities as low as possible. The first accurate (5% error) rototranslational spectrum of the H2–Ar pair was thus derived. We performed a line-shape analysis of these spectra; as a result, we found a low-frequency component associated with an isotropic overlap induced dipole. We also found an important anisotropic overlap contribution associated with the dominant quadrupolar induction. Through a spectral-moment analysis we determined the intensity of isotropic (λ0 = 2.35 ± 0.15 × 10−3ea0) and anisotropic (λ1 = 0.9 ± 0.1 × 10−3ea0) overlap induced dipoles. The range of the isotropic overlap induced dipole was found to be ρ0 = (0.105 ± 0.010)σ, in very good agreement with the value 0.11 σ frequently assumed in the literature for the range of overlap induced dipoles. Our measurements and the results of our analysis were in good agreement with results of recent computations.

scholarly journals 1H NMR and Calorimetric Measurements on Rabbit Eye Lenses

1995 ◽  
Vol 50 (5-6) ◽  
pp. 410-418 ◽  
Author(s):  
Aleksander Gutsze ◽  
Jerzy Bodurka ◽  
Robert Olechnowicz ◽  
Gerd Buntkowsky ◽  
Hans-Heinrich Limbach
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Time Scale ◽  
Water Exchange ◽  
Relaxation Times ◽  
Proton Nuclear Magnetic Resonance ◽  
Water Molecules ◽  
Line Shape Analysis ◽  
Calorimetric Measurements ◽  
Rabbit Lens

The dynamic properties of water molecules in the rabbit lens were studied by proton nuclear magnetic resonance line shape analysis, measurements of relaxation times as a function of temperature and calorimetric measurements. The experiments prove, as already suggested by other authors, that there are two types of water in the lens of rabbit eyes, namely bound unfreezable hydration water and bulk freezable water. Line shape analysis and relaxometry showed, that this two types of water exist in two different environments, which may be identified as the nucleus and the cortex of the lens. The line shape analysis showed furthermore that water molecules in the rabbit lens has a common spin lattice relaxation time (T1), but two different transverse relaxation times (T2A and T2B). The tentative model of fast water exchange on the T1 time scale and slow water exchange on the T2 time scale, was used to explain experimental proton relaxation data of the rabbit lens. An estimation for this exchange rate Kex by comparing it to the relaxation times is given (T-11 ≪ kex ≪ T-11). It has also been shown by a calorimetric measurements, that the lenses can be easily undercooled to temperatures well below the freezing point of water. The achievable maximum undercooling temperature of the lens is a function of the cooling rate KC , therefore it has to be considered as an experimentally adjustable parameter which is not characteristic for the investigated sample. Thus it must be noted that any previous discussions about the specific value of the temperature of water crystallisation in biological systems need to be carefully reconsidered.

Commentary on the NMR apparent phase transition effect in natrolite, fluor-montmorillionite and other systems: Generalizations when the Arrhenius law applies

1976 ◽  
Vol 54 (3) ◽  
pp. 295-300 ◽  
Author(s):  
H. A. Resing ◽  
D. W. Davidson
Keyword(s):  
Phase Transition ◽  
Water Molecule ◽  
Shape Analysis ◽  
Line Shape ◽  
Activation Enthalpy ◽  
Arrhenius Law ◽  
Transition Effect ◽  
Line Shape Analysis ◽  
Mobile Fraction ◽  
The Mean

In situations where the NMR apparent phase transition effect occurs and the Arrhenius rate law is applicable, it has been shown that the mean activation enthalpy is roughly 37 times the temperature at which the mobile fraction is one-half. This and further generalizations have been applied to proton NMR line-shape analysis of water in natrolite and other systems; the mean activation enthalpy for water molecule diffusion in natrolite is estimated to be 18 kcal/mol.

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond; Adamantan-1-yl 3-Bromo-2,4,6-trimethylphenyl Ketone

1998 ◽  
Vol 63 (7) ◽  
pp. 955-966
Author(s):  
Eva Přibylová ◽  
Miroslav Holík
Keyword(s):  
Thermodynamic Parameters ◽  
Shape Analysis ◽  
Rate Constants ◽  
Line Shape ◽  
Microsoft Excel ◽  
Hindered Rotation ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Coalescence Temperature

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.

Cope rearrangement of 9-methylenebarbaralane. Complete line shape analysis

1973 ◽  
Vol 38 (6) ◽  
pp. 1210-1215 ◽  
Author(s):  
Linda G. Greifenstein ◽  
Joseph B. Lambert ◽  
Michael J. Broadhurst ◽  
Leo A. Paquette
Keyword(s):  
Shape Analysis ◽  
Line Shape ◽  
Cope Rearrangement ◽  
Line Shape Analysis
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