Error analysis for optimized inversion recovery spin-lattice relaxation measurements

Sass, M; Ziessow, D.

doi:10.1016/0022-2364(77)90021-x

Cited by 108 publications

(52 citation statements)

References 6 publications

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“…Ten di †erent evolution times from 0.001 to 5.5 s (9.4 T) or 4 s (14.1 T) were employed and values were calculated T 1 using a three-parameter non-linear least-squares Ðt. 39 The nuclear Overhauser enhancements were meag CKHL sured by a standard method.40 Three or more independent measurements were carried out for all relaxation parameters.…”

Section: Methodsmentioning

confidence: 99%

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Ejchart¹,

Zimniak²,

Oszczapowicz³

et al. 1998

Magn. Reson. Chem.

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Section: Methodsmentioning

confidence: 99%

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Ejchart¹,

Zimniak²,

Oszczapowicz³

et al. 1998

Magn. Reson. Chem.

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“…The temperature dependence of the quasielastic line width can be described by an Arrhenius Ansatz [13,14] RT (10) where r denotes the time between jumps, which is correlated with the time constant for infinite tem perature at the high temperature side of the relaxation curve, cf. (8). The barrier height £a of the rotational potential is then obtained from…”

Section: Resultsmentioning

confidence: 99%

“…All relaxation measurements were carried out applying 180°-t-90c pulse sequences. Tx was determined using an exponen tial fitting procedure [8]. The accuracy of the mea sured Fj-values is estimated to be ±5%.…”

Section: Methodsmentioning

confidence: 99%

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

Burbach

Weiß

1991

Zeitschrift Für Naturforschung A

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Nuclear magnetic resonance (NMR) and inelastic neutron scattering techniques (INS) have been applied to study the rotational motions and methyl group tunneling in tetramethylstibonium iodide, [Sb(CH3)4]I, over a wide temperature range. Parameters describing the [Sb(CH3)4]® cation tum bling and the methyl group reorientation at high temperatures and quantum mechanical tunneling of the methyl groups at low temperatures were determined.The results for INS and NMR experiments at low temperatures can be explained in terms of two crystallographically inequivalent methyl groups CH3(1) and CH3(2), which were established earlier by the crystal structure determination. In the INS spectra two tunneling lines at 22.0 peV for CH3(1) and 1.05 peV for CH3(2) with inelastic intensities in the ratio 3:1 were observed at 7 = 4 K.The activation energies derived from proton NMR spin-lattice relaxation time measurements for the thermally activated methyl group rotation are 1.50 kJ/mol for CH3(1) and 3.81 kJ/mol for CH3(2). They are in accordance with the activation energies obtained from neutron fixed-window measurements.The activation energy for [Sb(CH3)4]® cation tumbling is 50.9 kJ/mol as determined from the high temperature spin-lattice relaxation behaviour.Rotational potentials for the methyl groups are derived. For both kinds of inequivalent methyl groups the threefold potential terms dominate; three-and sixfold potential contributions are shifted by 180°. IntroductionRotational excitations of a methyl group provide a simple example of motional processes in the solid state. They have been studied both at higher tempera tures as thermally activated random reorientation and in the quantum mechanical regime at low temperatures. At very low temperatures the methyl group rotation can be described via quantum mechanical tunneling between the splitted torsional state [1], Increasing the temperature, rotation of the methyl group becomes thermally activated and can be treated classically. In the high temperature limit, additionally tumbling of the whole molecular framework can be activated in case of highly symmetric quasi spherical molecules or ions. Using nuclear magnetic resonance (NMR) meth ods, the activation energies of the thermally activated processes of the methyl group and the molecule as a whole as well as the reorientation rates can be deter mined [2].High resolution inelastic neutron spectroscopy (INS) has provided as suitable tool to determine the tunneling splitting in the quantum mechanical regime. The deter mination of this splitting is a good probe of the height and shape of the hindering potential barriers [3].Investigations of tetramethyl metal compounds with an element of the main group IV of the periodic system as central atom (e.g. tetramethyl lead, tetra methyl tin) have demonstrated that the interpretation of the NMR and INS data can not be described quan titatively without taking into account crystal structure data [4,5].The present investigation was undertaken to study the rotational behaviour of charged X(CH...

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“…Approximate separation of these relaxation contributions can be realized by applying the stochastic diffusion model of multiple internal rotations, developed initially by Wallach (19), and subsequently modified by Levine et al (20,21). In the present case, two motions about the C(5)-C (6) and C(7)-CH3 bonds are considered to be free and independent of the overall molecular reorientation. Restricted rotation about the C(6)-C(7) bond ensures that the two internal motions are independent of one another.…”

Section: Resultsmentioning

confidence: 99%

“…The temperature was controlled to within ?O.l°C by means of a precalibrated copperconstantan thermocouple in the probe insert. The relaxation times were measured by the FIRFT technique (5) and analysed by a three-parameter non-linear procedure (6). The pulse duration for a 180" flip angle, checked at various temperatures, was 29.6 ks.…”

Section: Dmso-d6 Solution Over the Temperature Range 20-100°c Andmentioning

confidence: 99%

Motional behavior of "asperlin" in solution. A ¹³C spin-lattice relaxation study

Dais¹,

Fainos²

1986

Can. J. Chem.

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PHOTIS DAIS and GEORGE FAINOS. Can. J. Chem. 64, 560 (1 986).I3c nuclear magnetic resonance spin-lattice relaxation times (TI) have been used to probe the motional behavior of 5-acetoxy-5,6-dihydro-6-(1,2-epoxypropyl)-2-pyrone ("asperlin") in dimethyl sulfoxide solution. This molecule offers structural features suited to a study of internal motions, i.e., epoxypropyl and methyl internal motions superimposed on an anisotropic overall reorientation. The rigidity of the pyrone ring and its semiplanar conformation result in an overall ellipsoidal shape, and hence the rotational dynamics of asperlin are adequately approximated by the diffusion of a prolate ellipsoid with the major axis passing through the C(2)-H(2) bond. The description of the internal motion of the epoxypropyl ring is strongly model dependent. Furthermore, the relaxation data for the oxirane ring carbons do not uniquely define a dynamic model. Due to similarities in the activation energies of the overall and internal motions, based on temperature-dependent measurements, it has not been feasible to interpret the relaxation data by a single type of motion. Internal rotation of the epoxymethyl substituent is rationalized by applying the stochastic diffusion model of multiple internal rotations. PHOTIS DAIS et GEORGE FAINOS. Can. J. Chem. 64, 560 (1986).On a utilisk les temps de relaxation spin-rCseau (TI) de la rmn du I3c pour Ctudier le comportement des mouvements de 1'acCtoxy-5 dihydro-5,6 (Cpoxy-1,2 propy1)-6 pyrone-2 ("asperlin") en solution dans le dimCthylsulfoxyde. Cette molCcule prCsente des caractCristiques de structure qui sont adaptCes a une Ctude des mouvements internes; il s'agit des mouvements internes de 1'Cpoxypropyle et du mCthyle qui se superposent a une orientation globale anisotrope. La rigidit6 du cycle pyrone et sa conformation semi-planaire lui font adopter une forme globale ellipsoi'dale et l'on peut dCcrire adkquatement la dynamique de la rotation de I'asperlin en faisant I'approximation qu'elle ressemble a la diffusion d'une ellipsoide allongCe avec un axe majeur qui passerait par la liaison C(2)-H(2). La description du mouvernent interne du cycle Cpoxypropyle dCpend beaucoup dy modkle. De plus, les donnies de relaxation des carbones du cycle oxirane ne permettent pas de dCfinir un modkle dyamique. A cause de similaritCs dans les Cnergies d'activation des mouvements globaux et internes, que I'on a obtenues a partir de mesures qui dCpendaient de la tempirature, on n'a pas pu interpreter les donnCes de relaxation par un seul type de mouvement. On a rationalist5 la rotation interne du substituant CpoxymCthyle en appliquant le modkle de diffusion stochastique des rotations internes multiples.[Traduit par le journal]

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Error analysis for optimized inversion recovery spin-lattice relaxation measurements

Cited by 108 publications

References 6 publications

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

Motional behavior of "asperlin" in solution. A ¹³C spin-lattice relaxation study

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Error analysis for optimized inversion recovery spin-lattice relaxation measurements

Cited by 108 publications

References 6 publications

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Comparative13C relaxation study ofR andS isomers of the 1-acetoxyethyl ester of cefuroxime. Influence of C—H bond lengths on relaxation data consistency

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

Motional behavior of "asperlin" in solution. A 13C spin-lattice relaxation study

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Motional behavior of "asperlin" in solution. A ¹³C spin-lattice relaxation study