Study of cross - relaxation and molecular dynamics in the solid 3-(trifluoromethyl) benzoic acid by solid state NMR off - resonance (original) (raw)
Related papers
(CH3)4NPF6 is studied by NMR measurements to understand the internal motions and cross relaxation mechanism between the heterogeneous nuclei. The spin lattice relaxation times (T1) are measured for 1H and 19F nuclei, at three (11.4, 16.1 and 21.34 MHz) Larmor frequencies in the temperature range 350–50 K and 1H NMR second moment measurements at 7 MHz in the temperature range 300–100 K employing home made pulsed and wide-line NMR spectrometers. 1H NMR results are attributed to the simultaneous reorientations of both methyl and tetramethylammonium groups and motional parameters are evaluated. 19F NMR results are attributed to cross relaxation between proton and fluorine and motional parameters for the PF6 group reorientation are evaluated.
Applied Magnetic Resonance, 2016
In the present work, a new method for measuring motional parameters using the off-resonance technique was described. The Lipari-Szabo model-free formalism was used to analyze molecular dynamics in a heteronuclear system [1, 2]. Cross-relaxation solid state nuclear magnetic resonance off-resonance experiments were performed on a homebuilt pulse spectrometer operating at the frequency of 30.2 MHz for protons at temperature 173 K. The proton spins were spin-locked in the effective field B e while 19 F spins were continuously saturated for a long time. It was possible to carry out these experiments because a uniquely designed probe was able to produce three slightly differing frequencies on and off-resonance for protons and the frequency of 28.411 MHz for fluorine [3-6]. The off-resonance frequencies can be changed within the range of 30.2-30.6 MHz.
NMR study of 3,4-dimethoxy benzoic acid
Journal of Molecular Structure, 1981
The computed value of the rigid lattice second moment of 3,4-dimethoxy benzoic acid (15.31 gauss' ) agrees fairly well with the experimental value of the second moment (17.01 f 1 gauss2) indicating that the lattice is rigid at 77 K and confirming the proposed model. From the .temperature dependence of the second moment, a transition is observed at room temperature which is attributed to the rotation of methoxy groups.
Solid state proton spin–lattice relaxation in four structurally related organic molecules
Chemical Physics, 2003
We report and interpret the temperature dependence of the proton spin-lattice relaxation rate at 8.50 and 22.5 MHz in four polycrystalline solids composed of structurally related molecules: 2-ethylanthracene, 2-t-butylanthracene, 2ethylanthraquinone, and 2-t-butylanthraquinone. We have been unable to grow single crystals and therefore do not know the crystal structures. Hence, we use the NMR relaxometry data to make predictions about the solid state structures. As expected, we are able to conclude that the ethyl groups do not reorient in the solid state but that the t-butyl groups do. The anthraquinones have a ''simpler'' structure than the anthracenes. The best dynamical models suggest that there is a unique crystallographic site for the t-butyl groups in 2-t-butylanthraquinone and two sites, each with half the molecules, for the ethyl groups in 2-ethylanthraquinone. There are also two sites in 2-ethylanthracene, but with unequal weights, suggesting four sites in the unit cell with lower symmetry than the two anthraquinones. Finally, the observed relaxation rate data in 2-t-butylanthracene is very complex and its interpretation demonstrates the uniqueness problem that arises in interpreting relaxometry data without the knowledge of the crystal structure.
Russian Physics Journal, 2018
Nuclear magnetic resonance (NMR) is one of the most important analytical means of analysis of substances. Recently, NMR with compact magnets and fairly homogeneous fields has been widely used for testing of materials. Nuclear magnetic resonance relaxometry can be used for nondestructive testing of materials by means of NMR-MOUSE sensors [1]. Unlike the longitudinal relaxation time T 1 , the transverse relaxation time T 2 is a more important parameter of nuclear magnetic resonance for characterization of molecular dynamics of amorphous and semicrystalline polymers [2]. Among the most widespread methods of measuring T 2 are the methods of the Hahn echo (HE) and Carr-Purcell-Meiboom-Gill (CPMG) sequence. The Hahn echo and the CPMG sequence do not allow measuring short times Т 2 close to the dead time of the spectrometer and characteristic for vitrified or crystaqllized polymers. The problem of registering short Т 2 times can be solved using the solid-echo (SE). In [3] the destruction of some polymers upon exposure to different factors was investigated by NMR relaxometry methods, and the sensitivity of spin-spin relaxation times Т 2 to artificial polymer aging was demonstrated. The present work studies the specific features of spin-spin relaxation time distributions in a solid polymer depending on the method of registering the transverse magnetization decay and the method of finding the relaxation components. As an examined polymer sample, the outer insulation layer of radio-frequency RK-75 cable made of polyvinyl chloride (PVC) was chosen. 1 H NMR relaxation experiments at a frequency of 13.84 MHz were performed in a weak magnetic field using a Tecmag Apollo spectrometer with TNMR software. A permanent magnet with working sample region 5 mm in diameter and 20 mm long was used. The magnet consisted of two permanent magnets with sizes 60 80 100 mm connected with a U-shaped magnetic core and having a 25 mm gap. The magnetic field induction in the gap was 300 mT. The magnetic field inhomogeneity in the region where the coil with the sample was located was 0.1 mT/cm. The HE, CPMG, and SE sequences and the Ostroff-Waugh (OW) sequence [4] were used to measure the spin-spin relaxation time Т 2. The distributions of the relaxation time Т 2 were obtained by inversion of the integral transformation on the basis of the algorithm described in [5]. Decompositions in exponential and Gauss functions were performed because measurements were carried out at a temperature of 293 K lying below the vitrification temperature of polyvinylchloride. The Т 2 relaxometry is one of the methods of quantitative estimation of the phase composition of multiphase polymers. It is a complicated problem because of the complexity of multiphase composition and the complexity of molecular motion. The Т 2 relaxation signal from the rigid polymer phase is conventionally described by the Abraham or
Concentration and solvent dependence of 33S nuclear magnetic relaxation in benzenesulfonic acid
Journal of Magnetic Resonance (1969), 1989
The first 33S NMR relaxation study of an organic ion in aqueous and nonaqueous electrolyte solution is reported. The 33S NMR spectra were determined as a function of benzenesulfonic acid concentration in water, formamide, N-methylformamide, and a binary mixture of formamide plus I8 mol% water. Linear regression analysis was used to estimate relaxation times at infinite dilution. The 33S relaxation data are discussed in terms of ion-ion and ion-solvent interactions. The data indicate that solvation of benzenesulfonate in water and formamide is very similar, while solvation in N-methylformamide is different.
Anomalous proton spin‐lattice relaxation in organic compounds containing methyl groups
Concepts in Magnetic Resonance Part A, 2019
Temperature measurements of proton spin‐lattice relaxation time performed for acetates ((CH3COO)2Ba, (CH3COO)2Cd, and (CH3COO)2Ca) and acetyl halides ((CH3CO)2O, CH3COBr and CH3COCl) are fitted to a Haupt equation. It is impossible to fit the temperature dependence of T1 protons using the BPP equation. Of importance is the assumption that complex C3 molecular motion of methyl protons takes place. An understanding of the correlation functions of complex C3 reorientation allow for the calculation of the relaxation time, T1, and the second moment of the NMR resonance. The spectral densities are calculated applying Woessner theory of complex motion and assuming a tunneling correlation time implemented from solving the Schrödinger equation. The acceptance of the tunneling correlation time resulting from the Schrödinger equation elucidates the reduction in the second moment at 0 K. The fitting leads to an excellent agreement between the experimental results of T1 temperature dependences a...