Nuclear Magnetic Resonance Absorption Research Articles

A new method for the study of molecular rearrangements with the use of carbon-13 double resonance NMR spectra

Carbon-13 nuclear magnetic double resonance absorption spectra with complete decoupling of hydrogen nuclie has been used to established the rearrangement by hydride ion shifts of the cyclohexyl cation in the formolysis reaction of cyclopentacarbinyl- 13C p-toluenesulfonate

Proton magnetic resonance absorption of halomethane “guest” molecules in clathrate hydrates

With a view to obtaining information on the nature and extent of molecular motion of enclathrated “guests” and their interaction with the “host” lattices, the nuclear magnetic resonance absorption of four halomethanes included in the clathration voids of fully-deuterated hydrates has been studied from 77°K. upwards. For the three monohalomethanes (CH 3X; X = Cl, Br, I) the low-temperature proton resonance results indicate constraints to reorientational and translational motion inside hydrate host cavities. A triplet line-shape has been observed for the CH 3Br-clathrate at 77°K. At higher temperatures, expansion of the deuterium-bonded hydrate lattices has been proposed, which permits free C 3-reorientations of the CH 3 groups of the guest molecules. From the associated linewidth transitions, activation energies of 2.48±0.32, 9.30±0.25, and 6.80±0.50 kcal mole −1 have been calculated for the potential barrier hindering methyl reorientation in the CH 3Cl-, CH 3Br- and CH 3I-clathrates, respectively. The motional model proposed is supported by measurements of the 1H spin-lattice relaxation times.

Physical studies of phospholipids VIII. Nuclear magnetic resonance studies of diacyl- l-phosphatidylcholines (lecithins)

Proton magnetic resonance spectra of anhydrous polycrystalline 1,2-distearoyl-phosphatidylcholine (lecithin) have been obtained at temperatures between 196° and 150°. The decrease of line width and second moment with increasing temperature indicates increasing rates and amplitudes of reorientation up to a sharp transition point. The motion is probably rotatory and oscillatory in nature, but with a wide distribution of correlation frequencies. The mesomorphic phase above the transition gives a narrow nuclear magnetic resonance absorption line corresponding with rapid molecular reorientation which is not isotropic. Similar spectra are found for egg yolk lecithin, and the discussion of molecular motion in phospholipids may therefore be relevant for the reorientations of many lipids in biological membranes. Preliminary studies of the influence of water ( 2H 2O) on the molecular motion of phospholipids are also described.

Nuclear Magnetic Resonance Absorption in Metals in the Region of the Doppler-Shifted Cyclotron Edge

A calculation has been made of the nuclear magnetic resonance lineshape in a semi-infinite metal slab with a magnetic field perpendicular to the sample surface. The range of frequencies has been chosen such that the resonance moves from below the Doppler-shifted cyclotron edge to above it. A discussion of the feasibility of such an experiment is given.

Magnetic Resonance Study of Molecular Motion in Cubic (NH4)2SiF6

Proton, fluorine, and deuteron magnetic resonance absorption line shapes, as well as 1H and 19F spin—lattice relaxation times, have been measured in polycrystalline cubic (NH4)2SiF6 and (ND4)2SiF6 from −170° to +100°C. The results demonstrate that the threefold proton disorder in the NH4 groups is indeed dynamic and not static, and suggest the following mode of reorientation: The NH4 tetrahedron is first excited from the ground torsional—vibrational state to nearly continuous levels above the potential barrier, and after a short interval of nearly free rotation again drops to one of the three possible equilibrium orientations in the ground state. On the average, each proton spends the same amount of time in each of the 12 equilibrium sites. Large-amplitude rotational oscilations in the ground state are also consistent with the experimental data. The existence of a 19F linewidth transition, as well as spin—lattice relaxation data, demonstrate the onset of hindered rotation of the SiF6 ions above room temperature.

Characterization of polystyrenes of controlled molecular weight by nuclear magnetic resonance spectroscopy

The linewidths (δH) of proton magnetic resonance absorption spectra of polystyrenes of “controlled” molecular weight in the range 10,300 to 860,000 have been studied as a function of temperature in the range 100° to 420°K. The results of this study, together with the derived parameters, such as the activation energy (ΔE) for various reorientations of the polymer chain and the glass transition temperature (Tg), have been shown to provide sensitive criteria for characterizing these polymers. The Tg values are compared with those obtained by other workers using dilatometric techniques. The variation of Tg and ΔE with other parameters and some aspects of the dielectric and N. M. R. relaxation relative to certain molecular reorientations are discussed.

Proton Magnetic Resonance of Solid 1,1,1,2-Tetrachloro-2-methylpropane

Abstract The molecular motion in the crystal lattice of 1, 1, 1, 2-tetrachloro-2-methylpropane was studied, by proton magnetic resonance absorption measurements, over the temperature range between 30°C and −190°C. The absorption-line witdhs changed at −62°C. The second moments remain almost constant, about 5 gauss2, between from −63°C to about −150°C, whereas above −62°C the values fall suddenly to 0.5 gauss2. From the analysis of the proton second moment, it was found that, in the high-temperature phase, the molecules rotate almost freely in the crystal lattice, while in the low-temperature phase, the major molecular motion is the rotation of the methyl groups about the C–CH3 bonds in the molecule.

Equilibrium constants of charge-transfer complexes determined from 19F nuclear magnetic resonance absorption measurements

Measurements of the line position of 19F nuclear magnetic resonance absorptions of 2,3,5,6-tetrafluoro-p-benzoquinone (fluoranil) and of 1,4-dicyano-2,3,5,6-tetrafluorobenzene in the presence of various concentrations of methylbenzenes have been made. These observations have enabled the equilibrium constants for the appropriate electron-donor–acceptor complexes to be calculated. The results show the expected increase in stability in the two series of complexes with increasing methylation of the electron-donor molecule. Fluoranil forms stronger complexes than 1,4-dicyano-2,3,5,6-tetrafluorobenzene. The complexing ability of the latter is about equal to that of 1,3,5-trinitrobenzene. For a given complex, the association constant decreases as the solvent is altered in the series carbon tetrachloride, chloroform, 1,2-dichloroethane-dichloromethane. For the series of methylbenzene–fluoranil complexes in carbon tetrachloride, the chemical shift of the fluorine nuclear magnetic resonance in the complex, relative to the chemical shift in uncomplexed fluoranil, increases as the stability of the complex increases. These values of equilibrium constant have been used to recalculate the molar extinction coefficients of some complexes.

Fluorine magnetic resonance of solid chloropentafluorobenzene

The nuclear magnetic resonance absorption spectrum of solid chloropentafluorobenzene has been studied at temperatures between 77 °K and the melting point. The experimental values of the second moment have been divided into two parts, one due to broadening by nuclear dipole-dipole interactions and the other due to broadening by the anisotropy of the fluorine chemical shift. The absorption line begins to narrow at 190 °K, close to the temperature of a specific heat anomaly. Consideration of the effects of molecular motion on both parts of the second moment show that the narrowing is due to rotation about an axis perpendicular to the plane of the molecule.

Enhancement of Nuclear Magnetic Resonance in Bulk Rubidium in the Size-Effect Regime

The intensity of nuclear magnetic resonance absorption of ${\mathrm{Rb}}^{87}$ nuclei in a thin slab of purified, cooled metal is observed to increase significantly in the range of magnetic-field strength and orientation where nearly sinusoidal size-effect variations in the surface resistance are found. Though no quantitative description of the effect is presently available, it clearly results from enhanced penetration of radio-frequency currents and fields into the bulk of the metal slab due to the cyclotron motion of the electrons. The phenomenon is expected to be generally observable in pure metals at low temperatures.

Physical Chemistry of Binary Plastic Crystals. I. The System of Carbon Tetrachloride and t-Butyl Iodide

Abstract The binary system, carbon tetrachloride- t-butyl iodide, was studied by the proton magnetic resonance, the dielectric measurements and the X-ray diffraction. The complete phase diagram, constructed by the differential thermal analysis, shows a solid solution region where carbon tetrachloride is more than 50 mole%. Detailed studies of the solid solution containing 6.6 mole% of t-butyl iodide reveals that the solution can be described by the theory of regular solutions; its molecular polarization above the transition temperature obeys the Debye formula giving the dipole moment of t-butyl iodide a value of 1.6 debye units. The high-resolution nuclear magnetic resonance experiments with the same phase shows that carbon tetrachloride molecules diffuse in the solid solution with an energy of activation of 6.8 kcal./mole. The transition temperature varies with the composition, and below it the rotational motion of the solute molecules is more hindered. Pure t-butyl iodide shows motional narrowing around –150°C in the NMR line shape, above which temperature a reorienting molecular model can account for the magnitude of second moment of the nuclear magnetic resonance absorption.

Liquid water in frozen tissue: study by nuclear magnetic resonance.

Nuclear magnetic resonance (NMR) spectroscopy was used to examine the behavior and extent of liquid water in postrigor-frozen tissue of cod at temperatures below 0 degrees C. A liquid-water phase persists in the tissue down to about -70 degrees C; the extent of the phase decreases rapidly between 0 degrees and -10 degrees C and slowly at lower temperatures. That the NMR absorption peak of the liquid water increases in width, with decreasing temperature, suggests loss of mobility or structuring of the phase. A technique for introducing geometrically uniform cores of muscle into the probe of the high-resolution spectrometer permits quantitative determinations of liquid water.

Addition reactions of heterocyclic compounds. Part XXV. Dimethyl acetylenedicarboxylate with pyridazines and pyrazines

Dimethyl acetylenedicarboxylate in acetonitrile with pyridazine, 3-methylpyridazine, and 1-methylphthalazine gave pyrido[1,2-b]pyridazines, with smaller amounts of related pyrrolo[1,2-b]pyridazines. 3,6-Dimethylpyridazine, however, gave mostly an azepino[1,2-b]pyridazine. 2-Methyl- and 2,6-dimethyl-pyrazines gave only low yields of pyrrolo[1,2-a]pyrazines under these conditions. In methanol, phthalazine gave 1,2-dihydro-1-methoxy-2-(1,2-dimethoxycarbonylvinyl)phthalazine, and phenazine gave 5,10-dihydro-5,10-di-(1,2-dimethoxycarbonylvinyl)phenazine. The nuclear magnetic resonance and ultraviolet absorption spectra of these adducts and their transformation products are discussed.

Nuclear Magnetic Resonance Absorption in Anhydrous Sodium Soaps

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNuclear Magnetic Resonance Absorption in Anhydrous Sodium SoapsKenneth D. Lawson and Thomas J. FlauttCite this: J. Phys. Chem. 1965, 69, 12, 4256–4268Publication Date (Print):December 1, 1965Publication History Published online1 May 2002Published inissue 1 December 1965https://doi.org/10.1021/j100782a032RIGHTS & PERMISSIONSArticle Views73Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Nuclear magnetic resonance spin-spin relaxation

A general method is described for the calculation of the relaxation function G(t) for a macroscopic nuclear magnetization perpendicular to a strong steady magnetic field, under the influence of the nuclear dipole-dipole interaction. This function is the Fourier transform of the nuclear magnetic resonance absorption line shape. Approximations are introduced, the form of which depends upon whether the short-term or the long-term development of G(t) is required. A third type of approximation leads to the equation of Lowe and Norberg. The theory is applied to the case of the fluorine resonance in calcium fluoride with the steady field in the [100] direction. The first approximation gives a curve that differs only slightly from that of Lowe and Norberg over the range of t for which the latter is in good agreement with experiment. For larger t the disagreement with experiment is less severe, the characteristic oscillation of G(t) being present, though with too large an amplitude. In contrast the second approximation gives a curve which though overdamped provides a better description of the approach of the spin system to equilibrium. The theory may be extended to problems in which the dipolar Hamiltonian possesses an explicit time dependence. In this form it is applied to the case of motional narrowing due to rapid rotation of the sample about an axis inclined at 54.7° to the magnetic field, for which the absorption spectrum consists of a narrow central line flanked by an infinite series of sidebands spaced at intervals corresponding to the rotation frequency. It leads to a separation of the two components of the second moment of the spectrum due respectively to the generation of sidebands and to the finite width of the lines. Though the sum of these contributions is invariant to rotation they themselves are not. An assumed form for the shape of the lines leads to a linewidth which for rapid rotation depends inversely on the cube of the rotation frequency and is in substantial agreement with an earlier statistical theory.

Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions1

Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions¹

ISOLATION AND CHARACTERIZATION OF A NEW ANTIBIOTIC, ABBOTT 29119, FROM STREPTOMYCES ERYTHREUS.

A new antibiotic was isolated from fermentations of Streptomyces erythreus designed for erythromycin A production. Isolation of this compound was accomplished by use of ion-exchange chromatography and countercurrent distribution. It crystallized from methyl isobutyl ketone in colorless acicular plates which melted at 127 to 130 C. The empirical formula was C(42)H(75)NO(14) with a molecular weight of 820. Electrometric titration in 66% dimethylformamide showed an apparent pKa of 8.4. Nuclear magnetic resonance, infrared, and ultraviolet absorption indicated a close resemblance of the compound to known erythromycins, although its chromatographic behavior and solubility differed from those of the known erythromycins. Its antimicrobial spectrum was similar to erythromycin A, but the minimal inhibitory concentrations were much higher.

Pressure Dependence of the Internal Field at the 59Co Nucleus in a 99.5% Ni-0.5% Co Alloy

The room-temperature nuclear magnetic resonance absorption of 59Co in an alloy of 0.5% Co in Ni has been measured under hydrostatic pressures of up to 7 kbars. The change in the resonance frequency with pressure is Δv/Δp=159±5 Hz/bar. This is in the same direction (increasing frequency for increasing pressure) as for 61Ni in Ni. The ratio of the resonance frequency at absolute zero to the change in frequency with pressure v0: Δv/Δp is 750 kbar for 59Co and 1200 kbar for 61Ni in Ni. The internal field at the 59Co nucleus decreases with increasing temperature more slowly than that at the 61Ni nucleus in Ni-rich Ni-Co alloys. This discrepancy in the temperature dependences remains as large, when plotted at constant volume, as it was at constant pressure.

Nuclear Magnetic Resonance Study of Molecular Motion in Polyethylene Crystal

An NMR (nuclear magnetic resonance) study is made on the α or crystalline dispersion of polyethylene which has been found viscoelastically between room temperature and its melting point. Narrowing of NMR absorption line, increase of the mobile fraction and anisotropy of the narrowing are observed in the temperature range of the α dispersion both on melt grown and solution grown specimens. This α narrowing is found to occur at higher temperatures (i.e. the relaxation time is longer) for specimen with thicker crystalline lamella and to be so anisotropic that it disappears when all the molecular axes are aligned parallel to the main magnetic field H0. The experimental results indicate that the molecular motion underlying the crystalline dispersion is the large amplitude torsional oscillation of folded polyethylene chains.

Dynamic nuclear polarization in crystals

We shall be concerned with a system of nuclear spins in coupling with electron spins in a solid, and the possibility of polarizing appreciably the nuclear spins through excitation of the magnetic resonances of the system. This is another example of a dynamic polarization method, but in contrast to the cases just discussed by Professor Abragam and Professor Richards, the nuclei are polarized directly by inducing certain forbidden microwave transitions (Jeffries 1957, 1960). After a rather general description of the phenomena, directed toward those unfamiliar with these methods, details will be given with applications to polarized proton targets. To fix ideas, think of a single crystal of the double nitrate La 2 Mg 3 (NO 3 ) 12 . 24H 2 O, in which, say 1% of the La 3+ ions have been replaced by paramagnetic Nd 3+ ions, which are our electron spin system. The nuclear spins may be either the Nd nuclei; or the nuclei H, La, N, etc., in neighbouring diamagnetic atoms. We consider these cases separately below. Imagine the crystal to be enclosed in a copper box, i. e. a microwave cavity, immersed in liquid helium at T ~ 1 °K and in a magnetic field H ~ 10 4 G. Figure 32 shows the experimental arrangement to keep in mind. An r. f. coil wound around the crystal may be used for measuring the nuclear magnetic resonance absorption, which is just proportional to the nuclear polarization.