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Subject: search.filters.subject.530Author: search.filters.author.Schweitzer, DieterAuthor: search.filters.author.Haeberlen, UlrichInstitute: search.filters.UBSInstitut.Sonstige EinrichtungStart date: 1970End date: 1979

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Now showing 1 - 5 of 5
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    Nuclear magnetic shielding tensors for 1H, 13C, and 15N in organic solids
    (1975) Spiess, Hans Wolfgang; Haeberlen, Ulrich; Kempf, Jürgen; Schweitzer, Dieter
    A survey will be given of nuclear magnetic shielding tensors obtained by multiple pulse techniques for 1H in carboxylic acids and by high field NMR for 13C in carbonyl- and carboxyl groups of aromatic compounds and for 15N in pyridine and nitrobenzene.
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    13C nuclear magnetic relaxation studies at 62 MHz
    (1971) Jaeckle, H.; Haeberlen, Ulrich; Schweitzer, Dieter
    An apparatus suitable to measure 13C relaxation times T1 and T2 in liquids at 62 MHz is described. The required field of 58 kG is generated by a superconducting magnet. Results of T1 measurements on a variety of liquids, including benzene, derivatives of benzene, saturated rings, CS2, and others are reported. They are discussed in terms of dipole-dipole interactions, spin-rotation interactions and anisotropic chemical shifts, the latter of which turn out to play only a minor role. Intramolecular dipole-dipole interactions are found to provide by far the most important spin-lattice relaxation mechanism, whenever protons are bound directly to the carbons under investigation, even when the samples contain dissolved oxygen.
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    Spin rotation interaction and anisotropic chemical shift in 13CS2
    (1971) Spiess, Hans Wolfgang; Schweitzer, Dieter; Haeberlen, Ulrich; Hausser, Karl H.
    The 13C nuclear spin-lattice relaxation time T1 was studied in liquid CS2 from -106°C to +35°C at resonance frequencies of 14, 30, and 62 MHz. The relaxation is caused by anisotropic chemical shift and spin-rotation interaction. It is shown that for linear molecules the spin-rotation constant C and the anisotropy of the chemical shift Δσ can be obtained from the relaxation rates without use of adjustable parameters. The analysis yields: C = -13.8 ± 1.4 kHz and Δσ = 438 ± 44 ppm.
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    Molecular motion in liquid toluene from a study of 13C and 2D relaxation times
    (1973) Spiess, Hans Wolfgang; Schweitzer, Dieter; Haeberlen, Ulrich
    The 13C nuclear spin-lattice relaxation times for ring and methyl carbons in liquid toluene were studied from −95°C to +60°C at frequencies of 14 and 61 MHz. Data were taken for protonated as well as deuterated toluene. The results were analyzed in terms of three relaxation mechanisms: intramolecular dipole-dipole coupling, spin-rotation interaction, and anisotropic chemical shift. The last mechanism gives a significant contribution only to the relaxation rate of the ring carbons of the deuterated species at 61 MHz and low temperatures. A tentative value of Δσ = 295 ppm is obtained in this case. In order to separate the contributions of the dipole-dipole and spin-rotation interactions the 13C data are compared with deuteron relaxation times. Comparison of the 13C data in the protonated and deuterated form of toluene shows that the correlation times for the ring differ by 20% and an even larger effect of isotopic substitution is found for the methyl group. It is demonstrated that the fast internal motion of the methyl group cannot be studied quantitatively using deuteron or 13C intramolecular dipole-dipole relaxation rates alone because of the sensitivity of the results to the angle, varpi, the Z-axis of the electric field gradient, or the internuclear vector, respectively, forms with the C3 axis. Analysis of the relaxation rates due to spin-rotation interaction yields τj (internal), the correlation time of angular momentum of the internal motion directly. The correlation time of reorientation τc (internal) is calculated from τj (internal) using Gordon's extended diffusion model which is applied to a symmetric rotor with a fixed axis. It is found that both τj (internal) and τc (internal) are of the same magnitude as the correlation time of the free rotor. The ratio of correlation times of the overall and internal reorientation ranges from approximately 200 at the melting point to approximately 13 at +60°.
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    Spin echo experiments on 13C, 2H, 1H, and 19F in some small molecules in the liquid phase
    (1972) Haeberlen, Ulrich; Spiess, Hans Wolfgang; Schweitzer, Dieter
    The dependence on the π pulse repetition rate (2τ)−1 of the Carr-Purcell (CP) spin echo decay constant R is studied for four nuclei in C6H6, C6D6, C6F6, C6H12, C6H5CH3, CH3I, H2O, D2O, and CS2. Both deuteron resonances, the proton resonances of CH3I, of extremely pure H2O and C6H6 and the 13C resonance of CS2 yield straight lines when R is plotted vs. (2τ)2, i.e., R is governed by transverse relaxation and diffusion. However, in some unexpected cases, T2 is found to be smaller than T1. The H and F resonances of C6H6, C6F6, and H2O with traces of impurities do not give straight-line plots of R vs. (2τ)2. An oscillatory dependence of R on the pulse repetition rate is found for the 13C resonances of C6H6 and C6H5CH3. It can be shown to be due to the J coupling of the 13C spins to the directly bonded protons. The theory developed for exchange of chemically shifted spins can be applied and is extended for the slow exchange limit to an AX3 system in an effort to explain the results of methyl 13C quantitatively. Because of the sensitivity of CP measurements on instrumental effects a detailed description is given of the measurement procedures and of the equipment of which a superconducting solenoid is an essential part. A connection between Carr-Purcell measurements, of the Gill-Meiboom version, and spin-locking experiments is pointed out.