Joseph H. Noggle

13C and 35Cl NMR relaxation in liquid CCl4. A test of the extended J-diffusion model for molecular reorientation

Abstract Temperature dependent 13 C and 35 Cl NMR relaxation times in liquid CCl are used to derive values of both the reorientational and angular momentum correlation times τ θ,2 and τ J . The relationship found between τ θ,2 and τ J is in quantitative agreement with the extended J -diffusion model for molecular reorientation.

Carbon-13 spin-lattice relaxation in acetonitrile

Natural abundance 13C spin-lattice relaxation times and nuclear Overhauser effects are measured for acetonitrile between 239°K to 341°K at 2.114 T. Results are compared to other published relaxation data for this molecule and to various current relaxation theories. Dipole-dipole and spin-rotation relaxation are found to be important, but chemical shielding anisotrophy is not a significant mechanism at this field.

Rotating frame nuclear relaxation of PBr3: Off-resonance studies by fourier transform NMR

Abstract The theory for off resonance measurements of the nuclear spin-lattice relaxation time in the rotating coordinate frame (T1ϱ) is developed to facilitate measurements of this parameter by Fourier transform (FT) NMR. Measurements on PBr3 are used to test the theory, but the technique is developed so as to apply to multiline spectra suitable for FT-NMR study. Methods of interpreting data and applications are discussed.

23Na NMR studies of sodium ion interactions: Cysteine, aspartic acid, and citric acid

23Na nuclear magnetic resonance spin-lattice relaxation time measurements of aqueous sodium ion solutions containing cysteine, aspartic acid, and citric acid have been studied as a function of pH. Results indicate there is only a very weak interaction of cysteine and aspartic acid with sodium ion. Results with citric acid show that a sodium ion complex is formed with the citrate anion.

The calculation of nuclear overhauser effects in coupled spin systems

Abstract A theory and computational method are described for the calculation of selective nuclear Overhauser effects for scalar coupled nuclear spins. Sample calculations are included for three spins (two protons and one heteronucleus). The effect of rf power levels is described. Conclusions regarding the utility of selective nuclear Overhauser effects in structural chemistry are drawn.

Automated nonselective measurement of T1ρ by Fourier transform NMR

A simple, computer automated method for measuring rotating frame relaxation times (T1ρ) for many line spectra on modified commercial NMR spectrometers is discussed. Sources of error and critical instrumental parameters are identified. Adjustment of the various parameters of the pulsed rf system is more critical than for T1 but perhaps less so than for T2 measurements.

Nuclear magnetic relaxation of 31P in phosphorous halides

31P NMR spin–lattice relaxation time measurements in the laboratory frame, T1, and in the rotating coordinate frame, T1ρ, are reported for an equimolar mixture of PBr3 and PCl3. Relaxation times were measured as a function of temperature. T1ρ was measured also as a function of offset and lock‐field strength. The lock‐field dependent T1ρ technique is shown to be inadequate for exact determinations of scalar spin–spin coupling constants. We report for all four molecular species PBr3, PBr2Cl, PBrCl2, and PCl3 the following quantities: activation energies and frequency factors for chemical exchange and molecular reorientation and spin–lattice relaxation times for the bromines and chlorines. These quantities are obtained from the temperature dependent T1ρ measurements, which are shown to be suited for the study of chemical exchange processes when the exchange rates are in the order of 103–105 s−1. Using known values for quadrupolar coupling constants, we derive the temperature dependence of the reorientation c...