No description available.

No description available.

No description available.

In the present study, interactions at the liquid/liquid and liquid/solid interfaces have been investigated by the combination of both nuclear magnetic resonance (NMR) and dynamic nuclear polarization (DNP) techniques. The ¹³C and ¹⁵N paramagnetic contact shifts, and ¹H, ¹³C, and ¹⁵N relaxation times in CH₃CN/2,2,6,6,-tetramethyl-1-piperidinyloxy (TEMPO) and CH₃CONH₂/TEMPO systems have been measured at high magnetic field (B₀ = 1.9-9.4 T). The 13 DNP enhancements at low magnetic field (0.33 T) in the CH₃CONH₂/TEMPO system have been determined by the flow liquid-liquid intermolecular transfer (LLIT) DNP technique. The data can be understood in terms of transient hydrogen bond formation between closed shell diamagnetic molecules and the open shell free radical TEMPO. A set of static and dynamic parameters, such as hyperfine coupling constants, correlation times, and free radicalnuclear internuclear distances in the hydrogen bonding complex, have also been determined. The scalar and dipolar contributions derived from the NMR study have been subsequently employed to predict the corresponding ¹H, ¹³C, and ¹⁵N low magnetic field (0. 33 T) DNP enhancements. Good agreement has been obtained between the NMR predicted and experimentally measured low magnetic field DNP results. The dynamic electron-nuclear intermolecular interactions between the newly discovered fullerene, C₆₀, and the free radical TEMPO have been characterized by flow LLIT and solid liquid intermolecular transfer (SLIT) DNP techniques. A dipolar dominated ultimate DNP enhancement (-250) at 0.33 T magnetic field has been observed. The results are consistent with a model for C₆₀/TEMPO interactions involving nonspecific complex formations. In addition to DNP studies in the liquid state, the solid/liquid surface intermolecular interactions in solid samples of various activated carbon specimens have been monitored by using flow SLIT 'H and ¹³C DNP experiments. The activated carbon samples were prepared by pyrolysis of cellulose, and commercial samples were also employed. The surface-liquid interaction in these studies were monitored with the solvent benzene ( or d₆-benzene). Both time dependent (Overhauser) and time-independent (solid-state) DNP enhancements were observed in these studies. Both chemisorption and physisorption processes of oxygen to the activated carbon were also monitored using the DNP approach. / Ph. D.

The use of ¹⁹F observation using MLEV ¹H decoupling in LC/¹⁹F {¹H} NMR was investigated as an alternative to LC/¹H NMR for fluorine containing mixtures and in order to avoid the solvent background problems associated with LC/¹H NMR. P-fluorobenzoate derivatives of various alcohols were analyzed by both LC/¹⁹F {¹H} and LC/¹H NMR. Another alternative exists in supercritical fluid chromatography. A delivery system was assembled and an NMR flow probe was developed and demonstrated practical for directly coupled SFC/¹H NM. The alkane substituents of a model fuel mixture were identified using SFC/¹H NMR in contrast to using the normal phase LC/¹H NMR approach. The relaxation behavior and molecular motion of dilute solutions of benzene and acetonitrile in sub- and supercritical CO₂ were determined using stopped flow ¹H and ¹⁴N NM. The nuclear spin-lattice relaxation times (T₁) for ¹H and ¹⁴N were measured through inversion recovery and linewidth, respectively. Relaxation was found to be dominated by spin-rotation interactions with molecular correlation times (r_sr and _rc) being determined directly from the ¹H and ¹⁴N T₁ over a wide range of viscosities and temperatures. Line-narrowing improvements of ¹⁴N averaged 3-fold as a result of the increased molecular motion. The increased molecular motion as a result of supercritical CO₂ resulted in improved signal enhancement using flow dynamic nuclear polarization. The observed enhancements were two times greater than that typically achieved for the same system and configuration using normal liquid solutions. Through observed NMR enhancements, relative microwave magnetic field values in the vicinity of the NMR coils were measured for typical flow and static DNP-NMR configurations. The advantages of the former were noted. / Ph. D.

A method has been developed whereby various physical properties of middle distillate fuels may be rapidly and accurately calculated by a group property approach from data obtained from a directly coupled Liquid Chromatograph -⁻¹H Nuclear Magnetic Resonance Spectrometer (LC-⁻¹H NMR). The physical properties include cetane number, cetane index, density, specific gravity, pour point, flash point, viscosity, filterability, heat of combustion, cloud point, volume percent aromatics, residual carbon content, and initial, 10%, 50%, 90%, and end boiling points. These property predictions have accuracies approaching the error for measurement of the experimental physical property and require less than two hours analysis time per fuel. An interface was developed between the NMR spectrometer and a personal computer to aid in automation of the LC-⁻¹H NMR data collection and to perform off-line analysis of the LC·⁻¹H NMR data. This interface and all associated software is described. Also presented is a series of model compound studies in which the physical properties of pure hydrocarbons (i.e., alkanes, monocyclic and dicyclic aromatics) were predicted by a similar group property approach. / Ph. D.

The intramolecular carbonyl exchange which occurs in solution for the dinuclear and tetranuclear cobalt complexes containing the bisphosphines DPM, bis(diphenylphosphino)methane; DMPM, (dimethyl-diphenylphosphino)methane; and DMM, bis(dimethylphosphino)methane is very fast at temperatures down to -80°C. For the tetranuclear clusters Co₄(CO)₈(DPM)₂, Co₄(CO)₈(DMPM)₂, Co₄(CO)₈(DMM)₂, and Rh₄(CO)₈(DPM)₂, this exchange is slow at -80°C on the NMR time scale. The postulated mechanism for carbonyl exchange is based on a previously proposed mechanism, which is the expansion of the ligand icosahedron into a cubooctohedron. Because of the constraints imposed by the bisphosphine ligands, only one ligand icosahedron can be formed that is consistent with the known structure. Racemization of enantiomers by rotation of the ligands on the apical metal atom can occur, and thus enables complete carbonyl exchange to take place. The series of binary metal carbonyls: Co₄(CO)₈, Fe₃(CO)₁₂, Co₄(CO)₁₂, Co₃Rh(CO)₁₂, Co₂Rh₂(CO)₁₂ and Rh₄(CO)₁₂, has been studied by variable temperature MAS (magic angle spinning) ¹³C NMR spectroscopy. All of these molecules except for Rh₄(CO)₁₂ show dynamic behavior as evidenced by their solid state ¹³C NMR spectra. Since carbonyl ligands cannot move within the crystalline lattice to an extent sufficient to render bridging and terminal carbonyls equivalent, then the dynamic behavior observed for the binary metal carbonyls must be described as metal atom movement within the carbonyl cage. The tetranuclear clusters which contain rhodium show a higher coalescence temperature in their NMR spectra than Co₄(CO)₁₂. As the rhodium content increases the activation energy for carbonyl exchange for exchange increases. cluster Rh₄(CO)₁₂ does not exhibit dynamic behavior in the solid state. lt is concluded that the rhodium tetrahedron is too large to move within the carbonyl cage. The cobalt “A-Frame" complexes Co₂(CO)₃,(DPM)₂I₂, Co₂(CO)₃(DMM)(DPM)I₂, and Co₂(CO)₃(DPM)₂S were synthesized but show no dynamic behavior in solution. The crystal structure of Co₂(CO)₃(DMM)(DPM)l₂, shows that this "A-Frame" complex is coordinatively saturated around the cobalt atoms. Thus, these molecules are relatively inert, and show no evidence of carbonyl scrambling. / Ph. D. / incomplete_metadata

The use of proton nuclear magnetic resonance (NMR) spectroscopy as an on-line continuous flow detector for liquid chromatography (LC-¹H NMR) is described. Flow inserts for electromagnet and superconducting solenoid magnets are described. Applications to fuel analysis are presented. LC-¹H NMR is shown to be an informative technique. The principle limitation is sensitivity. Conditions for quantitative flow pulse NMR measurements are presented. An average composition method for fuel samples (based on LC-¹H NMR) is derived. This method is shown to be of value in characterizing the aromatic fractions of low boiling fuels. Average degrees of substitution, number average molecular weights, and other quantities can be determined with this method. A theoretical description of flow NMR experiments is developed. The classical description of magnetization (based on the Bloch equations) and detailed physical pictures of flow are combined in computer simulations. Several examples are given and computer program listings are appended. / Ph. D.

This paper describes a new technique for analyzing fire debris using nuclear magnetic resonance (NMR) spectroscopy. Petroleum distillates, which are commonly used accelerants, were weathered, burned, and steamdistilled. These, as well as virgin samples of the accelerants, were analyzed by gas chromatography and nuclear magnetic resonance spectroscopy. In addition, solvent studies and detectibility limit studies were conducted. The use of NMR is described as a valuable adjunct to the existing methods of analysis.

No description available.