Robert I. McNeil

Benzylhexadecyldimethylammonium chloride in microemulsions and micelles

Abstract Several physical techniques have been used to study the nature and properties of benzylhexadecyldimethylammonium chloride micelles (BHDC), both as inverted micelles in benzene with aqueous cores, and as conventional “Hartley” micelles in water with hydrocarbon-like cores. For inverted micelles the nature of the water core or pool was investigated using IR spectroscopy, the absorption spectra of Co 2+ , and NMR spectroscopy. These data showed that the properties of bulk water were approached only when solvation of the surfactant ions was complete. The sizes of the micelles, both inverted and regular, were determined by a fluorescence technique. The data obtained for inverted micelles were in agreement with earlier measurements. The regular micelles in water were similar in size to micelles of cetyltrimethyl ammonium bromide (CTAB). Several laser-induced photoreactions also showed that the surface of a BHDC micelle was quite similar to that of CTAB. NMR data showed that the benzyl group of BHDC is directed toward the NCH 3 groups, and does not affect the physical processes studied. However, in inverted micelles the benzyl group is located toward the surfactant chain, and toward the bulk solvent benzene.

Hydrogen/deuterium transfer in coal liquefaction

Abstract Reactions have been made with deuterium-labelled solvent (d 4 - and d 12 -tetralin) and both Powhatan bituminous (Pittsburgh Seam) coal and model compounds under coal liquefaction conditions to study hydrogen transfer mechanisms. Powhatan coal liquefies quickly. Hydrogen transfer from the solvent to the reaction products continues throughout the heating period (up to 60 min). Significant hydrogen/deuterium exchange occurs and this strongly affects the distribution of deuterium in the products and also affects the extent of conversion as measured by the amount of THF-insoluble material. Increased deuteration of the solvent leads to decreased conversion. This exchange is enhanced by heavy aromatic species and by the presence of mineral matter and unconverted coal solids.

On the nature of surfactant vesicle and micelle systems

Abstract Several physical techniques, including fluorescence spectroscopy, laser photolysis, NMR, and electrical conduction were used to investigate the structural and kinetic properties of synthetic vesicles formed from didodecyldimethylammonium bromide. These structures are like their natural counterparts but unlike micelles in exhibiting broad lines in the proton NMR spectrum and in occluding glucose in their interiors, though diffusion through the vesicle walls is much more rapid than in the lecithins. The surface charge is low, with tighter binding of counterions such as I− and Br− than in micelles, and the head groups are in close proximity, both features typical of vesicles. The surface region appears to have a polarity much like that of cationic micelles, though the gradation to a nonpolar environment is much steeper in the vesicles. The vesicles modify photochemical reactions of species solubilized in these structures, in a fashion reminiscent of analogous micellar structures.

Interaction of lysophosphatidylcholine with phosphatidylcholine bilayers. A photo-physical and NMR study.

Several photo-physical methods together with 31P-NMR have been used to investigate the effect of lysophosphatidylcholine on phosphatidylcholine bilayers. 31P-NMR shows that the permeability of the vesicle to Eu3+ increases sharply above approx. 40% lysophosphatidylcholine: fluorescence-quenching studies also show this type of behavior. Similar sharp changes in vesicle properties are observed via the photo-physical technique at this lysophosphatidylcholine/phosphatidylcholine composition. Fluorescence spectra of pyrene and pyrene carboxaldehyde show that increasing lysophosphatidylcholine composition increases the polarity of the environments of these probes up to 40% lysocompound. Above this composition the photo-physical properties of the probes slowly revert to those characteristic of the micellar lyso-compound. The pyrene fluorescence lifetime, the fine structure of the fluorescence, and the case of formation of pyrene excimer in these bilayer mixtures suggest that pyrene complexes weakly with the charged nitrogen of the choline group of the phosphatidylcholine and that the physical state of the system has a striking effect on this complexation process. Similar experiments with simple quaternary compounds lend strong support to this suggestion. The studies monitor in several ways the effect of bilayer composition on movement of molecules in these systems. The degree or site of solubilization of carcinogens is also uniquely affected by composition.

The isotropic and anisotropic EPR spectra of the tetrafluoroethylene radical anion

Abstract The tetrafluoroethylene radical anion has been generated in solid solutions by electron addition to the parent molecule. Both its isotropic and anisotropic EPR spectra have been observed, including the isotropic 13C satellite lines in natural abundance. The isotropic EPR parameters are aF = 94.3 G, aC = 48.7 G, and g = 2.0027. Two possible geometries, planar and chair, are discussed for this radical anion. The magnitude of the 19F and 13C hyperfine coupling constants are consistent with a planar (D2h) structure provided that the unpaired electron occupies the 5b1u (σ*) rather than the 2b1g (π*) molecular orbital which is predicted by ab initio calculations to be the LUMO of the parent molecule. On the other hand, the EPR parameters do not rule out a chair (C2h) structure if the bending of the CF2 groups introduces only a small distortion from planarity.

Isomerization of tetra-hydroaromatic groups under coal liquefaction conditions

Abstract Model compound and coal liquefaction experiments have been carried out in a study of the isomerization of tetra-hydroaromatic groups in the solvent, a reaction which greatly reduces its hydrogen donor capability and limits the degree of upgrading of the coal-derived liquids. Major conclusions are: 1. (1) solvent isomerization of hydroaromatics cannot be prevented in that the reaction is due to the presence of free radicals, which cannot be avoided in coal liquefaction; 2. (2) the extent of the reaction at 450 °C indicates that the coal radicals have about the same selectivity in hydrogen abstraction as do benzyl radicals; 3. (3) mineral matter in coal does not appear to compound the problem by promoting the isomerization reaction; and 4. (4) the isomerized products are very stable under coal liquefaction conditions and, therefore, the build-up of methylindan-type structures is expected to be a problem in coal liquefaction processes.

Extents and models of adduction of hydrocarbon and nitrogen-containing solvents in coal liquefaction

Abstract Coal liquefaction experiments have been carried out to determine the tendency for adduction of several hydrocarbon- and nitrogen-containing structures typical of coal. Principal conclusions are: that even good hydrogen donors such as tetralin and octahydrophenanthrene are adducted readily; that benzyl radicals adduct primarily by radical-radical reaction, yielding thermally labile products; and that quinoline adducts to coal-derived liquids primarily by hydrogen bonding with little formation of C-C or C-N bonds.

EPR spectra and structure of the chlorotrifluoroethylene and bromotrifluoroethylene radical anions

Abstract EPR spectra attributable to the halogenotrifluoroethylene radical anions have been generated by electron attachment in solid solutions at low temperatures. The spin density distribution in these radicals strongly suggests that the unpaired electron occupies a σ* orbital, a conclusion which is supported by CNDO/2 calculations.

Novel cycloaddition of tetrafluoroethylene to the tetrafluoroethylene radical anion at 95 K: direct observation by EPR studies☆

Abstract The novel cycloaddition reaction C 2 F − 4 + C 2 F 4 ⇁ c -C 4 F − 8 has been observed directly by EPR spectroscopy in organic glasses at 80–95 K. According to the frontier orbital theory, the concerted reaction is symmetry allowed irrespective of whether the interaction is SOMOLUMO or SOMOHOMO, the SOMO of C 2 F − 4 being the 5b 1u (σ*) orbital suggested by EPR studies. The assignment of C 2 F − 4 as a σ radical also suggests that a concerted [2 + 2] suprafacial mechanism should be considered for the thermal cycloaddition reaction between two neutral C 2 F 4 molecules.

Predicting oil quality from sidewall cores using PFID, TEC, and NIR analytical techniques in sandstone reservoirs, Rio Del Rey Basin, Cameroon

Abstract The expense and uncertainty of obtaining fluid samples from MDT tools provide a strong incentive for an alternative method for assessing oil character. Sidewall cores, which are inexpensive and easy to obtain, contain sufficient oil for microanalyses that can provide indications of oil quality (degree of degradation), API gravity, and numerous additional characteristics, including sulfur content, acid number, and viscosity. The present study is concerned with the application of the micro-techniques PFID (pyrolysis-flame ionization detection), TEC (thermal extraction chromatography), and NIR (near infra-red spectroscopy) for the characterization of oil from sidewall cores taken from two exploration wells in the Rio Del Rey Basin of Cameroon in 1993.