Two-dimensional n.m.r. characterization of cycloaliphatic epoxy resins

The cycloaliphatic epoxy resins were studied by various two-dimensional nuclear magnetic resonance (2D n.m.r.) spectroscopies. The ¹³C n.m.r. spectra of the epoxy resins were assigned by using DEPT and 2D INADEQUATE techniques and the ¹H n.m.r. spectra were assigned by using 2D ¹H---¹H and ¹H---¹³C COSY techniques. Complete characterization of the samples synthesized by the oxidation of cyclohexene derivatives not only revealed the existence of the stereochemical isomers resulting from the structural difference of the oxide rings in the samples but also provided the composition ratio of the isomers.     

Evaluation of a delayed coking process by H and C n.m.r. spectroscopy: 2. Detailed interpretation of liquid n.m.r. spectra

The ¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectra of a delayed coking feedstock and products, presented in a previous paper, are analysed here in detail by matching results from inspection of both nuclei. The conventional spectra of whole samples are used in combination with elemental analysis data, and substantial agreement is obtained. Differences are explored to yield valuable information. Interpretation of some band assignments is modified to account for new results. This approach results in a detailed quantitative estimation of a few key structures that contain the main functional groups that characterize these petroleum fractions.     

13C n.m.r. study of raw materials for carbon black

¹³C n.m.r. spectroscopy has been applied to investigate a number of coal tar and petroleum-derived carbon black feedstocks. Application of the J-modulated spin echo technique is especially rewarding, as this method renders the quaternary carbons directly detectable. Thus the quality of carbon black feedstocks can additionally be gauged on the basis of the contents of quaternary carbons, which is a direct indication of the carbon yield in the carbon black production process.     

Wide-line H n.m.r. study of perdeuterated pyridine imbibed in a premium coal

The motion of perdeuterated pyridine imbibed in Argonne premium high-volatile coal (no. 601) has been studied by wide-line ²H n.m.r. spectroscopy. The coal sample had been saturated with perdeuterated pyridine for several days, then evacuated until the pyridine reached a concentration of 3.5%. The entrapped pyridine molecules undergo two tyes of rotation about the twofold symmetry axis: rapid diffusional rotation with a correlation time of 1 × 10⁻⁷ s; and 180 ° jumps with a residence time of 6 × 10⁻⁶ s. It is estimated that roughly half of the pyridine molecules execute each kind of motion. There is no evidence for a pyridine fraction that executes rapid isotropic rotation. The anisotropic nature of the rotation indicates that the interaction between pyridine and the coal structure is strong enough to prevent isotropic rotation.     

Structural characterization of Saudi Arabian heavy crude oil by n.m.r. spectroscopy

Saudi Arabian heavy crude oil was separated into six fractions, including five distillate fractions (<93, 93–204, 204–260, 260–343 and 343–454 °C) and a >454 °C distillation residue. Each fraction was analysed by ¹H and ¹³C n.m.r. spectroscopy, and combined gained information from these analyses provided reliable average structural parameters. These included estimation of aliphatic and aromatic content, average paraffinic chain length, and estimation of hydrogen, methyl and alkyl bearing aromatic carbons for each of the six fractions. The extent of branching in paraffinic chains and amount of aromatic bridgehead carbons were also calculated.     

Application of lanthanide n.m.r. shift reagents for functional group studies of shale bitumen asphaltenes

Ytterbium (fod)₃ was used as a shift reagent in conjunction with solution ¹H n.m.r. studies of asphaltene isolated from Devonian shale bitumen. Upon addition of the reagent, bands attributed to protons on alkyl groups alpha to oxygen atoms were shifted and separated from that attributed to protons alpha to two aromatic systems. Similar experiments with Green River bitumen asphaltene did not show any observable shift. The presence and absence of the ether formations in shale asphaltenes can be substantiated by ¹³C n.m.r.     

C cross-polarization n.m.r. examination of the Glen Davis oil shale deposit

The use of solid-state ¹³C cross-polarization n.m.r. for rapid analysis of bore cores is demonstrated by examination of subsections of a Glen Davis oil shale bore. The determined aromaticities, f_a, differ widely between subsections indicating large variability in potential oil yields. The variation does not correlate with depth of subsection but is shown to correlate well with maceral composition. The correlation found previously by Zilm and co-workers (Fuel 1981, 60, 717) between f_a, determined by solid-state ¹³C n.m.r., and wt% fixed carbon for a range of macerals is found to be supported by the data for Glen Davis subsections which are mixtures of all three maceral types.     

Preliminary studies on the aromaticity of Australian coals: Solid state n.m.r. techniques

The aromaticities of samples from nine Australian coal seams, including pairs of hand-picked vitrains and durains, have been determined by ¹³C cross-polarization n.m.r. spectroscopy with magic angle sample spinning. The results clearly show that the aromaticity (f_a) of the coals increases with increase in vitrinite reflectance and carbon content and decrease in atomic H/C ratio. For a given coal seam, durain (inertinite-rich coal) has a higher f_a value than vitrain (vitrinite-tich coal). The trends for carbon content and atomic H/C are in good agreement with results from North American coals, although the aromaticities of Australian coals obtained in this study appear to be slightly lower than some of those reported for North American coals of similar carbon content.     

High temperature and high pressure H n.m.r. and e.s.r. studies on coal liquefaction reactions

Changes in chemical reactions during coal liquefaction of Yallourn brown coal and Akabira bituminous coal were monitored by using high temperature and high pressure ¹H n.m.r. A simple high temperature and high pressure e.s.r. cell was constructed and the variation in concentration of free radicals during coal liquefaction reactions was monitored under the same experimental conditions as for n.m.r. With the liquefaction and coking reaction, typical spectra of n.m.r. and e.s.r. were obtained and could distinguish the reaction steps: swelling; liquefaction; coking. The combination of high temperature and high pressure n.m.r. and e.s.r. is promising to the chemistry of coal liquefaction reactions.     

1H n.m.r. relaxation in bituminous coal and semicoke

Temperature and frequency-dependent proton relaxation measurements, in conjunction with spin concentrations determined by e.s.r., have shown that for fresh and oxidized coal the relaxation mechanism involves spin-diffusion to paramagnetic centres and to rotating methyl groups on alkyl chains. ¹H relaxation in semicokes is more complex; probably both direct relaxation to paramagnetic centres as well as spin-diffusion contribute.     

High resolution solid state C n.m.r. of Canadian peats

Peat samples from three locations in Quebec, Canada, were characterized by ¹³C CP/MAS n.m.r. spectroscopy. The n.m.r. analysis indicates that the peats contain a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes and resins. Integration of specific regions of the spectra can give semi-quantitative estimates of some of these plant components and, in limited cases, information about the degree of decomposition can be obtained from the ¹³C CP/MAS n.m.r. spectrum. Dipolar dephasing experiments and difference spectroscopy were found to be valuable techniques for spectra assignments and enhancement of compositional differences.     

Evaluation of the aromatic structure of coal tar pitch by solid and solution state n.m.r.

Rapid magic angle spinning has been used to obtain sideband-free high field ¹³C n.m.r. spectra of coal tar pitches in the solid state. However, the unfavourable cross-polarization and ¹H relaxation characteristics make it difficult to accurately estimate concentrations of quaternary aromatic carbon using the dipolar dephasing method. The concentrations of bridgehead aromatic carbon in the whole pitch and toluene-insoluble fraction investigated were deduced using a combination of solid and solution state n.m.r. and elemental analyses.     

A broad line n.m.r. study of oriented poly(vinylidene fluoride)

Broadline nuclear magnetic resonance measurements have been carried out for the proton resonance in oriented poly(vinylidene fluoride). The spectra in general show two component lines with distinctly different line widths. The broad component shows a high degree of molecular orientation and can be satisfactorily assigned to the crystalline regions of the polymer. The narrow component corresponds to an oriented non crystalline phase which is sufficiently constrained to allow motion about the chain axis only. An appreciable decrease in the value of the rigid mass fraction was observed in both of the samples over the temperature range examined. Our calculations indicate that this could play an important role in the temperature dependence of the pyroelectric response of this material.     

Estimation of aliphatic H/C ratios for coal liquefaction products by spin-echo 13C n.m.r.

The direct estimation of aliphatic H/C ratios for coal liquefaction products using a part-coupled spinecho (PCSE) ¹³C n.m.r. method is described. The method, which enables proportions of aliphatic C, CH, CH₂ and CH₃ groups to be deduced, has been applied to a low molecular weight (<200) aromatic fraction of hydrogenated anthracene oil (HAO) and to higher molecular weight (?280) aromatic and asphaltene fractions of supercritical gas (SCG) extracts and a hydrogenation residue (pitch). Aliphatic H/C ratios for these occur in the range 1.9-2.3, the SCG extract fractions having the highest values because they contain significantly more CH₃ and less CH than the HAO and pitch fractions.     

Structural analysis of Aleksinac oil shale kerogen by high-resolution solid-state C n.m.r. spectroscopy

A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state ¹³C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T_1C methods with a peak-synthesis technique applied to the ¹³C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain 79% long-chain aliphatic plus alicyclic structures, as well as 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.     

Quantitative solid-state C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Bloch decay or single pulse excitation (SPE) ¹³C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter ¹³C T₁'s of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter ¹³C T₁'s still result in observability of 75% of the carbon in the chars by the SPE technique. The ratios derived from the SPE measurements agree well with those obtained from elemental analysis.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

Structural characterization of Saudi Arabian medium crude oil by n.m.r. spectroscopy

Saudi Arabian medium crude oil has been characterized by ¹H and ¹³C n.m.r. spectroscopy. Several structural parameters such as the percentage of aliphatic carbons, aromatic carbons, n-alkanes, naphthenes, branched alkanes and chain length of paraffinic chains were calculated. The aromatic carbons were further classified as those attached to a hydrogen, methyl or alkyl group, or bridgehead carbons.     

Optimum conditions for high resolution C n.m.r. of coal- and oil-derived products

Factors affecting the spin-lattice relaxation times T₁ of ¹³C resonances at 62.9 MHz were investigated for simple mixtures of tetralin, ethylbenzene, pentane and phenol and the prominent resonances of an anthracene oil and a coal-derived hydrogenation oil. Parameters varied were solvent temperature and nature—Cr(acac)₃, Cr(dpm)₃, Cr(hfac)₃, Fe(acac)₃, Fe(dpm)₃—and concentration of a paramagnetic relaxation agent (PARR). Effects of PARRs on relaxation rates are strongly dependent on neighbouring acidic or basic centres, but are much more uniform for Cr(hfac)₃ than for Cr(acac)₃. The presence of basic or acidic compounds does not significantly affect the relaxation of ¹³C of the neutral components. Optimum experimental conditions are characterized by nearly uniform T₁ values of all resonances to be detected. While 2D spectra allow disentanglement of overlapping lines, choosing optimum conditions for the neutral constituents may lead to a loss of signals from the acidic or basic compounds.     

Monomer sequence determinations of aryl ether sulphone copolymers as determined by 13C n.m.r.

The monomer sequence distributions of three types of aryl ether sulphone copolymers have been determined by ¹³C n.m.r. spectroscopy. Two amorphous aryl ether sulphone copolymers were shown to have transetherified (or ether interchanged) during polymerisation to become random copolymers. The residues in these copolymers were (i)—OøOøSO₂øS—and (ii)—OøSO₂øøSO₂ø—-where ø denotes 1,4-phenylene. Copolymers of 50:50 aryl ether sulphone and aryl ether ketone made from different combinations of monomers were found to have different solubilities in dimethyl sulphoxide, and from ¹³C n.m.r. data this was shown to correlate with the amount of transetherification which had taken place during the polymerisations. The ¹³C n.m.r. chemical shifts for some of the carbon nuclei in these polymers were sensititive to functional groups situated even as far away as three or four aromatic nuclei along the polymer chain.