D.s.c., electrical conductivity,and n.m.r. studies of salt precipitation effects in PPO complexes

Differential scanning calorimetry (d.s.c.) and electrical conductivity measurements of poly(propylene oxide), PPO, complexed with the salts NaI and KSCN are reported. In addition, ²³Na n.m.r. measurements on PPO-NaI (x = 8), both at ambient and elevated pressure (2 kbar), have been performed. The d.s.c. data clearly indicate that the salt precipitates out of the complexes at about 85°C for NaI and 60°C for KSCN. These effects are manifested by a dramatic departure of the conductivity from Vogel-Tammann-Fulcher (VTF) behaviour, and a relatively sharp drop in mobile Na⁺ concentration, as deduced from n.m.r. measurements, above about 80°C. High pressure n.m.r. linewidth measurements are consistent with a pressure-induced increase in glass transition temperature.     

Oil-shale analysis by CP/MAS-13C n.m.r. spectroscopy

Solid-state ¹³C n.m.r. (CP/MAS-¹³C n.m.r.) spectroscopy provides a direct method for estimating potential oil yields of oil shale formations. Relative aliphatic resonance areas correlate linearly with oil yield and provide a method for oil yield estimation that obviates the need to determine weight per cent organic carbon for each specimen. This direct measurement is performed using an internal area standard, the carbonyl resonance of N-(2-¹³C-propanonyl)-N,N,N-trimethylammonium chloride, to monitor spectrometer sensitivity. Oil shale samples obtained as a function of depth at a site in the Mahogany Zone of the Green River Formation show a near-constant aliphatic carbon fraction, f_al ≡ (1?f_a), and a twofold, nonlinear variation in oil yield over the vertical dimension of the sampling. Aliphatic carbon resonance band shape changes among these samples are interpreted qualitatively as reflecting a two component mixture composed of the condensed alicyclic structures which link together to form the kerogen matrix and an n.m.r.-distinct but not necessarily chemically distinct contribution from normal-long chain hydrocarbon residues.     

Characterisation of some melamine-formaldehyde condensates and some cured resins by 1H, 13C and 15N n.m.r. spectroscopy

Some oligomeric species (condensates) in a melamine-formaldehyde adduct mixture have been isolated by preparative high performance liquid chromatography (h.p.l.c.) and partly identified by high field ¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectroscopy. The oligomers are shown most likely to be largely dimers, trimers and tetramers and to contain both methylene and methylene ether linkages. Some cured melamine-formaldehyde resins are shown by solid-state cross-polarisation magic angle sample spinning (c.p./m.a.s.) ¹³C and ¹⁵N n.m.r. to contain linear and branched methylene and methylene ether linkages but few free methylol groups. The relative proportions of the various linkages in both the oligomers and the cured resins appear to be controlled mainly by the melamine: formaldehyde ratio.     

Quantitative estimation of CHn group abundances in fossil fuel materials using 13C n.m.r. methods

Comments on the use and relative merits of gated spin echo (GASPE) and spin echo broad band off-resonance decoupling (SEBBORD) selected multiplet ¹³C n.m.r. methods, for the identification and quantitation of CH_n (n = Q?3) groups in fossil fuel materials, are given in response to recently published reports.     

Dynamic structure of swollen crosslinked poly(ethylene oxide) gels from n.m.r. line-shape analysis and magic angle rotation n.m.r.

Chemically crosslinked poly(ethylene oxide) gels swollen to equilibrium in CDCl₃ (22.3 w/w% of polymer) and CCl₄ (77.5 w/w% of polymer) were characterized by combination of the results of ¹H n.m.r. spectra measured with magic angle rotation (MAR-n.m.r.) and numerical analysis of static ¹H n.m.r. line shapes. From MAR-n.m.r., activation energies of rapid segmental motions were found to be 1.7 ± 0.3 kcal mol^?1 in CDCl₃ and 9.4 ± 0.6 kcal mol^?1 in CCl₄. Static line-shape analysis yields a parameter which characterizes the deviation of segmental motions from isotropy in space. This parameter was found to be independent of temperature and equal in both systems.     

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.     

Investigation of aromatic carbon sites in materials derived from petroleum and coal using 13C n.m.r. methods

Aromatic C and CH carbon sites in a variety of petroleum and coal derived materials have been investigated using a ¹³C n.m.r. technique termed spin echo broad band off-resonance decoupling (SEBBORD). Only resonances due to non-protonated aromatic carbon sites are observed in SEBBORD spectra such that comparison with conventional ¹³C n.m.r. spectra enables differentiation between aromatic C and CH group resonances. Relative abundances of non-protonated aromatic carbon sites calculated from SEBBORD data are in good agreement with values derived from a combination of conventional¹H n.m.r., ¹³C n.m.r. and elemental analysis data. The occurrence of significant proportions of aromatic C intensity to high field of 129–130 ppm and of aromatic CH intensity to low field of 129–130 ppm has been found to be quite common. Consequently attempts to determine aromatic C and CH group abundances by partitioning conventional ¹³C n.m.r. spectra in the vicinity of 129–130 ppm can lead to considerable quantitative errors. SEBBORD provides more detailed information about aromatic carbon sites than can be obtained from conventional ¹³C n.m.r. spectra.     

Characterisation of separated melamine—formaldehyde adducts (methylolmelamines) and adduct mixtures by h.p.l.c. and by n.m.r. and u.v. spectroscopy

Most of the individual methylolmelamines that occur in melamine–formaldehyde adduct mixtures have been separated by preparative high-performance liquid chromatography (h.p.l.c.) and recovered in amounts sufficient to allow their characterisation by high-field ¹H- and ¹³C-n.m.r. Particular attention has been paid to the chemical shifts of the aromatic azine carbons of the melamine nuclei. These carbon shifts are shown broadly to be in agreement with some values previously published, but additional assignments have been made. It is shown that a satisfactory quantitative analysis of the methylolmelamines in a melamine–formaldehyde adduct mixture can be carried out either by h.p.l.c. or by ¹³C-n.m.r.     

Quantitative FT 13C n.m.r. of solvent-refined coals using sym-triazine as solvent

Aromaticities (f_a) determined for several solvent-refined coals (SRC) by ¹³C n.m.r. in sym-triazine solution and by the Brown and Ladner ¹H n.m.r. technique have been found to be the same within experimental error (0.01). Use of sym-triazine to determine the f_a of the soluble and insoluble fractions of a SRC in several solvents showed that the soluble fraction reflected reasonably accurately the properties of the whole sample for dioxan, carbon disulphide, chloroform and benzene extracts. The properties of the insoluble fraction varied only slightly. A more detailed analysis of the aromatic region of the ¹³C n.m.r. spectrum has led to some useful structural relations.     

Nuclear magnetic resonance studies on sequence distributions in vinyl alcohol-vinyl acetate copolymers

The microstructure of vinyl alcohol-vinyl acetate copolymers was studied using both ¹³C n.m.r. and ¹H n.m.r. techniques. The sequence lengths of vinyl acetate units calculated respectively from the compositional dyads, from the methylene absorptions and feom the triple carbonyl absorptions in the ¹³C n.m.r. spectrum were not identical, and moreover the dyad-triad relationship showed a large discrepancy. ¹H and ¹³C n.m.r. spectra of a 5 mol% re-acetylated random sample, containing mainly isolated acetate units, indicate that configurational splitting complicates the assignment of the triple carbonyl absorption, which originally was interpreted as a compositional triad. After correcting for tacticities the results could be brought in line and the C=O resonances proved to be useful in obtaining information on the percentage of isolated vinyl acetate units and the sequence length n^A₂₊ (the average length of vinyl acetate units ≥2).     

1H n.m.r. technique for characterization of polymerized petroleum pitches

A new proton n.m.r. technique has been developed for the chemical characterization of polymerized petroleum pitches with pyridine-insoluble contents as high as 80%. The polymerized pitches were completely solubilized for conventional ¹H n.m.r. evaluation in a mixed solvent system consisting of S₂Cl₂-SO₂Cl₂. Although solubilization occurs via the addition of chlorine to the polynuclear aromatic rings, the n.m.r. spectra can still be quantitatively interpreted. Several applications are discussed.     

An investigation of coal by means of e.s.r., 1H n.m.r., 13C n.m.r. and dynamic nuclear polarization

Sixty coal samples of different rank and origin have been investigated by means of e.s.r., ¹H n.m.r. and ¹³C n.m.r., the last two in combination with dynamic nuclear polarization (DNP). The following parameters have been determined: the number of free radicals, the e.s.r. linewidth, the ¹H Zeeman relaxation rate, the ¹H relaxation rate in the rotating frame, the ¹H DNP enhancement, the ¹³C DNP enhancement, the ¹³C Zeeman relaxation rate and the ¹³C aromaticity, observed via ¹H¹³C cross-polarization (CP), both with and without magic-angle spinning (MAS). The relations between these parameters and coal rank have been investigated. Moreover, with DNP special experiments have been performed which provide information about the localization and the mobility of the unpaired electrons present in these coals. Finally, DNP has been used to investigate various features of the quantitative analysis of coal via ¹³C n.m.r. MAS was found to reduce the measured ¹³C aromaticity, and for three coals it was shown that even without MAS only ≈ 50% of the aromatic ¹³C nuclei are detected by the CP technique.     

Liquefaction reaction of coal: 2. Structural correlation between coal and its liquefaction products

The structural correlation between coal and its liquefaction products has been examined using cross-polarization, magic angle spinning (CP/MAS) ¹³C n.m.r. and field ionization mass spectrometry (f.i.m.s.). The CH₂/aromatic carbon ratios of all solid products (asphaltene, preasphaltene and residue) were close to the corrected +CH₂/aromatic carbon ratio for the coal. This suggests that the ring structure of the structural unit of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. The CH₂/aromatic carbon ratios of aromatic ring-type oil fractions also correlated with the corrected ratio for the coal, although they were larger. The z series distribution obtained from the f.i.m.s. of oil fractions revealed that coal with a higher CH₂/aromatic carbon ratio produced an oil rich in naphthenic structures.     

Determination of carbon C,CH, CH2 and CH3 group abundances in liquids derived from petroleum and coal using selected multiplet 13C n.m.r. spectroscopy

Selected, multiplet C n.m.r. spectra are obtained for three test samples deriving from petroleum and coal sources, by combining gated spin echo (GASPE) and conventional spin echo ¹³C n.m.r. procedures. Each selected multiplet spectrum contains resonances due to only one of the following groups: aromatic C or CH or aliphatic C, CH, CH₂orCH₃. In general artifacts contribute only minor intensity to individual spectra, with the separation between aliphatic CH and CH₃ spectra being the most difficult to achieve. Each spectrum can be integrated to yield the relative abundances of CH_n groups (n = 0 to 3). Selected multiplet ¹³C n.m.r. spectra provide a more detailed view of the component hydrocarbon groups in fossil-fuel derived materials than can be deduced from conventional ¹³C n.m.r. spectra.     

Relaxation spectrometry of polyethylene in urea-polyethylene complex by BL n.m.r. and e.s.r. measurements

The molecular motions of polyethylene in urea-polyethylene complexes have been studied by e.s.r. and BL n.m.r. The e.s.r. spectra of alkyl free radicals located along the polymer chains were recorded and the temperature dependences of hyperfine splitting widths due to the β-protons (ΔH_β1, ΔH_β2) and linewidths were estimated. A decrease in (ΔH_β1 ? ΔH_β2) and narrowing (which appears over a wide temperature region) was found. The motional narrowing of line widths in the _BL n.m.r. spectra were also found. Correlation times for the molecular motion of polyethylene molecules were calculated from this magnetic resonance data, taking into account the distribution of relaxation times according to Miyake's equation. It was concluded that the molecular motions studied by e.s.r. and n.m.r. were the same. Relaxation time spectra indicated higher activation energies (10 kcal) than those calculated for a system with a single correlation time.     

Distribution of aliphatic and aromatic carbons in H-Coal liquids by quantitative 13C FT-n.m.r. spectroscopy

Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, f_a, the C_ar:C_al ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.     

Relaxation of 13C and 15N nuclei by solvent-refined coal

The effects of changing various spectroscopic parameters on the solid-state and solution ¹³C-nuclear magnetic resonance (n.m.r.) spectra of solvent-refined coal have been investigated. Solution spectra were obtained with the use of broad band decoupling, inverse gated decoupling and coupling techniques. Conventional relaxation reagent (Cr(acac)₃) was sometimes added to the solvent-refined coal. The effects of pulse delay on the total signal intensity, and on the intensity of the signal from aromatic carbon have been measured. The results show that inverse gated decoupling with pulse delays of 10 s is needed for complete relaxation of solvent-refined coal, but pulse delays of 6 s can give accurate estimations of aromaticity. However, it is recommended that conventional relaxation reagent such as Cr(acac)₃ be added to ensure relaxation if shorter pulse delays are used. The effect of solvent-refined coal on relaxation of some pure compounds in solution has also been studied. Solvent-refined coal acts as a relaxation reagent on ¹³C nuclei in benzene, toluene and ethylbenzene. It can also relax ¹⁵N nuclei in aniline, N,N-dimethylaniline and nitromethane. Spin-lattice relaxation times (T₁'s) of selected nuclei have been measured and the contribution of solvent-refined coal to relaxation (T₁SRC) has been calculated. Solid-state 13C-n.m.r. spectra have been obtained using the cross-polarization (CP) technique with magic-angle sample spinning (MASS). A variety of cross-polarization times and recycle times have been used. The results show that no serious errors in measurement of aromaticity (f_a) are caused by using a contact time as short as 1 ms and a recycle time of 0.3 s. There is good agreement between f_a's obtained by solution and solid-state n.m.r., and as solid-state spectra can be obtained in only a fraction of the time needed to obtain a solution spectrum (≈$\text{1}\text{20th}$), CP-n.m.r. is the method of choice for analysis of f_a of solvent-refined coal. The results also show that CP-MASS n.m.r. can be used to estimate the fraction of aromatic carbon which is unprotonated in solvent-refined coal and, hence, indirectly, the fraction of hydrogen which is aromatic.     

34 GHz e.p.r. study of vanadyl complexes in various asphaltenes: Statistical correlative model of the coordinating ligands

High precision 34 GHz e.p.r. measurements were performed to study the coordination of vanadyl complexes in various asphaltenes. The spin-Hamiltonian parameter analysis indicates that the asphaltenes can be classified into those which have g- and A-parameters nearly identical to those for the vanadyl tetraphenyl porphyrins doped in carbonaceous materials and those for which these parameters are nearly identical to those for the vanadyl etioporphyrins. Quantitative statistical analysis of the parameters for model compounds with coordination N₄, N₂S₂, NS₃, S₄, S₂O₂, N₂O₂ and O₄ shows that these parameters cannot be used to predict the coordination for various asphaltenes. It is found that g₀ is a better parameter than A₀ to predict the coordination, although it cannot resolve the N₄, S₄ and S₂O₂ coordinations. However, the spin-Hamiltonian parameter resolution was sufficient to distinguish between those vanadyl complexes present in porphyrins, humates and minerals. The importance of high precision e.p.r. measurement at 34 GH_z or higher frequencies for model compounds and chromatographically-separated fractions is discussed.     

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.     

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.