Functionalization at the double-bond region of jojoba oil. 9. solid-state nuclear magnetic resonance characterization of substituted jojoba wax chemically bonded to a polystyrene matrix

Solid extractants for metal ions have been prepared by chemical bonding of jojoba wax to a polystyrene backbone, followed by phosphonation or sulfur-chlorination of the jojoba moiety. In this study, the intermediates and final solid products of the reactions were characterized by solid-state ¹³C and ³¹P nuclear magnetic resonance spectroscopy. The spectra showed the expected chemical shifts of the atoms involved in the chemical reactions, as well as other parts of the reacting molecules. Thus, the carbonyl carbon of the jojoba chain appears at 175 ppm, the methyl carbons at 15 ppm, the polystyrene backbone at 40–42 ppm (aliphatic carbons) and 128, 137, 143–147 (aromatic carbons). Carbons adjacent to N, S, and P appear at 45–55, 60, and 48 ppm, respectively.     

13C n.m.r. determination of units formed by irregular addition in polyisoprene

¹³C n.m.r. spectroscopic data obtained for model compounds imitating regular and irregular addition of monomer units in linear polyisoprene are compared with the chemical shifts calculated using the empirical regularities found for the branched alkanes and alkenes and a good correlation is established. The validity of the results obtained was confirmed by investigation of the carbon spectra of hydrogenated and unhydrogenated polyisoprenes which contain chain fragments with irregular addition of units. Samples of hydrogenated polyisoprene are shown to give resonance lines that correspond to the methylene carbons of head-to-head and tail-to-tail addition and show chemical shifts at 34.62 ppm and 27.61 ppm, respectively. For the unhydrogenated polyisoprenes, the methylene carbons of trans- and cis-units in head-to-head addition were found to absorb at 38.6 ppm and 31.4 ppm, respectively, with those in the tail-to-tail addition of both isomers absorbing at 28.4–28.8 ppm. The latter findings offer a practical means of characterizing irregularities in polyisoprenes.     

Characterization of whole coals by 13C CP/MAS spectroscopy at high field

Solid-state 50-MHz ¹³C spectra essentially free of spinning sidebands have been constructed for three bituminous coals by the addition of echo spectra having phase-altered spinning sidebands (PASS). The echo spectra are produced by a modified version of the Dixon pulse sequence. Quantitative analysis of the aromatic carbon content (f_a) from PASS spectra for the three coals compares favourably with results obtained by other methods. Values of f_a are found in the range 0.69–0.73. Removal of the unwanted spinning bands allows absorptions for specific structural units present in the coals to be distinguished and assigned. Spectra show an upfield shoulder at 13–15 ppm, and moderately intense absorptions at 20–24 ppm and ≈30 ppm which are characteristic of several aliphatic structures in different steric environments. In addition to the main aromatic band at ≈120 ppm, absorptions for substituted aromatic carbons appear at ≈140 and ≈155 ppm. Less intense signals from several carbonyl functional groups (160–190 ppm) and oxygen- and nitrogen-substituted aliphatic groups (50–90 ppm) are also present.     

Substituent Effects on 13C Chemical Shifts of Aromatic Carbons in β-O-4 and β-5 type Lignin Model Compounds

Abstract

Substituent effects on the chemical shifts of aromatic carbons in lignin model compounds have been elucidated from ¹³C NMR spectra of guaiacyl and syringyl type monomerio and β-O-4 model compounds and guaiacyl type β-5 model compounds. Evaluation of the observed values of substituent chemical shift (SCS) for the aromatic carbons leads to elucidation of a generalized SCS additivity rule, for estimation of the chemical shifts of aromatic carbons in ring A of β-O-4 and β-5 type substructures in model compounds and in ring B of β-O-4 substructures in lignin preparations, with errors of less than 1 ppm. The rule is applicable to substructures of both guaiacyl and syringyl types, using an appropriate parent compound as reference instead of benzene. Signals in the aromatic region of the ¹³C NMR spectra of β-O-4 and β-5 type model compounds are reassigned on the basis of the observed SCS's as well as APT spectra of the compounds.     

Assignment of all Diastereomers of Perhydrofluorene in a mixture using 13C NMR spectroscopy

By hydrogenation of fluorene 1 using different catalysts, mixtures containing variable amounts of the six possible diastereomers of perhydrofluorene 2 were obtained. The ¹³C NMR spectra of all diastereomers have been determined in these mixtures whithout previous separation procedures. By molecular mechanics calculations the structures of the preferred conformations were simulated for all diastereomers. The substituent induced ¹³C NMR chemical shifts in conformers were calculated by using increments for the non-bonding 1,3-synaxial interactions. Three stereochemical increments, combined with the shift values found earlier by Beierbeck and Saunders, were sufficient to calculate the chemical shift differences of conformers empirically. The assignment of relative configurations of the diastereomers was possible by comparison of the empirically calculated and experimental ¹³C chemical shifts of the clearly distinguishable bridgehead carbons. The difference between calculated and experimentally determined shift values was only 1.3 ppm, averaged over all bridgehead carbons.     

Two-dimensional solid-state NMR studies of crystalline poly(ethylene oxide): Conformations and chemical shifts

The torsion angles of the OC-CO bonds in crystalline poly(ethylene oxide), PEO, were investigated by solid-state nuclear magnetic resonance (NMR). Two-dimensional double-quantum (DOQSY) spectra indicate that the OC-CO bonds are all gauche with an average torsion angle of ψ=74±4° and a narrow torsion-angle distribution, σ_ψ<8°. This is contradictory to the wider range of gauche torsion angles in the distorted helical structure previously proposed based on X-ray fiber diffraction. The low-temperature magic-angle-spinning (MAS) ¹³C NMR spectrum of unlabeled PEO contains four maxima and several shoulders, over a range of 3.1 ppm. Deconvolution of this spectrum, together with two-dimensional ¹³C INADEQUATE NMR and exchange MAS spectra, suggests a possible assignment of chemical shifts to the 14 carbons in the 7₂ helical repeat unit. The small line widths of the individual peaks indicate that the helical repeat unit is accurately replicated throughout the crystals. The results show that packing effects or small conformational differences can change chemical shifts by amounts that had previously been ascribed only to trans/gauche differences.     

The immobilization of iron(III) aminopyridine complex on MCM-41: its preparation and characterization

2-Aminopyridinyl iron(III) complex was grafted on chlorosilane modified mesoporous MCM-41 to give MCM-Py-Fe(III). The immobilization was confirmed by FT-IR, ¹³C, ²⁹Si, ¹⁵N CP/MAS NMR, nitrogen adsorption–desorption study and elemental analysis. The powder XRD and TEM microscopy studies of the hybrid material confirmed the retention of the well-ordered honeycomb hexagonal structure in MCM-Py-Fe(III). The specific surface area of MCM-Py-Fe(III) was found to be 455 m² g^?1 and it had a pore volume of 0.27 cm³ g^?1 with an average pore diameter of 26.7 Å. The ¹³C CP/MAS NMR of MCM-Py-Fe(III) showed chemical shifts in the range of 113–155 ppm, which was assigned to the aromatic carbons in the pyridine ring. The ¹⁵N CP/MAS NMR showed the presence of chemical shifts at 550, 426 and 401 ppm for the three nitrogen atoms in the catalyst.     

The calculation of sensitometric properties of 1,2,4-triazolo[1,5-a]pyrimidines

Quantitative structure–property relationships were proposed by using artificial neural networks and information received from ¹³C NMR spectra. The suitability of 1,2,4-triazolo[1,5-a]pyrimidines as stabilizers in photographic silver halide materials was determined from their chemical structures. For the numeric coding of the chemical structures of differently substituted 1,2,4-triazolo[1,5-a]pyrimidines 1 – 44 only information available from their ¹³C NMR spectra was used. Even an assignment of the ¹³C NMR chemical shift values to the carbons was not necessary. The best results were achieved by combination of the ¹³C NMR chemical shifts of carbons of the basic heterocycle and the relative fog D_rel using a feed-forward two-layer neural network. For some compounds with a good stabilizing effect the calculated results strongly differ from experimental values giving indication of a mechanism which is not covered by the ¹³C NMR chemical shifts.     

Effects of Solvation and Ionization on 13C NMR Spectra of Lignin Model Compounds,Spruce Milled Wood Lignin and Kraft Lignin

The effects of alkali and polar aprotic solvent on the aromatic carbons signals in ¹³C NMR (Carbon-13 nuclear magnetic resonance) spectra of lignin model compounds and spruce milled wood lignin (MWL) were studied. It was found that in 1 M aqueous NaOH signal shifts of C-1 and C-4 carbon atoms in the aromatic ring were the most noticeable in lignin models with free phenolic hydroxyl groups, which are ionized under the conditions. A similar effect in the spectra of the studied model compounds was observed in 0.5 M aqueous NaOD-deuterated dimethyl sulfoxide (DMSO) mixture (DMSO: water ratio 3:7 v/v). The model data help explaining changes in the ¹³C NMR spectra of MWL and lignin in situ dissolved in spruce kraft black liquor caused by ionization. In the ¹³C NMR spectra of spruce black liquor the signals of phenolic and non-phenolic lignin units are clearly separated and do not overlap with the signals of the carbon atoms of carbohydrates and other aliphatic products of wood degradation. The data obtained are useful in understanding the important role of solvation and ionization processes leading to lignin solubilization.     

Quantitative analysis and characterization of the products of the model reaction of n-butyllithium with excess 1,1-diphenylethylene: 1,1-Diphenylhexane and 1,1,3,3-tetraphenyloctane

The model reaction of n-butyllithium with excess (11 M equivalents) 1,1-diphenylethylene (DPE) was reinvestigated using modern characterization techniques including SEC, one dimensional and two dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy and electrospray ionization mass spectrometry (ESI MS). The products were the monoadduct, 1,1-diphenylhexane (nBuDPEH), and the diadduct, 1,1,3,3-tetraphenyloctane [nBu(DPE)₂H], formed in 62 mol% and 38 mol% yields, respectively, as determined by SEC and ¹H NMR spectroscopy. The ¹H NMR spectrum of 1,1,3,3-tetraphenyloctane exhibited a terminal methine triplet resonance at δ 3.71 ppm that was uniquely coupled to the adjacent methylene doublet resonance at δ 3.09 ppm, located between the two carbons, each bonded to two phenyl groups [–C(C₆H₅)₂-CH₂-CH(C₆H₅)₂. All of the characteristic ¹H and ¹³C NMR resonances for both adducts were assigned using 2D NMR spectroscopic methods. The diadduct, nBu(DPE)₂H, exhibited unique ¹³C NMR resonances at δ 50.79 ppm for the quaternary carbon resonance [CH₂-C(C₆H₅)_2?CH₂], and at δ 43.74 ppm for the methylene group isolated between the two carbons, each bonded to two phenyl groups [–C(C₆H₅)₂-CH₂-CH(C₆H₅)₂].     

Zur Zuordnung der 13C-chemischen Verschiebung substituierter Naphthaline aus Ladungsdichten mit Hilfe neuronaler Netze

The Assignment of the ¹³C-NMR Chemical Shifts of Substituted Naphthalenes from Charge Density with an Artificial Neural Network Neuronal networks are a new possibility to work with blurred data and informations. In this article, the use of a multilayer network with backpropagation of errors for the prediction of the ¹³C-chemical shifts of a series of substituted naphthalenes from the σ- and π- charge density of the corresponding carbon atoms (calculated by means of the PIMM program) will be described. The average uncertainty for the estimation of the ¹³C-chemical shifts of monosubstituted naphthalenes is only 2.1 ppm, for naphthalenes with more than one substituent about 4 ppm.     

13C-NMR analysis of formaldehyde resins

¹³C-NMR spectroscopy has been applied to the analysis of formaldehyde containing resins. Samples have been prepared from phenols, urea and melamine with formaldehyde. The chemical shifts of the carbon atoms in the resins were measured relative to TMS. All the samples could be dissolved in DMSO-d₆ which facilitated the comparison of signals in different resins. The spectra were interpreted with the aid of spectra of reference compounds and simple calculations based on additivity increments. Each type of resin gives a specific ¹³C-NMR spectrum in which lines can be assigned that give information on the structure of the resin in relation to the type of condensation or catalyst used. Moreover, the different ways in which formaldehyde is incorporated in the resins as methylene carbon can be unambiguously determined from the region between 20 and 100 ppm. This work shows that ¹³C-NMR spectroscopy is a powerful tool for the analysis of formaldehyde containing resins.     

NMR characterization of dihydrosterculic acid and its methyl ester

Cyclopropane FA occur in nature in the phosphoplipids of bacterial membranes, in oils containing cyclopropene FA, and in Litchi sinensis oil. Dihydrosterculic acid (2-octyl cyclopropaneoctanoic acid) and its methyl ester were selected for ¹H and ¹³C NMR analysis as compounds representative of cyclopropane FA. The 500 MHz ¹H NMR spectra acquired with CDCl₃ as solvent show two individual peaks at −0.30 and 0.60 ppm for the methylene protons of the cyclopropane ring. Assignments were made with the aid of 2D correlations. In accordance with previous literature, the upfield signal is assigned to the cis proton and the downfield signal to the trans proton. This signal of the trans proton is resolved from the peak of the two methine protons of the cyclopropane ring, which is located at 0.68 ppm. The four protons attached to the two methylene carbons α to the cyclopropane ring also show a split signal. Two of these protons, one from each methylene moiety, display a distinct shift at 1.17 ppm, and the signal of the other two protons is observed at 1.40 ppm, within the broad methylene peak. The characteristic peaks in the ¹³C spectra are also assigned.     

Solid-State 13C CP/MAS NMR for Alkyl-O-Aryl Bond Determination in Lignin Preparations

Several lignin preparations (Freudenberg lignin, Björkman lignin, and Pepper lignin), technical lignins (soda, soda-AQ, Kraft, Kraft-AQ, and hydrolysis), dimeric lignin model compounds, and different polysaccharides (galactoglucomannan, arabinogalactan, xylan, and arabinan) were analyzed by means of solid-state ¹³C CP/MAS NMR. Signals assignment in solid-state NMR lignin spectra was performed on the basis of the conducted studies and earlier published data. It was established that there exists strong linear correlation (r = 0.985) between Alkyl-O-Aryl inter-unit bond content in lignin and integral signals intensity in NMR spectra in the range of chemical shifts of 96–68 ppm. The integral signals intensity was measured in correlation with the reference integral signals in the range of chemical shifts of 162–102 ppm, typical for aromatic carbon atoms. To eliminate the effect, caused by carbohydrates contained in lignin, the correction factor of 0.67% of the area of integration per 1% of carbohydrates was determined. It was shown that the solid-state ¹³C CP/MAS NMR method allowed to determine Alkyl-O-Aryl bond content in both soluble and insoluble lignin preparations, and also to determine methoxyl groups content in soluble preparations.     

Effect of activation temperature on the surface copper particles and catalytic properties of Cu–Ni–Mg–Al oxides from hydrotalcite-like precursors

The Cu–Ni–Mg–Al oxides catalysts for furfural hydrogenation were prepared from the hydrotalcite-like precursors, and the effect of activation temperature on the Cu⁰ particles and catalytic properties of the catalyst was thoroughly investigated. The catalyst activated by H₂ at 300 °C was found to exhibit the best catalytic activity, due to the presence of the smallest Cu⁰ particles with a high dispersion. Moreover, the bigger Cu⁰ particles were active for furfuralcohol hydrogenolysis to 2-methylfuran in the liquid-phase (ethanolic solution), and the hydrogenation of the furan ring of furfuralcohol and 2-methylfuran on Cu⁰ particles was easily achieved in the vapour-phase.     

C NMR study of C-enriched single-wall carbon nanotubes synthesized by catalytic decomposition of methane

¹³C NMR spectra and spin-lattice relaxation times were measured for single-wall carbon nanotubes with 99.9 and 50.0% ¹³C enrichments and natural abundance (1.1% ¹³C) prepared by catalytic decomposition of CH₄. The ¹³C isotropic shift is about 116 ppm from tetramethylsilane, being estimated from magic-angle-spinning (MAS) spectra. The value does not depend on the degree of the ¹³C enrichment. The ¹³C MAS NMR spectra show two additional small peaks at 171 and 152 ppm, which are ascribed to carbon species at defects or edges. The line widths of the main isotropic peak in MAS spectra are about 30 ppm, the origin of which is mostly chemical shift dispersion, reflecting a distribution of diameter and helicity. The line width in the ¹³C static spectra originates from chemical shift dispersion, chemical shift anisotropy and dipole–dipole interactions between ¹³C spins as well as between ¹³C and ¹H spins at defects or edges. ¹H NMR spectra confirm the presence of H-containing species. The ¹³C spin-lattice relaxation is dominated presumably by interaction with magnetic impurities.     

New insights on electrochemical hydrogen storage in nanoporous carbons by in situ Raman spectroscopy

In situ Raman spectroscopy was exploited to analyze the interaction between carbon and hydrogen during electrochemical hydrogen storage at cathodic conditions. Two different activated carbons were used and characterized by different electrochemical techniques in two electrolytes (6 M KOH and 0.5 M Na₂SO₄). The in situ Raman spectra collected showed that, in addition to the D and G bands associated to the graphitic carbons, two bands appear simultaneously at about 1110 and 1500 cm⁻¹ under cathodic conditions, and then they disappear when the potential increases to more positive values. This indicates that carbon–hydrogen bonds are formed reversibly in both electrolytes during cathodic conditions. Comparing the two activated carbons, it was confirmed that, in both electrolytes, the hydrogenation of carbon atoms is produced more easily for the sample with lower amount of surface oxygen groups. In KOH medium, for the two samples, the formation of carbon–hydrogen bonds proceeds at more positive potential with respect to the thermodynamic potential value for hydrogen evolution. Furthermore, changes in the shape of the D band (due to an intensity increase of the D1 band) during the formation of carbon–hydrogen bonds suggest that hydrogenation of the carbon atoms increases the number of edge planes.     

Relative reactivities of amylose hydroxyl groups in the reaction with diketene

¹³C nuclear magnetic resonance (n.m.r.) spectra at 75.4 MHz of partially modified amylose with β-keto ester groups (degree of substitution (DS) ranging from 0.52 to 2.42) were studied in order to evaluate the selectivity of the reaction of amylose with diketene in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of individual hydroxyl groups decreases in the order C-6>C-3>C-2 for DS values up to ∼1.8. For higher DS values a negative deviation is observed for the hydroxyl group at C-6 and a positive deviation for the hydroxyl groups at C-2 and C-3. The DS values determined by ¹³C n.m.r. spectra are in good agreement with those found by chemical analysis.     

Oxidative Kupplung CH-acider Verbindungen mit p-Phenylendiaminen. VI. 13C-NMR-Untersuchung der Tautomerie und des Substituenteneffektes 4-substituierter Pyrazolin-5-one

Oxidative Coupling of CH-acid Compounds with p-Phenylendiamines. VI. ¹³C-N.M.R. Study of Pyrazolin-5-on Tautomerism and the Effect of 4-Substituents The ¹³C-n.m.r. spectra of a series of 4-substituted 3-methyl-1-phenyl-pyrazolin-5-ones 1–26 have been recorded and assigned. Examination of the chemical shifts of the heterocyclic ring carbons C-3, C-4, C-5 and the 1-phenyl carbons C_ipso and C_ortho permits to determine the preferred tautomeric forms of the compounds. In polar solvents like DMSO the OH-form is dominant, sometimes besides a small component of the CH-form. In nonpolar solvents like CDCl₃ the CH-form is preferred at room temperature besides a small component of the NH-form. Cooling or addition of CH₃OH to the solution shifts the tautomeric equilibrium to a higher amount of the NH-form. The influence of 4-substituents on the C-3, C-4 and C-5 chemical shifts have been compared with the effect of these substituents on the C_ipso and C_ortho carbons in benzene. A linear dependence between C-4 and C_ipso shows, that the effect of substituents in pyrazolin-5-ones and benzene is controlled by their electronegativity. The substituent effects are influenced remarkably by intermolecular hydrogen bondings to polar solvents and by intramolecular hydrogen bondings, if possible.     

The free-radically prepared copolymers of acrylonitrile with furfuryl alcohol and similar furan derivatives

The preparation of copolymers of acrylonitrile with furfuryl alcohol, furfuryl acetate, bis-2,5-hydroxymethyl furan and bis-2,5-acetoxymethyl furan by a free radical reaction is described. Proton and ¹³C-n.m.r. spectroscopy has been used to characterise the residues that form from the furan monomers by the addition reaction. The residues produced by a 5,4-addition to the furfuryl alcohol ring or by 2,3-addition to the 2,5-dihydroxyfuran ring are susceptible to acid and undergo a rearrangement which removes the olefinic structure. The copolymers are decomposed to a hard, glassy carbonaceous material by heating in nitrogen in a process that has been examined by thermogravimetric analysis and elemental analysis. The copolymers prepared from furan monomers that contain a methylol group decompose more readily at a lower temperature than those which lack the group or than those in which the alcohol has been acetylated.