Effect of confinement on ionic liquids dynamics in monolithic silica ionogels: 1H NMR study

(1)H MAS NMR and temperature-dependent relaxation time measurements were carried out for the first time on ionic liquids confined in monolithic silica matrices and enabled us to show that the ionic liquids' dynamics experienced only a very small slowing-down. The confinement preserved the ionic liquids' properties and, moreover, allowed liquid-like behaviour at temperatures below the crystallisation temperature of genuine ionic liquids. This study highlights the interest of the ionogel approach to all-solid state devices with genuine IL properties.     

1H and13C NMR spectra and structure of 2,3,4-trisubstituted sulfolanes

Conclusions The¹H and¹³C NMR spectra were studied for 2,3,4-trisubstituted sulfolanes and the isomerism of these compounds was determined, The use of chemical shift information is more convenient to determine the isomerism of polysubstituted cyclic compounds by PMR spectroscopy, while use of the direct carbon-proton coupling constants is more convenient for this problem when employing¹³C NMR spectroscopy.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2498–2501, November 1984.     

Decomposition of a NMR signal comprising a single resonance in exchange with a Pake doublet: Application to the analysis of H NMR spectra of water molecules embedded in synthetic clays

Conventional ¹H NMR spectra of water in clays generally consist of several broad overlapping resonances. However, when a type of water is partially oriented, it leads to a Pake doublet superposed to the resonances corresponding to different types of non-oriented water. With the help of a recent method based on nutation experiments, the proportions of the different kinds of water could be determined. Thus, we are able to determine interesting NMR parameters like dipolar couplings, exchange rate, and line broadening. These determinations are complemented by spin relaxation times and self-diffusion measurements which bring additional information about the dynamical behavior of water.     

1H NMR spectra of substituted phenazines

The ¹H NMR Spectra of 28 substituted phenazines have been measured and analysed with computer assistance. Substituent increments of chemical shifts were calculated for methoxy, carbomethoxy and methyl derivatives. The influence of these substituents on coupling constants has been examined.     

1H NMR spectra of monosubstituted phenanthrenes

The effects of various substituents on the chemical shifts and coupling constants of the ¹H NMR signals of phenanthrene are reported and discussed in terms of structural features.     

1H NMR spectra and electronic structure of 3-arylmethyl-idenephthalide and 3-arylthiomethylidenephthalide derivatives

The ¹H NMR spectra of trans-3-phenylmethylidenephthalide and trans-3-phenylthiomethylidenephthalide derivatives were investigated. After applying a correction for the anisotropy of substituents and/or for changes of ring current in the substituted aromatic ring, linear correlations were obtained between the chemical shifts of protons of the substituted phenyl group and the methine group and s? constants of substituents. The influence of the bridge heteroatom on the transfer of electronic effects of substituents through the molecules under study is discussed.     

1H, 2H and 13C NMR spectra and molecular dynamics of some solid alkylene-aromatic polyesters

Molecular dynamics of some mesomorphic main–chain alkylene–aromatic polyesters have been investigated by means of NMR spectra of various nuclei over a wide temperature range. In solid polymers regions of different molecular mobilities coexist and their fractions are determined by the sample temperature and thermal history. The sample annealing leads to the growth of rigid fraction. It was found that below the glass transition temperature the only forms of large–scale mobility are the torsional vibrations and flips of para–phenylene groups, while spacer groups are virtually rigid. Above the glass temperature almost all phenylene rings undergo flipping motions and methylene groups of the spacer take part in complicated motions of both anisotropic and isotropic character.     

Electronic structure, 1H NMR spectra,and reactivity in certain tricyclic heteroaromatic systems

The simple MO LCAO method was used for calculations on 4H-imidazo[5,1-b]benzimidazole, imidazo[5,1-b]benzoxazole, imidazo[5,1-b]benzothiazole, and a number of their derivatives. Inclusion of the unshared pairs of the hetero atoms at positions 4 and 9 in the -electron system has a considerable effect on the stability of compounds of this type. The ¹H NMR spectra were recorded for 4-methyl-imidazo[5,1-b]benzimidazole and imidazo[5,1-b]benzoxazole derivatives, and a similarity was found between the chemical shifts of the imidazole ring protons and the -electron densities at the adjacent carbon atoms. Calculation of a series of models for the cations and measurements of the basicity constants show protonation of 4-methylimidazo[5,1-b]benzimidazole takes place at the nitrogen atom in position 2. The calculated values for the electronic structure and reactivity indices in the investigated series of tricyclic systems were compared with their chemical properties.     

Towards the automatic analysis of NMR spectra: part 6. Confirmation of chemical structure employing both 1H and 13C NMR spectra

A method of comparing predicted and experimental chemical shifts was used to confirm or refute postulated structures. 1H NMR spectra returned all true positives with a false positive rate of 4%. When an analogous procedure was adopted for 13C NMR spectra, the false positive rate dropped to 1%, whereas the more practical HSQC data yielded a false positive rate of 2%. If the HSQC results were combined with 1H results, a false positive rate of 1% resulted, 4 times more accurate than 1H alone.     

Spec2D: a structure elucidation system based on 1H NMR and H-H COSY spectra in organic chemistry

A system for structure elucidation based on proton NMR spectra has been developed. The system, named Spec2D (system for spectra from 2D-NMR), incorporates 1H NMR and H-H correlation spectroscopy (COSY) spectral information obtained from 2D-NMR experiments. 2D-NMR is important for the structure elucidation because it provides information about the relationships among differently situated protons in the structures of unknown compounds. The system uses the concepts of molecular graphs. The improved representation of substructures as well as several novel algorithms for structure generation have been devised to solve the combinatorial problem and to reduce the processing time. Spec2D consists of a knowledge base, an analysis module, and a candidate structure generator module. Spec2D proposes candidate structures from only 1H NMR and H-H COSY spectral information of an unknown compound without any 13C NMR spectral or structural information, such as molecular formulas. Spec2D has the capability to propose the "new" structure of an unknown compound, if the corresponding substructures are included in the knowledge base.     

1H and 13C NMR spectra of Strychnos alkaloids: Selected NMR updates

The PBE0/pcSseg-2//pcseg-2 calculations of ¹H and ¹³C NMR chemical shifts were performed for a classical series of 12 Strychnos alkaloids (except for the earlier studied parent strychnine), namely akuammicine, isostrychnine, rosibiline, tsilanine, spermostrychnine, diaboline, cyclostrychnine, henningsamide, strychnosilidine, strychnobrasiline, holstiine, and icajine. It was found that the calculated ¹H and ¹³C NMR chemical shifts show markedly good correlations with available experimental data, as characterized by a mean absolute error of 0.22 ppm for the range of 8 ppm for protons and 1.97 ppm for the range of 180 ppm for carbons. Complementarily, the present results provide essential NMR update and fill a gap in the NMR data of this distinguished group of vitally important natural products.     

Slow dynamics in a liquid crystal: 1H and 19F NMR relaxometry

Spin-lattice relaxation rates (R(1H) and R(1F)) of two nuclear species ((1)H and (19)F) are measured at different temperatures in the isotropic phase of a liquid crystal (4(')-butoxy-3(')-fluoro-4-isothiocyanatotolane-4OFTOL), over a wide range of Larmor frequency (10 kHz-50 MHz). Their dispersion profiles are found to be qualitatively very different, and the R(1F) in particular shows significant dispersion (varying over two orders of magnitude) in the entire isotropic range, unlike R(1H). The proton spin-lattice relaxation, as has been established, is mediated by time modulation of magnetic dipolar interactions with other protons (case of like spins), and the discernable dispersion in the mid-frequency range, observed as the isotropic to nematic transition is approached on cooling, is indicative of the critical slowing of the time fluctuations of the nematic order. Significant dispersion seen in the R(1F) extending to very low frequencies suggests a distinctly different relaxation path which is exclusively sensitive to the ultra slow modes apparently present in the system. We find that under the conditions of our experiment at low Zeeman fields, spin-rotation coupling of the fluorine with the molecular angular momentum is the dominant mechanism, and the observed dispersion is thus attributed to the presence of slow torques experienced by the molecules, arising clearly from collective modes. Following the arguments advanced to explain similar slow processes inferred from earlier detailed ESR measurements in liquid crystals, we propose that slowly relaxing local structures representing such dynamic processes could be the likely underlying mechanism providing the necessary slow molecular angular momentum correlations to manifest as the observed low frequency dispersion. We also find that the effects of the onset of cross-relaxation between the two nuclear species when their resonance lines start overlapping at very low Larmor frequencies (below ~400 kHz), provide an additional relaxation contribution.     

19F and 1H NMR spectra of halocarbons

19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed.     

1H and 13C NMR spectra of N-vinylpyrroles

The position of the substituants in 2, 3-dialkyl-1-vinylpyrroles and 7-methyl-1 vinyl-4,5,6,7-tetrahydroindole was established on the basis of the ¹H and ¹³C NMR spectra. It was found that the S-trans conformation of the N-vinyl group is preferred. It is shown that the condensation of ketoximes with acetylene proceeds through the formation of free pyrroles and that vinyl oximes are not intermediates in the condensation.     

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

The ¹H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO‐CDCl₃) are large (1–2 ppm) for the NH protons but smaller and negative (?0.1 to ?0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The ¹H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl₃. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl₃. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.     

1 H and 13 C NMR spectra and structure of 2-trichloromethyl-4-methylene-1,3-dioxolanes

The ¹H and ¹³C NMR spectra of a number of 5-substituted 2-trichloromethyl-4-methylene-1,3-dioxolanes were studied. It was observed that the exocyclic double bond is in effective conjugation with the 3–0 ring atom. The configuration of the substituents was established, and a conformational model of these heterocycles of the envelope type with the 1–0 atom deviating from the plane in which the remaining ring atoms are situated is proposed. The applicability of the ¹³C NMR spectra for the determination of the configuration of the compounds is demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1176–1180, September, 1976.