Wide-line <Superscript>1</Superscript>H NMR study of mesomorphic states of 4′-(octyloxy)-4-biphenylcarbonitrile

A sample of 4′-(octyloxy)-4-cyanobiphenyl (8OCB) was studied in the temperature range −60–80°C by wide-line ¹H NMR. The line shapes, half-widths, and second moments were determined. For the smectic phase of 8OCB, the relaxation times T ₁ and T ₂, the correlation time τ_c, and the degree of order were estimated. The ¹H NMR spectral patterns and characteristics were found to be quite different for the crystalline, smectic, and nematic phases of 8OCB, which makes it possible to reliably identify the corresponding transitions and assess the molecular dynamics and molecular order of a structure. The temperature ranges, stability conditions, and other characteristics of the liquid crystalline phases that form on heating 8OCB were determined.     

Wide-Line 1H NMR and DSC study of phase states of mesomorphic states of 4′-n-alkoxy-4-biphenylcarbonitrile mesogens (n = 3 and 7)

4′-(Propyloxy)-4-cyanobiphenyl (3OCB) and 4′-(heptyloxy)-4-cyanobiphenyl (7OCB) have been studied in the temperature range 20–80°C by wide-line ¹H NMR and DSC. The ¹H NMR line shapes, half-widths, and second moments, as well as the relaxation characteristics of separate lines, are discussed. The DSC data are compared with the specific features of mesogenic transformations of these homologues and ¹H NMR data. At certain temperatures depending on the composition of alkyl moieties, a dynamically disordered fraction of molecules appear in solid crystals. These molecules are involved in the thermotropic transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal. The temperature ranges, stabilities, and other characteristics of the transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal were determined.     

Wide-line <Superscript>1</Superscript>H NMR study of 4′-(pentyloxy)-4-biphenylcarbonitrile in different phase states

A sample of 4′-(pentyloxy)-4-biphenylcarbonitrile was studied in the temperature range 20–70°C by wide-line ¹H NMR. The line shapes, half-widths, and second moments were determined. At 20°C, the spectrum is a broad structureless line, which was split into three components at temperatures above 47°C. This pattern persisted up to 65°C, with the components becoming narrower. Above 68°C, the spectrum rapidly collapses to give a structureless narrow line with a width δH < 0.01 G. Analysis of the spectra and comparison with theoretical calculations made it possible to elucidate the transition of the sample from the crystalline to the nematic and isotropic phases, as well as to determine the temperature range of the stability of the liquid-crystalline phase and the role of rotational mobility of protons of different functional groups and sometimes of these groups as a whole in the mechanisms of phase transitions.     

1H and 13C NMR Spectroscopy of Stereoisomeric 2′-deoxy-C-Nucleosides

Eleven furanosyl 2′-deoxy-C-nucleosides with β-D-erythro, α-D-erythro and β-D-threo configurations have Been studied by IH and ¹³C NMR spectroscopy recorded in CDC1₃ and/or DMSO-d ₆. Results obtained indicate that each of the three stereoisomeric configurations studied are identifiable by ¹H and ¹³C NMR spectroscopy using a combination of coupling constant and chemical shift criteria.     

Application of DSC–TG and NMR to study the soil organic matter

The environmental concern on soil exploitation, linked to global warming by the Kyoto protocol, is responsible for increasing interest in the understanding of the role of the composition and structure of the soil organic matter (SOM) on soil carbon, C, dynamics. Thermal analysis and nuclear magnetic resonance (NMR) are applied to study the thermal properties, the structure and composition of the SOM of six samples with different C contents in order to improve the interpretation of results given by thermal analysis. Results showed that the direct integral of the combustion peaks obtained by DSC and the percentage of SOM given by TG were both directly related to the quantity of total soil C. Thus, soils with higher C content showed higher energy content too. The combustion temperatures of the curves given by DSC are those reported for labile OM. NMR results indicated the presence of aliphatic C, carbohydrates, and a weak signal in the aromatic C band in all the samples that was not detected in the DSC curves. Only two samples showed carboxyl/carbonyl C which was not detected by DSC also.     

Synthesis and some transformations of 2-(2′-thienyl)benzothiazole

Condensation of ortho-aminothiophenol with 2-thenoyl chloride in 1-methyl-2-pyrrolidone was used to synthesize 2-(2′-thienyl)benzothiazole. Its reactions of electrophilic (nitration, bromination, oxymethylation, formylation, acylation) and radical (nitration, arylation) substitution were studied.     

Synthesis and mesomorphic properties of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives

Three series of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-x), which possessed 5-nitrobenzimidazole (nM-N series), benzimidazole (nM-H series) or 5-methylbenzimidazole (nM-M series) units at the end of the molecule, were synthesised and characterised by infrared, ¹H- and ¹³C-nuclear magnetic resonance spectra, electrospray ionisation-mass spectrometry and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. All the compounds exhibited enantiotropic smectic mesophases with wide temperature domains for a carbon number in the alkoxy chain from 6 to 16, where the mesophase ranges were 14–91°C and 17–99°C during heating and cooling processes for the nM-N compounds, 7–25°C and 8–49°C for the nM-H compounds and 48–81°C and 52–85°C for the nM-M compounds, respectively. The effect of the length of alkoxy chain on mesomorphic properties was discussed. The nM-N and nM-M exhibited a much wider mesophase range whether during heating or cooling process than the corresponding nM-H series, especially for the longer terminal chain (n > 8), which indicated that the substituent in the benzimidazole moiety was helpful in increasing the mesophase stability.     

N′-(α-acetoximinoalkyl)diazene-N-oxides and some of their transformations

Nitroso compounds of the aromatic and aliphatic series react with O-acetylalkanoylamidoximes in the presence of dibromoisocyanurate, forming the previously unknown N-(-acetoximinoalkyl)diazene-N-oxides, which under gaseous NH₃ or oxalic acid in methanol lose the acetyl group and as a result are transformed into the previously unknown N-(-hydroximinoalkyl)diazene-N-oxides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 109–114, January, 1991.     

Features of the synthesis of 1,1′-Phenylenebis(1H-tetrazoles) and their transformations in basic environment

Reactions of substituted 1,3- and 1,4-phenylenediamines with sodium azide and triethyl orthoformate in the presence of acetic acid led to the formation in high yields of the corresponding 1,12 -phenylenebis(1Htetrazoles). The presence of electron-acceptor groups in the molecules of the initial diamines reduces the yield of the target heterocycles. With 2-nitro-1,4-phenylenediamine the prevailing product was 2-nitro-4-(1H-tetrazol-1-yl)aniline. The obtained bistetrazoles in basic environment suffer an opening of one or both heterocycles forming cyanamides.     

2-Dimensional and computational analysis of the 1H NMR spectrum of the bis(2,2′-bipyridine)carbonatocobalt(III) ion†

The use of COSzY and NOESY ¹H NMR techniques allows for the assignment of ¹H NMR chemical shifts for the bis(2,2′-bipyridine)carbonatocobalt(III) ion. These assignments are further confirmed by DFT GIAO-NMR calculations using the model chemistry B3LYP/6-31G(d,p) and invoking the IEF-PCM representing acetone. These computations also allow for initial quantification of a cis influence on the chemical shift due to anisotropic ring currents and a much less pronounced trans influence on the chemical shift due to inductive effects. The computational model employed is also compared to previously accepted models for anisotropic effects.     

Complexation studies of pioglitazone hydrochloride and β-cyclodextrin: NMR (1H, ROESY) spectroscopic study in solution

Pioglitazone hydrochloride (PIO) is an agonist of the peroxisome proliferator-activated receptor γ (PPARγ), used to treat diabetes. ¹H-NMR spectroscopic analysis of varying ratios of β-cyclodextrin (β-CyD) and PIO in D₂O confirmed the formation of β-CyD–PIO inclusion complex in aqueous solution. The 1:1 stoichiometry of β-CyD–PIO inclusion complex was determined by Scott’s plot method and binding constant (K _a ) was calculated to be 155 M^?1. 2D ROESY experiments confirmed that the phenyl ring of PIO act as a guest and deeply penetrate in β-CyD cavity from wider as well as narrower rim side and form two 1:1 stable inclusion complexes. Some of the PIO protons exhibited splitting, in the presence of β-CyD, indicating chiral differentiation of PIO by β-CyD.     

(1)H and (13)C NMR studies of asymmetrically substituted bis- and tris-Tröger's bases

The (1)H and (13)C NMR spectra of two stereoisomeric bis-Tr?ger's bases and four stereoisomeric tris-Tr?ger's bases asymmetrically substituted on the external aromatic rings were recorded and the corresponding signals assigned. The relative configuration of the stereogenic units has been unequivocally determined on the basis of homoallylic couplings and NOE experiments.     

Dielectric,electro-optic and infrared and 1H NMR spectral properties of methyl- and t-butyl-substituted (η6-benzene)tricarbonylchromium(0) complexes: a study of solvent effects

Dipole moment, microwave dielectric absorption, electric birefringence and infrared and ¹H NMR spectral data are presented for [Cr(CO)₃(η⁶-C₆H₆)] and for some of its methyl- and t-butyl-substituted derivatives in the non-dipolar solvents, cyclohexane, benzene and dioxane. Atomic polarisations for these complexes are shown to be negligibly small. Specific interactions are shown to occur between dioxane or benzene solvent molecules and the coordinated arene which acts as an electrophile. The effects on such interactions of progressive methyl or t-butyl group insertion on the arene nucleus are studied. In 1,3,5-tri-t-butylbenzenetricarbonylchromium(0), “face-to-face” associations between the arene ligand and solvating benzene are sterically inhibited. Direct complexation with chromium is shown to be improbable with these solvents. The solute polarisability tensor of [Cr(CO)₃(η⁶-C₆H₆)], unlike the dipole moment vector, is not changed by interaction with dioxane. With methyl or t-butyl substitution, the solute polarisability anisotropy in dioxane tends to decrease, relative to that in cyclohexane. Electric birefringences and ¹H NMR chemical shifts are interpreted in terms of transient stereospecific solute-benzene associations additional to “face-to-face” charge-transfer interactions. Benzene-induced upfield shifts or aryl protons (ASIS) decrease in magnitude with progressive methyl or t-butyl substitution.     

Kinetics and mechanism of mercuration of N-(substituted benzylidene)-4-toluidines

In order to investigate the mechanism of mercuration reaction of substituted ben-zylideneanilines, kinetic measurements of these reactions at different temperatures (40-60℃) inmethanol-l,4-dioxane (1/1, V/V) were carried out and Hammett ρ value for C-phenyl substituentsof-0.61 for the N-(substituted benzylidene)-4-toluidine series was obtained. Thermodynamicparameters E_a, △S~≠ were obtained for the reaction of different. N-(substituted benzylidene)-4-toluidines. It was found that this ortho-mercuration was brought about by an internal cyclometal-lation process involving the imino-moiety.     

Synthesis and Crystal Structure of(p-{2-[p-(5′-Phenyl-1′,3′,4′-oxadiazole-2′-yl)-phenyl]-vinyl}-phenyl)-di-p-tolyl-amine

The crystal of the title compound (C36H29N3O,Mr = 519.62) has been prepared and structurally determined by X-ray single-crystal diffraction. It crystallizes in triclinic P ī space group with the crystal cell parameters: a = 12.544(4), b = 14.112(4), c = 17.770(5)A, α = 96.150(6), β = 106.112(5), γ = 107.156(5)°, V = 2825.7(14) ?3, Z = 4, Dc = 1.221g/cm3, μ(MoKα) = 0.074 mm-1 , F(000) = 1096,the final R = 0.0747 and wR = 0.1632 for 4713 observed reflections with I >2σ(I). The E-stereochemistry of the title compound can be confirmed by the result of the X-ray diffraction analysis.     

1H and 13C NMR characteristics of β-blockers

The β-blockers are important drugs and decades of clinical experience proved their high medical status. However, to the best of our knowledge, there is no complete assignment of (1)H and (13)C NMR resonances of popular representatives: acebutolol, alpenolol, pindolol, timolol and propranolol and the published NMR data on carvedilol and atenolol are incorrect. Therefore, (1)H and (13)C NMR spectroscopy was applied for the characterization of a series of β-adrenolytics: carvedilol (1), pindolol (2), alprenolol (3), acebutolol (4), atenolol (5), propranolol (6) and timolol (7). Two-dimensional NMR experiments (COSY, HMQC, HMBC, NOESY) allowed the unequivocal assignment of (1)H and (13)C spectra for solution (DMSO-d(6) ). Salts and bases can be easily distinguished based on (13)C chemical shifts which are within 65.0-65.5 ppm (OC2) and 46.9-47.0 (NC3) for hydrochlorides and larger, ca. 68.4 ppm (OC2) and 50.3-52.6 (NC3) for bases. NMR data of 1-7 should be included in pharmacopoeias.     

1H NMR and UV spectroscopic study of inclusion complex formation between pyridoxine and β- and γ-cyclodextrins

Inclusion complex formation between pyridoxine and - and -cyclodextrins in aqueous solution has been investigated by¹H NMR and UV spectroscopy. Both complexes exhibited a 1:1 stoichiometry and the inclusion process has been shown to perturb the equilibrium between the lactim and the lactam tautomer of pyridoxine, with a preferential inclusion of the former, less polar tautomer.     

Carbonium ion stabilization by (η5-cyclopentadienyl)dicarbonylnitrosylchromium; a 1H and 13C NMR study

the ¹H and ¹³C NMR spectra of a series of (η⁵-cyclopentadienyl)dicarbonylnitrosylchromium-substituted carbonium ions have been determined. These data suggest that the same mechanism is responsible for the stabilization of carbonium ions by (η⁵-cyclopentadienyl)dicarbonylnitrosylchromium as is operational in the analogous ferrocene and cymantrene complexes.