Natural abundance 17O NMR study of 2- and 4-substituted benzoyl chlorides

Natural abundance ¹⁷O NMR chemical shift data for 17 ortho and para benzoyl chlorides recorded in acetonitrile at 75°C are reported. ¹⁷O NMR data for the para substituted benzoyl chlorides are correlated with ¹⁷O NMR data for similarly substituted acetophenones and methyl benzoates. The ¹⁷O NMR signals for ortho isomers are downfield (ca 30 ppm) from their para isomers; the downfield shifts are consistent with torsion angle change. The ¹⁷O NMR data for the para isomers gave good correlations with σ⁺ constants and with dual substituent parameters (DSP).     

NMR stereospecific long-range coupling and preferred conformations in some (E)- and (Z)-α-phenyl-β-[2-(N-methyl)nitropyrrolyl] acrylic acids

NMR data have been used to assign the stereochemistry to some new (E)- and (Z)-α-phenyl-β-[2-(N-methyl)nitropyrrolyl]acrylic acids. The (E)-molecules are biased in the s-cis conformation showing NMR spectroscopic features strictly depending on the conformation.The analysis of the NMR spectra reveals that the (Z)-isomers exist also in the s-cis conformation.     

The structure of phosphate and borosilicate glasses and their structural evolution at high temperatures as studied with solid state NMR spectroscopy: Phase separation,crystallisation and dynamic species exchange

In this contribution we present an in-depth study of the network structure of different phosphate based and borosilicate glasses and its evolution at high temperatures. Employing a range of advanced solid state NMR methodologies, complemented by the results of XPS, the structural motifs on short and intermediate length scales are identified. For the phosphate based glasses, at temperatures above the glass transition temperature T_g, structural relaxation processes and the devitrification of the glasses were monitored in situ employing MAS NMR spectroscopy and X-ray diffraction. Dynamic species exchange involving rapid P–O–P and P–O–Al bond breaking and reforming was observed employing in situ ²⁷Al and ³¹P MAS NMR spectroscopy and could be linked to viscous flow. For the borosilicate glasses, an atomic scale investigation of the phase separation processes was possible in a combined effort of ex situ NMR studies on glass samples with different thermal histories and in situ NMR studies using high temperature MAS NMR spectroscopy including ¹¹B MAS, ²⁹Si MAS and in situ ²⁹Si{¹¹B} REAPDOR NMR spectroscopy.     

Study on Nuclear Magnetic Resonance Logging T2 Spectrum Shape Correction of Sandstone Reservoirs in Oil-Based Mud Wells

The oil-based mud filtrate will invade the formation under the overbalanced pressure during drilling operations. As a result, alterations will occur to the nuclear magnetic resonance (NMR) response characteristics of the original formation, causing the relaxation time of the NMR T₂ spectrum of the free fluid part to move towards a slower relaxation time. Consequently, the subsequent interpretation and petrophysical evaluation will be heavily impacted. Therefore, the actual measured T₂ spectrum needs to be corrected for invasion. For this reason, considering the low-porosity and low-permeability of sandstone gas formations in the East China Sea as the research object, a new method to correct the incorrect shape of the NMR logging T₂ spectrum was proposed in three main steps. First, the differences in the morphology of the NMR logging T₂ spectrum between oil-based mud wells and water-based mud wells in adjacent wells were analyzed based on the NMR relaxation mechanism. Second, rocks were divided into four categories according to the pore structure, and the NMR logging T₂ spectrum was extracted using the multidimensional matrix method to establish the T₂ spectrum of water-based mud wells and oil-based mud wells. Finally, the correctness of the method was verified by two T₂ spectrum correction examples of oil-based mud wells in the study area. The results show that the corrected NMR T₂ spectrum eliminates the influence of oil-based mud filtrate and improves the accuracy of NMR logging for calculating permeability.     

Synthesis and spectral characterization of some complexes of platinum(II) containing η-methyleugenol

Several complexes of the formula trans-[Pt(Meug)(Am)Cl₂], Meug: methyleugenol (4-allyl-1,2-dimethoxybenzene), a η²-coordinated olefin, and Am: ammine, methylamine, diethylamine, o-toluidine, m-toluidine, p-toluidine, o-anisidine, m-anisidine and p-anisidine have been prepared. UV, IR, Raman, ¹H NMR, ¹³C NMR and 2D NMR spectra of the complexes were recorded and analyzed.     

Efficient NMR enantiodiscrimination of bridge fluorinated paracyclophanes using lanthanide tris β-diketonate complexes

A selection of amino-substituted 1,1,2,2,9,9,10,10 octafluoro[2.2]paracyclophanes were tested for enantiodiscrimination by ¹H and ¹⁹F NMR spectroscopy via their interaction with different lanthanide tris β-diketonate chiral shift reagents. The amino-, and the pseudo-ortho di-amino substituted octafluoro[2.2]paracyclophanes, both of which exhibit planar chirality, revealed significant shifts and splittings of various ¹H and ¹⁹F NMR signals upon the addition of the chiral shift reagents, which allowed the easy determination of the enantiomeric purity. When the chiral shift reagent was added to an inseparable mixture of the (chiral) pseudo-meta, and (achiral) pseudo-para diamino analogues, both the chiral and achiral molecules revealed NMR doubling. In the case of the achiral molecule, this NMR behavior is due to the meso nature of the pseudo-para species.     

P NMR study of the stoichiometry, stability and thermodynamics of new complexation between uranyl (II) nitrate and N-methyliminobis(methylenephosphonic acid) in two binary D2O-DMSO-d6 solvent mixtures

The complexation reaction between uranyl (II) nitrate, and N-methyliminobis(methylenephosphonic acid) (MIDPH) was investigated in two different binary solvent mixtures of D₂O-DMSO-d₆ at various temperatures using ³¹P NMR spectroscopy. The exchange between the free ligand and the 1:1 complexed ligand was slow on the NMR timescale and two ³¹P NMR signals were observed. The formation constant of the resulting complex was evaluated from integration of the two ³¹P NMR signals. The values of thermodynamic parameters of the resulting complex (ΔH, ΔS and ΔG) were determined from the temperature dependence of the formation constants. In the two solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized.     

NMR and DSC study of temperature-induced phase transition in aqueous solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers

Combination of ¹H NMR spectroscopy and differential scanning calorimetry (DSC) was used to investigate temperature-induced phase transition in D₂O solutions of poly(N-isopropylmethacrylamide-co-acrylamide) random copolymers. Both the NMR and DSC data showed dependence on the acrylamide (AAm) content in the copolymer; with increasing AAm content, the phase transition is shifted to higher temperatures, and both phase-separated fractions determined by NMR and change of the enthalpy determined by DSC decrease faster than the content of thermosensitive N-isopropylmethacrylamide (NIPMAm) units in the copolymer. NMR data were used to construct van't Hoff plots, and changes of the enthalpy ΔH and entropy ΔS, characterizing the phase transition, were determined. As it follows from comparison of NMR and DSC thermodynamical parameters (ΔH values), the size of the cooperative units (domains), undergoing the transition as a whole, decreases with increasing AAm content in the copolymer since the NIPMAm collapsed domains are separated by regions with hydrated AAm and surrounding NIPMAm sequences.     

Aluminum-27 NMR studies of alcoholic (2-hydroxyethyl)trimethylammonium aluminate solutions

²⁷Al NMR spectroscopy is a power tool for investigation of the aluminate species existing in both aqueous and non-aqueous solutions. Aluminum-27 nuclear magnetic resonance (NMR) spectroscopy also can be used to determine thermodynamic properties of complexes in the solution. In this report, ²⁷Al NMR spectroscopy was used to characterize species present in alkaline alcoholic aluminate solutions. (2-Hydroxyethyl)trimethylammonium (2-EHTMA) hydroxide was used as base. In solution of CH₃OH and H₂O in a mole ratio of 64:1 it was possible to detect five signals by aluminum-27 NMR, indicating formation of [Al(OH)_4−n(CH₃OH)_n]⁽ⁿ⁻¹⁾⁺ (n = 0,1, 2, 3 and 4) species. Aluminum-27 NMR spectroscopy has also used for investigation of the species present in the ethanolic 2-HETMA aluminate solutions. The equilibrium constants for the formation of aluminate complexes were also determined for both methanolic and ethanolic aluminate solutions. Aluminum-27 NMR spectra of propanolic and butanolic 2-HETMA aluminate solutions were also studied.     

Synthesis of novel pyrazole derivatives incorporating one dicarba-closo-dodecaborane unit

Boron clusters, and especially dicarba-closo-dodecaboranes, can be used as hydrophobic pharmacophores in the design of new drugs. In the current letter, analogs of the CB1 receptor inverse agonist Rimonabant incorporating a carborane cage (either ortho- or meta-carborane) have been synthesized in moderate yields and their structure has been elucidated by means of ¹H NMR, ¹³C NMR, ¹¹B NMR, and HPLC-MS.     

31P NMR in wood chemistry: A review of recent progress

Over the past few years substantial efforts in our laboratory have been devoted toward the development of novel NMR techniques for the analysis of soluble and solid lignocellulosic substances. These efforts were undertaken in order to expand the frontiers of application of NMR for the detection of functional groups present in such materials. Our methodology involves the selective phosphorus-tagging of a variety of functional groups present in lignin and carbohydrates, followed by solution and solid state³¹P NMR spectroscopies. This paper attempts to review the status of this technique by discussing its development for the analysis of soluble and solid lignocellulosic samples. Solution³¹P NMR can be used to examine soluble lignin and carbohydrate samples after phosphitylation with 1,3,2 dioxaphospholanyl chloride. This is a novel and powerful means to determine the three principal forms of phenolic hydroxyls present in ligninsi.e. p-hydroxyphenyl, guaiacyl, and syringyl structures. In addition, primary hydroxyls, carboxylic acids, and the two diastereomeric forms of arylglycerol-beta-aryl ether units (β-O-4 structures) present in lignins can also be determined from a single³¹P NMR experiment. When applied to carbohydrates, the technique gave characteristic signals for thealpha andbeta anomers and the epimeric forms of monosaccharides. Completely resolved³¹P NMR spectra were also obtained when lignin-carbohydrate model compounds were examined. Solid state³¹P NMR can be used to determine quinone chromophore groups present in solid lignocellulosic samples. The method is based on literature accounts that describe adduct formation between trimethyl phosphite and quinones followed by solid state³¹P NMR. This reaction when reexamined in our laboratory showed that the presence of carboxylic acids in high yield pulps significantly affected the solid state³¹P NMR signal intensity. This realization permitted the development of an experimental protocol that allowed solid state³¹P NMR signals to be received from high yield pulps that contain information only onortho-quinones and coniferaldehyde chromophores. It was thus found that about 0.7ortho-quinone groups are present in every 100 C₉ units within the lignin of a black spruce refiner mechanical pulp sample, in agreement with previously applied independent techniques.     

Intramolecular mobility of pentacoordinated tin compounds

The ¹¹⁹Sn NMR and ¹³C NMR data are reported for N-alkyl-5,5-di-t-butyldiptychoxazstannolidines. The activation parameters of an intramolecular process are estimated from the temperature dependence of the ¹H NMR spectra in different polar solvents, The NMR data support the dissociation—inversion mechanism for this process.     

Carbon-13 NMR study of some acetylenic amines,the N-oxides and their rearrangement products

Carbon-13 NMR chemical shifts of some N, N-dialkyl-4-acetoxybut-2-ynylamines and their corresponding N-oxides have been analysed. These N-oxides undergo thermal rearrangement to O-allenyl hydroxylamine for which the ¹³C NMR spectral assignments were also carried out. The effect of N-oxidation on the chemical shifts is calculated.     

Facile preparation of a symmetric hexavalent oleanolic acid/per-O-methylated α-cyclodextrin conjugate with two conformations in solution and unambiguous NMR analysis

A newly synthesized hexavalent oleanolic acid/per-O-methylated α-cyclodextrin conjugate shows significant differences in NMR spectra with previously synthesized analogs. Characterization of the product by ¹H NMR, ¹³C NMR, COSY, HSQC, HMBC, TOCSY, NOE, and ROESY experiments were performed. Detailed investigations revealed that the compound has two conformations in solution and the ratio of them was 1:1. Further variable-temperature NMR study revealed that the two conformations were stable at temperature range of 273–323 K in CDCl₃ solution.     

Synthesis and NMR spectra of the syn and anti isomers of substituted cyclobutanes—evidence for steric and spatial hyperconjugative interactions

The syn and anti isomers of cis,cis-tricyclo[5.3.0.0^2,6]dec-3-ene derivatives have been synthesized and their ¹H and ¹³C NMR spectra unequivocally analyzed. Both their structures and their ¹H and ¹³C NMR chemical shifts were calculated by DFT, the latter two calculations employing the GIAO perturbation method. Additionally, calculated NMR shielding values were partitioned into Lewis and non-Lewis contributions from the bonds and lone pairs involved in the molecules by accompanying NBO and NCS analyses. The differences between the syn and anti isomers were evaluated with respect to steric and spatial hyperconjugation interactions.     

Pyridine-1-oxide complexes of lanthanide iodides

Pyridine-1-oxide complexes of lanthanide iodides of the formulaLn(PyO)₈I₃ whereLn=La, Pr, Nd, Tb, Dy, Er, and Yb have been prepared and characterised by analyses, molecular weight, conductance, infrared and proton NMR data. Proton NMR and IR data have shown the coordination of the ligand to the metal through the oxygen atom of the N?O group. NMR data have been interpreted in terms of a distorted square antiprismatic geometry in solution.     

Chemotaxonomy of the rutaceae—XII: The occurrence of severine in Atalantia monophylla and Hesperethusa crenulata. A revised structure for severine

Severine palmitate has been isolated from the fruit of Atalantiamonophylla and Hesptrethusacrenulata both of the family Rutaceae. NMR shift reagent and mass spectral studies suggest the need for revision of the structure of severine to 2. The revised structure is confirmed by the ¹³C NMR spectra of severine and its derivatives.     

H/P NMR pH indicator series to eliminate the glass electrode in NMR spectroscopic pKa determinations

NMR titration is an efficient method to determine pK_a values of multiprotic acids in aqueous solution. While modern 1D/2D NMR techniques yield chemical shifts with increasing precision, the glass electrode-based pH measurement becomes the limiting factor to affect the precision of the resulting dissociation constants. The pH in the NMR tube can also be deduced from the actual chemical shift of an appropriate monoprotic indicator molecule. In the present work, the in situ NMR pH measurement has been extended for the entire pH range 0-12 using indicators with overlapping ranges of dissociation. In the first, calibrating ¹H/³¹P NMR titration, limiting chemical shifts and pK were determined for each indicator. An analysis of error propagation showed that the accuracy and precision of glass electrodes can be achieved at 1.8 < pH < 12 and even exceeded at pH extremes by NMR indicators, respectively. The assembled set of indicators was applied for in situ pH monitoring in the following “electrodeless” ¹H/³¹P NMR titration of a newly synthesized aminophosphinophosphonic acid. Multivariate nonlinear parameter estimation was used to calculate the pK values that were confirmed by potentiometric titrations.     

Multilevel profiling and identification of Dalbergia odorifera and Dalbergia stevensonii by FTIR,NMR and GC/MS

Chemical differences of the extractives revealed by FTIR methods can be further confirmed by ¹H NMR and ¹³C NMR. Meanwhile, the volatile compounds in the extractives can be identified by GC/MS     

Isolation, synthesis and structure confirmation of the impurity in crude roflumilast product

An impurity was isolated from crude synthesized roflumilast and characterized by ¹H NMR, ¹³C NMR, and HR-MS, which confirmed the structure as N-(3,5-dichloropyrid-4-yl)-4-difluoromethoxy-3-hydroxybenzamide. To further verify the structure, this compound was synthesized from 4-difluoromethoxy-3-hydroxybenzaldehyde. Comparison of the ¹H NMR, ¹³C NMR, HR-MS, and the HPLC spectrum of the impurity and the authentic sample indicated that this impurity was N-(3,5-dichloropyrid-4-yl)-4-difluoromethoxy-3-hydroxybenzamide. This demonstrated the significance of monitoring the reaction process of roflumilast.