Identification of some isomeric 3,5-unsymmetrically substituted 1-aroyl-pyrazole derivatives by NMR spectroscopy

The ¹H and ¹³C nmr chemical shifts are used for the structural assignment of isomeric 1-aroyl-4,5-dihydro-5-hydroxy-4,4-dimethyl-1H-pyrazoles 1 unsymmetrically substituted with phenyl or methyl in the 3,5-positions of the pyrazole ring. The ¹H nmr spectra of 1-aroyl- or 1-acetyl-4-methyl-1H-pyrazoles 2 are useful in structure elucidation of unsymmetrically 3- or 5-methyl substituted derivatives.     

Investigation of substituted 1,3-oxazolidines using 1H and 13C NMR spectroscopy

The characteristics of the ¹H and ¹³C NMR spectra of 1,3-oxazolidines with substituents in the 2-, 3-, and 5-positions have been studied. The relation of the spectral characteristics to the structure and configuration of the compounds has been examined, and information on the transmission of the substituent effect through the atoms of nitrogen and oxygen has been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1255–1260, September, 1986.     

1H AND 13C NMR SPECTRA OF 1-DEOXY-1-THIOGLYCOPYRANOSIDES

Abstract

In the absence of previous systematic investigations, we have embarked on the study of the NMR spectra of thioglycosides, as we needed structural information in connection with our work on the spectroscopic properties of these compounds. In this sommunication, data will be presented on alkyl α - and β-thiogluco- and -thiogalactopyranosides and some related compounds, including certain natural products like lincomycin, sinigrin, and glucocapparin. The ¹H spectra of the strongly coupled carbohydrate portion can readily be analyzed at 270 MHz in the case of the thiogalactosides, whereas the spectrum of the thioglucose moiety in, e.g., thioglucose sodium salt, remains a system of higher order even at 360 MHz, giving rise to multiple lines and virtual coupling. The assignment of the ¹³ spectra proceeded basically via selective or via frequency dependant off-resonance heteronuclear double resonance experiments at 68 MHz; the C-H coupling pattern (triplet) directly reveals the position of C-(6). Application of the increment method of the ¹³C chemical shift in connection with the thioalkyl grouping presented no complications. Tetraacetylation of the thioglycosides shifts the ring ¹³C resonances in a systematic manner and is, therefore, an additional aid. All the compounds investigated adopt the ⁴C₁ conformation; in the α-series, ³J(H-1/H-2) = ca. 5.5 Hz, i.e., relatively large. Long range ¹³C- ¹H coupling constants were measured in a few cases only. Values of ¹J (¹³C- ¹H) were also obtained from satellite lines in the appropriate high-field ¹H spectra. From the spectra of the fully or partly analyzed compounds rules can be deduced that are especially helpful in the examination of ¹³C spectra of other thioglycosides, employing, e.g., chemical shift data, coupling constants, and T₁ data.     

Synthesis, NMR and X-ray characterisation of 6-substituted 4-amino-5-aryldiazenyl-1-arylpyridazinium salts

A new simple method has been used to prepare 6-substituted 4-(subst. amino)-5-aryldiazenyl-1-arylpyridazinium salts from N-methyl- or N-aryl-3-amino-1-phenylbut-2-en-1-ones and 4-aminopent-3-en-2-ones and substituted benzenediazonium tetrafluoroborates or hexafluorophosphates. The structure of selected derivatives was studied by means of ¹⁵N NMR spectra and X-ray.     

Synthesis and 13C NMR of (trifluoromethyl)hydroxypyrazoles

Reaction of ethyl 4,4,4-trifluoroacetoacetate with methylhydrazine produced not only the previously reported 5-hydroxy-3-(trifluoromethyl)pyrazole 1 but also its unknown isomer the 3-hydroxy-5-(trifluoromethyl)pyrazole 4 . The structure assignments are established based on ¹³C nmr spectra. Compound 1 was converted to 5-chloro-3-(trifluoromethyl)pyrazolecarboxylic acid 3 in two steps.     

13C NMR spectra of some 1-, 3- and 4-monosubstituted and disubstituted isoquinolines

Chemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso-quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of ¹³C resonances were based on the spectra of the corresponding 5-deutero derivatives. For the fluoroisoquinolines some ¹³CF coupling constants are given. The ¹³C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4- and 1,4-disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS effects.     

Electron density distributions in substituted 2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-dienes studied by NMR spectroscopy

The signals in the¹³C NMR spectra of 2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-dienes (R¹=R²=H, Me,cyclo-C₃H₅, SiMe₃, SnMe₃, R¹=Me, R²=H, Cl) were completely assigned using 2D NMR spectroscopy. The pattern of the variation of the chemical shifts in the¹³C NMR spectra indicates that the effects of substituents R¹ and R² on the heterocycle and on the phenyl groups are of inductive rather than mesomeric origin and include the direct through-space polarization of bonds (field effect). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1962–1965, November, 1997.     

Carbon-13 NMR study of some isomeric n-nitroindazole derivatives

The ¹³C NMR spectra of 1,5- and 2,x-dinitroindazoles “x=4-7” and 3-bromo-1,x-dinitroindazoles are recorded and discussed. The data on he 2,x-dinitroindazoles confirm our previous structurea assignment based on ¹H NMR spectroscopy. The ¹³C NMR spectra established that in the novel 3-bromo-1,x-dinitroindazoles the N-nitro group is attached at N-1.     

Dynamic 1H NMR spectroscopy of η2-ethylene transition metal complexes

The low-temperature ¹H NMR spectra of bis(ethylene)trimethylphosphinenickel (1), η⁵-cyclopentadienyl(ethylene)methylnickel (2a), bis(ethylene)-η⁵-cyclopentadienylcobalt (2b), [bis(1-ethyl-2,4,6-triphenylphosphorinyl)nickel]P,P′-nickel(ethylene) (3) and η⁵-cyclopentadienyl(ethylene)hydrido(triphenylphosphine)ruthenium (4) exhibit {AA′B′B} (1) {ABB′A} (2a and 2b), {ABA′B′} (3) or {ABCD} (4) spin patterns, respectively, for the complexed ethylene. A full line shape analysis including all the proton couplings was performed for the ethylene rotation in 1, 2a and 2b. In addition to olefin rotation, a reversible intramolecular β-H-elimination was confirmed for 4 by magnetization transfer experiments.     

The assignment of the 1H NMR signals to the methine bridge H-atoms in chlorophyll derivatives

Experiments are described which prove the assignments of the α- and β-protons in the ¹H NMR spectra of methyl phaeophorbide a ( 1 ) and methyl pyrophaeophorbide a ( 2 ). Because of the structural relationship between derivatives of the bacteriochlorophylls d ( 5 ) and 2 , dehydration of 5 results in a homologue mixture [2-(des-α-hydroxyethyl)-2-vinyl-bacteriomethyl phaeophorbide] d ( 6 ) of 2. Since the homologue substituents in 6 are located at C-4 and C-5 surrounding the β-H position, and since only one broad signal appears in its ¹H NMR spectrum, this is assigned to the β-proton. This experiment proves that the sequence of increasing shielding is β, α and δ in 6 ; and, therefore, the same sequence applies to the ¹H NMR spectra of 1 and 2 . This knowledge reveals that the product of electrochemical reduction of 1 in deuteromethanol is exclusively an α-chlorin-phlorin ( 8 ). In addition, the ¹H NMR spectrum of the 2-vinyl derivatives of the bacteriomethyl phaeophorbides c ( 7 ) shows the same broad signal at lowest field as does that of 6 . The sequence of increasing shielding is therefore, β, α. The influence of the additional δ-methyl group in 7 on the ring current is explained.     

A fast MAS 1H NMR study of amino acids and proteins

Fast sample spinning (up to 32 kHz) in tandem with delayed acquisition enabled resolved ¹H NMR spectra of solid amino acids to be recorded. The resulting spectra are, however, significantly dependent on sample crystallinity and on sample preparation conditions, e.g. sample drying. Sample heating leads to a marked increase in signal to noise ratio and enables groups with different dynamic properties to be identified. In addition, the observation of peak shifts as a function of heating allows the identification of hydrogen bonded sites. Spectral assignment of the ¹H MAS spectra is proposed for some examples based on relaxation properties, study of deuteriated samples and 2D NMR. The effects of molecular weight and sample complexity on the ¹H MAS spectra were investigated using tetraglycine, polyglycine and two proteins: a small protein (lysozyme) and a much larger protein (a cereal storage protein named high molecular weight subunit 1Dx5). Moderate spectral resolution was achieved for the peptides and lysozyme, but for 1Dx5, significant resolution enhancement was obtained enabling the identification of resonances in all regions of the spectra including the alpha region, the aromatic region and the NH backbone region.     

SEC‐MR‐NMR: Online Coupling of Size Exclusion Chromatography and Medium Resolution NMR Spectroscopy

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC‐MR‐NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table‐top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online ¹H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. ¹H NMR spectra of PMMA and PS homopolymers as well as PS‐PMMA block copolymers were of sufficient quality to enable detection and de‐formulation of unknown polymer compounds. ¹H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC‐MR‐NMR combination.

     

Synthesis and NMR Characterization of 2,5-Bis(Trimethylsilyl)-3,4-Diphenyl-1-Silacyclopentadienyl Dianion

Abstract

Two new silyl-substituted silolide dianions (11a, 11b) have been synthesized and characterized spectroscopically. Their ¹H, ²⁹Si, and ¹³C NMR spectra show similarities to the known phenyl- and alkyl-substituted analogues. Reaction with ethyl bromide gave the expected diethylsilol. B3LYP/6-31 + G* geometry optimization revealed equalized CC distances, and also NICS values indicate significant aromaticity.

Figures S1—S5 are available online in Supplemental Materials.     

Carbon-13 NMR spectra of monosubstituted pyrazines

Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the ¹³C NMR spectra are generally quite similar to those in the ¹H NMR spectra. The ¹³C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the ¹³C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.     

The effects of morphology on 1H NMR spectra and relaxation in semicrystalline polyolefins

A brief résumé is given of the role of structural heterogeneity, magnetic dipolar couplings, molecular structure, and molecular motion in determining the ¹H NMR spectra and relaxation properties of heterogeneous solids such as semicrystalline polymers. Measurements of ¹H spin-lattice relaxation in laboratory (T₁) and rotating frames (T) are reported for a number of solid polyolefin samples. These include solution-crystallized and melt-crystallized polyethylene, annealed and quenched isotactic polypropene, and isotactic polybut-1-ene. In addition, broad-line ¹H spectra, both normal and partially (T) relaxed, are reported for these materials as well as a number of pulsed NMR experiments having the philosophy of the so-called Goldman–Shen experiment. Spin-lattice relaxation (T₁) for all samples is a single exponential process, whereas rotating-frame relaxation comprises three exponential processes both on-resonance (θ = 90°) and off-resonance at the magic angle (θ = 54.7°), with the latter generally being much slower. The spectra show clearly the existence of components having differing degrees of mobility and, with the exception of the solution-crystallized polyethylene, the partially (T) relaxed spectra indicate a correlation between breadth of resonance line and magnitude of T_1ρ. The Goldman–Shen-type experiments indicate a spin-diffusional transport of magnetization between the different spectral and (T) components. A computer program has been used to simulate the NMR behavior of a three-region system comprising repeating units of infinite lamellae of different widths, each region having different intrinsic relaxation times and spin diffusion coefficients. The results demonstrate that the observed ¹H NMR behavior of these samples can be interpreted in terms of this model and that, inter alia, the long-time T behavior reflects, qualitatively, the time taken for magnetization to diffuse a distance of the order of the dimensions of the region to which it corresponds.     

Mannich reaction on 2-(2-benzofuranyl)-1H-indole. Determination of structure by NMR spectroscopic techniques

Analysis of the product from the Mannich reaction of 2-(2-benzofuranyl)-1H-indole via ¹H and ¹³C nmr spectroscopy was performed. The studies included use of Pr(Fod)₃ shift reagent, proton-coupled ¹³C spectra, deuterium isotope induced shifts and protonation studies. It was found that the reaction occurred on the indole moiety at C-3.     

New N-(Arylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes. Synthesis, 1H and 13C NMR Spectra,and Chemical Reactions

A synthesis of new N-(arylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes obtained by reaction of stereoisomeric exo- and endo-5-aminomethylbicyclo[2.2.1]hept-2-enes with arylsulfonyl chlorides is described. With the use of the data of ¹H and ¹³C NMR spectra, including those of two-dimensional spectra recorded in COSY and NOESY mode, the contribution of stereochemical features of sulfonamides into the spectra structure of endo- and exo-isomers was evaluated. Applying various methods of the phase-transfer catalysis alkylation and acylation of the stereoisomeric arylsulfonamides containing a norbornene fragment was carried out. The reactions of alkylated stereoisomeric sulfonamides, N-(benzyl)-N-(3,4-dichlorophenylsulfonyl)-5-aminomethylbicyclo[2.2.1]hept-2-enes, with peroxyphthalic acid provide epoxides; the orientation of substituents in the cage norbornene fragment does not affect the direction of the process. The structure of the products obtained by sulfonamides transformations was confirmed by IR, ¹H and ¹³C NMR spectra.     

Characterization of tri-o-methylcellulose by one- and two-dimensional NMR methods

Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts (¹H and ¹³C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional ¹H and ¹³C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton–proton correlation spectroscopy (¹H, ¹H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the ¹³C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (J_H,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the ¹H and ¹³C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D -glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the ¹H and ¹³C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A ≪ H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 ≪ C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the ⁴C₁ arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J_5,6A and J_5,6B) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution. © 1999 John Wiley & Sons, Inc.* J Polym Sci A: Polym Chem 37: 4019–4032, 1999     

High resolution 13C and 1H NMR spectral analysis of 1-azafluorene

An analysis of the ¹H and ¹³C spectra of 1-azafluorene has been carried out using computer calculations and homo- and heteronuclear double resonance techniques. The ⁴J, ⁵J and ⁶J long-range coupling constants of the 9-CH₂ group protons with the protons of the pyridine and the phenylene rings have been observed and measured. The long-range J(CH) values in the ¹H coupled ¹³C spectrum have been assigned and measured on a first-order basis.     

13C NMR spectra of some 1,2-disubstitutedN-vinyl-1H-1,2,4-triazoles

¹³C NMR spectra (20 and 75 MHz, in DMSO-d₆) of a series of 1,3-diaryl-3-(1H-1,2,4-triazol-1-yl)- and 1,3-diaryl-2-(1H-1,2,4-triazol-1-yl)prop-2-en-1-ones were registered. It was shown that the chemical shifts of both the carbon atom of the alkene group and C(3) reflect regio- and stereoisomerism of these compounds. Taking this into account the isomeric structures of several 1,3-diaryl-3-(1H-1,2,4-triazol-1-yl)prop-2-en-1-ones were identified and the configurations relative to the double bond of a number of 1,3-diaryl-2-(1H-1,2,4-triazol-1-yl)prop-2-en-1-ones were determined.