Multinuclear magnetic resonance analysis of 2-(trifluoromethyl)-2-oxazoline

(1)H, (19)F, (13)C, (15)N, and (17)O NMR chemical shifts and (1)H-(1)H, (1)H-(19)F, (1)H-(13)C, (19)F-(13)C, and (19)F-(15)N coupling constants are reported for 2-(trifluoromethyl)-2-oxazoline.     

Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4-benzotriazine N-oxides

1H, 13C and 15N NMR measurements (1D and 2D including 1H--15N gs-HMBC) have been carried out on 3-amino-1, 2,4-benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311+G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-benzotriazines.     

Optimizing sensitivity and resolution in time-shared NMR experiments

An improved approach to optimize the overall sensitivity and the resolution requirements in the indirect dimension of (13)C/(15)N time-shared (TS) NMR experiments is presented. A different data sampling acquisition procedure is applied for (13)C and (15)N in the indirect dimension, and a proper data recombination before conventional data processing allows a customized adjustment of spectral widths, number of scans and number of increments individually for (13)C and (15)N. The major benefit is an important improvement on the detection limits of the TS experiment that overcomes the lower sensitivity of (15)N over (13)C at natural abundance. We evaluate such enhancements from 2D TS-HMBC experiments recorded on a nitrogen-containing synthetic azole derivative of pharmaceutical interest.     

A 1H, 13C and 15N NMR study in solution and in the solid state of six N-substituted pyrazoles and indazoles

Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed.     

Complete assignment of the 1H, 13C, 15N and 19F NMR spectra of nine DL-phenylalcoholamide anticonvulsants

The 1H, 13C, 15N and 19F NMR spectra of nine DL-phenylalcoholamides bearing fluorine and chlorine as substituents of the phenyl ring are reported. All of them are active as anticonvulsants in pentylenetetrazole-induced seizures.     

Improved method for unambiguous amino acid side-chain 1H and 13C resonance assignment

Side-chain proton and carbon-13 resonance assignments of [13C;15N]-enriched proteins usually rely on combinations of several multi-dimensional experiments. Here, we describe a four-dimensional pulse sequence, H(C)C-COSY-TOCSY-(CACO)NH, which provides the information required to assign completely aliphatic side-chain resonance frequencies. As in widely used HCC(CO)NH-TOCSY experiments, problems due to spectral crowding are alleviated by exploiting the dispersion of backbone amide 1H and 15N signals. The modification introduced here allows signals from different side-chains to be distinguished even in the case of overlap in the 1H(N)-15N plane of the spectra. For illustration, the new method is applied to two proteins with molecular masses of 11 and 23 kDa.     

Statistical analysis of (13)C and (15)N NMR chemical shifts from GIAO/B3LYP/6-311 + + G** calculated absolute shieldings

The (13)C and (15)N absolute shieldings of 28 compounds have been calculated at the GIAO/B3LYP/6-311 + + G** level to complete a collection of data already published. This has allowed us to devise new equations relating delta and sigma for these nuclei based on 461 points ((13)C) and 70(72) points ((15)N).     

Study of stereospecificity of 1H, 13C, 15N and 77Se shielding constants in the configurational isomers of the selenophene-2-carbaldehyde azine by NMR spectroscopy and MP2-GIAO calculations

In the (1)H and (13)C NMR spectra of selenophene-2-carbaldehyde azine, the (1)H-5, (13)C-3 and (13)C-5 signals of the selenophene ring are shifted to higher frequencies, whereas those of the (1)H-1, (13)C-1, (13)C-2 and (13)C-4 are shifted to lower frequencies on going from the EE to ZZ isomer or from the E moiety to the Z moiety of EZ isomer. The (15)N chemical shift is significantly larger in the EE isomer relative to the ZZ isomer and in the E moiety relative to the Z moiety of EZ isomer. A very pronounced difference (60-65 mg/g) between the (77)Se resonance positions is revealed in the studied azine isomers, the (77)Se peak being shifted to higher frequencies in the ZZ isomer and in the Z moiety of EZ isomer. The trends in the changes of the measured chemical shifts are reasonably reproduced by the GIAO calculations at the MP2 level of the (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of both selenophene rings relative to the C = N groups. The NBO analysis suggests that such an arrangement of the selenophene rings may take place because of a higher energy of some intramolecular interactions.     

Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations

NMR spectroscopic studies are undertaken with derivatives of 2‐pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts (¹H, ¹³C, ¹⁵N) and coupling constants (¹H,¹H; ¹³C,¹H; ¹⁵N,¹H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of ¹³C,¹H spin coupling constants is accomplished by 2D (δ,J) long‐range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3‐hydroxy‐2‐pyrazinecarboxylic acid are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Substituent effects on (15)N and (13)C NMR chemical shifts of 5-phenyl-1,3,4-oxathiazol-2-ones: a theoretical and spectroscopic study

The synthesis and assignment of (15)N and (13)C NMR signals of the 1,3,4-oxathiazol-2-one ring in a series of para-substituted 5-phenyl derivatives are reported. DFT calculations of (15)N and (13)C chemical shifts correspond closely to observed values. Substituent effects are interpreted in terms of the Hammett correlation and calculated bond orders.     

1H, 13C and 15N NMR spectra of ciprofloxacin

1H NMR assignment, including the values of delta(H) and J(H,H) for the cyclopropane moiety, and 13C NMR and 15N NMR spectral data for ciprofloxacin are presented.     

Experimental and quantum-chemical studies of 1H, 13C and 15N NMR coordination shifts in Pd(II) and Pt(II) chloride complexes with quinoline, isoquinoline, and 2,2'-biquinoline

1H, 13C, and 15N NMR studies of platinide(II) (M=Pd, Pt) chloride complexes with quinolines (L=quinoline-quin, or isoquinoline-isoquin; LL=2,2'-biquinoline-bquin), having the general formulae trans-/cis-[ML2Cl2] and [M(LL)Cl2], were performed and the respective chemical shifts (delta1H, delta13C, delta15N) reported. 1H coordination shifts of various signs and magnitudes (Delta1Hcoord=delta1Hcomplex-delta1Hligand) are discussed in relation to the changes of diamagnetic contribution to the relevant 1H shielding constants. The comparison to the literature data for similar complexes containing auxiliary ligands other than chlorides exhibited a large dependence of delta1H parameters on electron density variations and ring-current effects (inductive and anisotropic phenomena). The influence of deviations from planarity, concerning either MN2Cl2 chromophores or azine ring systems, revealed by the known X-ray structures of [Pd(bquin)Cl2] and [Pt(bquin)Cl2], is discussed in respect to 1H NMR spectra. 15N coordination shifts (Delta15Ncoord=delta15Ncomplex-delta15Nligand) of ca. 78-100 ppm (to lower frequency) are attributed mainly to the decrease of the absolute value of paramagnetic contribution in the relevant 15N shielding constants, this phenomenon being noticeably dependent on the type of a platinide metal and coordination sphere geometry. The absolute magnitude of Delta15Ncoord parameter increased by ca 15 ppm upon Pd(II)-->Pt(II) replacement but decreased by ca. 15 ppm following trans-->cis transition. Experimental 1H, 13C, 15N NMR chemical shifts are compared to those quantum-chemically calculated by B3LYP/LanL2DZ+6-31G**//B3LYP/LanL2DZ+6-31G*, both in vacuo and in CHCl3 or DMF solution.     

1H, 13C and 15N NMR spectral characterization of twenty-seven 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-ones

1H, 13C and 15N NMR chemical shifts and couplings (n)J(H,C) in DMSO-d(6) at 30 degrees C have been determined for 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-one derivatives 1-27. Their chemical shift assignments are based on PFG DQF 1H,1H COSY, PFG 1H,13C HMQC as well as PFG 1H,13C and 1H,15N HMBC experiments. For compounds 1-10 including aryl fluorine substituent(s) also the couplings (n)J(F,C) (n = 1 - 4) are reported.     

^1^5N标记邻位芳香羟肟配位体的核磁共振研究

利用稳定同位素的磁性和质量同位素效应已成为研究有机结构化学的重要手段。我们为研究部位芳香及其芝渡金属如Cu(Ⅱ),Ni(Ⅱ),Co(Ⅱ),Fe(Ⅱ)配合物的光     

Effects of polymorphic differences for sulfanilamide, as seen through 13C and 15N solid-state NMR, together with shielding calculations

We recorded both carbon-13 and nitrogen-15 NMR spectra of the three solid forms of sulfanilamide most commonly known. This study led to an interpretation of the solid-state effects seen in cross-polarization magic angle spinning spectra. Relaxation times for the different forms were measured. These show different behaviour for the three forms, arising from mobility variations. To obtain information on local environments, static spectra and spinning sideband manifolds were recorded and analysed for the 15N resonances, using isotopically enriched samples. Shielding asymmetries and anisotropies for the two nitrogen nuclei were obtained, showing very different behaviour for the two sites. Shielding calculations were carried out for both 13C and 15N nuclei, and the results are discussed in relation to the experimental values.     

1H, 13C and 15N NMR coordination shifts in gold(III), cobalt(III), rhodium(III) chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline

Au(III), Co(III) and Rh(III) chloride complexes with pyridine (py), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) of the general formulae [M1LCl3], trans-[M2L4Cl2]+, mer-[M2L3Cl3], [M1(LL)Cl2]+, cis-[M2(LL)2Cl2]+, where M1=Au; M2=Co, Rh; L=py; LL=bpy, phen, were studied by 1H--13C HMBC and 1H--15N HMQC/HSQC. The 1H, 13C and 15N coordination shifts (the latter from ca-78 to ca-107 ppm) are discussed in relation to the type of metal, electron configuration, coordination sphere geometry and the type of ligand. The 13C and 15N chemical shifts were also calculated by quantum-chemical NMR methods, which reproduced well the experimental tendencies concerning the coordination sphere geometry and the ligand type.     

13C and 15N NMR chemical shifts of 1-(2',4'-dinitrophenyl) and 1-(2',4',6'-trinitrophenyl) pyrazoles in the solid state and in solution

The (13)C and (15)N CPMAS NMR spectra of 18 pyrazoles substituted at position 1 by dinitrophenyl and trinitrophenyl (picryl) groups have been recorded. To help in the assignments, some of these compounds were studied in DMSO-d(6) solution. Phenomena such as the conformation of the N-aryl groups and broadening of splittings due to quadrupolar nuclei are discussed.     

Stereochemical analysis of N-cyclohexylidene-N-(1-phenylethyl)amine derivatives

The configurational properties of a series of cyclohexylidene imines are discussed on the basis of their 1H, 13C and 15N NMR spectral data.     

The impact of the pi-electron conjugation on (15)N, (13)C and (1)H NMR chemical shifts in push-pull benzothiazolium salts. Experimental and theoretical study

The (15)N as well as (13)C and (1)H chemical shifts of eight push-pull benzothiazolium iodides with various pi-conjugated chains between dimethylamino group and benzothiazolium moiety have been determined by NMR spectroscopy at the natural-abundance level of all nuclei in DMSO-d(6) solution. In general, the quaternary benzothiazolium nitrogen is more shielded [delta((15)N-3) vary between - 241.3 and - 201.9 ppm] with respect to parent 3-methylbenzothiazolium iodide [delta((15)N-3) = - 183.8 ppm], depending on the length and constitution of the pi-conjugated bridge. A larger variation in (15)N chemical shifts is observed on dimethylamino nitrogen, which covers the range of - 323.3 to - 257.2 ppm. The effect of pi-conjugation degree has a less pronounced influence on (13)C and (1)H chemical shifts. Experimental data are interpreted by means of density functional theory (DFT) calculations. Reasonable agreement between theoretical and experimental (15)N NMR chemical shifts was found, particularly when performing calculations with hybrid exchange-correlation functionals. A better accord with experiment is achieved by utilizing a polarizable continuum model (PCM) along with an explicit treatment of hydrogen-bonding between the solute and the water present in dimethylsulfoxide (DMSO). Finally, (13)C and (1)H NMR spectra were computed and analysed in order to compare them with available experimental data.