Study on 15N NMR of lithium sudan I complex

The ¹⁵N chemical shift have been measured for α-¹⁵N-labelled phenylazo-2-naphthol and its lithium complex. The change of the ¹⁵N chemical shift on coordination of the azo nitrogen to lithium appears to be related to those of protonation of the same nitrogen. The chemical shifts of azo form and hydrazone form have been calculated according to the weighted δ_N and ¹J_NH of different fractions. It is concluded that there is a bond formation between Li and N atoms.     

13C NMR spectra of non-labelled and 15N-mono-labelled azo dyes

¹³C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4-hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2-hydroxy-5-tert-butylazobenzene) and an equilibrium mixture of both the tautomers of 1-phenylazo-2-naphthol. The absolute values of the J(¹⁵N¹³C) coupling constants have been determined by recording the spectra of the ¹⁵N isotopomers, and have been used, in some cases, for ¹³C signal assignment. A relationship has been found between the chemical shifts of the C-1′ to C-4′ carbons of the phenyl group (from the benzenediazonium ion) or the ¹J(¹⁵N¹³C) coupling constant, and the composition of the tautomeric mixture.     

Substitution effects in the 15N NMR chemical shifts of heterocyclic azines evaluated at the GIAO‐DFT level

A systematic study of the accuracy factors for the computation of ¹⁵N NMR chemical shifts in comparison with available experiment in the series of 72 diverse heterocyclic azines substituted with a classical series of substituents (CH₃, F, Cl, Br, NH₂, OCH₃, SCH₃, COCH₃, CONH₂, COOH, and CN) providing marked electronic σ‐ and π‐electronic effects and strongly affecting ¹⁵N NMR chemical shifts is performed. The best computational scheme for heterocyclic azines at the DFT level was found to be KT3/pcS‐3//pc‐2 (IEF‐PCM). A vast amount of unknown ¹⁵N NMR chemical shifts was predicted using the best computational protocol for substituted heterocyclic azines, especially for trizine, tetrazine, and pentazine where experimental ¹⁵N NMR chemical shifts are almost totally unknown throughout the series. It was found that substitution effects in the classical series of substituents providing typical σ‐ and π‐electronic effects followed the expected trends, as derived from the correlations of experimental and calculated ¹⁵N NMR chemical shifts with Swain–Lupton's F and R constants.     

13C and 15N spin–lattice relaxation and chemical shift studies of pentane-2,4-diamine

¹³C and ¹⁵N NMR chemical shift and spin–lattice relaxation data have been measured for both meso- and racemic-pentane-2,4-diamine. At high pH (12), relaxation is consistent with hindered rotation of the NH₂ group due, in part, to the formation of intramolecular hydrogen bonds. At low pH (2), relaxation is consistent with relatively unhindered rotation of the NH₃⁺ group. Rotational jump rates and barriers are reported, determined from the NT₁ ratios between ¹⁵N and ¹³C nuclei. In all cases, the ratios for the racemic diastereomer are higher than those of the meso compounds; this is interpreted in terms of conformationally more stable intramolecular hydrogen bond formation in the meso compound. Chemical shifts for the diastereomeric amines show that ¹⁵N shifts move downfield on protonation along with methyl and methylene carbons, while the methine carbon resonances move upfield.     

Tetrazoloazines. 15N nuclear magnetic resonance and infrared absorption spectroscopy

The reaction of 4-chloro-2-phenylquinazoline with K¹⁵NN₂ has been studied by ¹⁵N-NMR. spectroscopy. ¹⁵N-chemical shifts in 5-phenyl-1 (3)-[¹⁵N]-tetrazolo[1,5-c]quinazoline and -Nα(Nγ)-[¹⁵N]-4-azido-2-phenylquinazoline are reported. The characteristic IR. absorption frequencies of the tetrazole group have been determined in a series of annelated ¹⁵N-labelled compounds. From these studies and the chemistry of the labelled tetrazoles, it is concluded that all haloazines examined react with KN₃ by the direct nucleophilic substitution mechanism. An addition of nucleophile-ring opening-ring closure (ANRORC) mechanism was not observed. The synthesis of several ¹⁵N-labelled tetrazoloazines is described.     

Observation of Diastereotopic Signals in 15N NMR Spectroscopy

The first example in the literature of a compound showing anisochronous ¹⁵N atoms resulting from diastereotopicity is described. Racemic 1,3‐dimethyl‐2‐phenyloctahydro‐1H‐benzimidazole was prepared and studied by ¹H, ¹³C and ¹⁵N NMR spectroscopy. If convenient conditions were used (monitored by theoretical calculations of ²J_N‐H spin–spin coupling constants), two ¹⁵N NMR signals were observed and corresponded to the diastereotopic atoms. GIAO/density‐functional calculations of chemical shifts were not only in good agreement with the experimental values but also served as prediction tools. This study suggests that ¹⁵N NMR spectroscopy could be used to probe chirality.     

13C-NMR study on the tautomerism of 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines between the hydrazone imine and diazenylenamine forms

The ¹³C-nmr study was carried out for the tautomerism of the 3-(arylhydrazono)methyl-2-oxo-1,2-dihy-droquinoxalines 1a-g and 2a-e between the hydrazone imine A and diazenylenamine B forms, providing the carbon chemical shifts for the tautomers A and B of compounds 1a-g and 2a-e. The comparison of the carbon chemical shifts for the tautomer B of compounds 1d, 1f , and 2b in deuteriodimethyl sulfoxide with those in deuteriotrifluoroacetic acid showed that the C_4a, C₅, and diazenyl carbons were considerably shielded presumably due to the azo N-deuteration in deuteriotrifluoroacetic acid.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Chemical shifts of methyl substituted cis-decahydroquinolines

¹⁵N Chemical shifts of cis-decahydroquinoline, N-methyl-cis-decahydroquinoline, and of 19 methyl substituted NH- and NCH₃-cis-decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature ¹³C NMR spectroscopy.     

15N NMR studies of amino acids and their reaction products with formaldehyde

Natural abundance ¹⁵N NMR spectroscopy has been used to investigate the effect of pH on the ¹⁵N chemical shifts of lysine and of ε-hydroxymethyllysine. A computer calcualtion which fits the chemical shifts of both α-and ε-nitrogen atoms versus pH has been used to predict the pK_a values. ¹⁵N chemical shifts and some ¹J(¹⁵NH) values of some other amino acids and of their reaction products with formaldehyde are also reported.     

15N NMR spectral parameters of compounds of the N-methylpyrazole series

The¹⁵N NMR chemical shifts and¹⁵N-¹H SSCCs are presented for substituted N-methylpyrazoles with substituents such as CH₃, NO₂, Br, Cl, NH₂, O=CNH₂, O=CPh, and COOH at the carbon atoms. The¹⁵N chemical shifts of the cyclic atoms of nitrogen and the nitro groups are discussed as well as the geminal and vicinal SSCCs of the ring nitrogen atoms with the hydrogen atoms of the CH and CH₃ fragments.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117334 Moscow. D. I. Mendeleev Chemico-Technological Institute, Moscow, Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2554–2561, November, 1992.     

Aminodiphenylphosphanes: Isotope‐induced chemical shifts 1Δ14/15N(31P), coupling constants 1J(31P,15N), and chemical shifts δ15N and δ31P

A series of aminodiphenylphosphanes 1 [Ph₂P‐N(H)tBu ( a ), ‐NEt₂ ( b ), ‐NiPr₂ ( c )], 2 [Ph₂P‐NHPh ( a ), ‐NH‐2‐pyridine ( b ), ‐NH‐3‐pyridine ( c ), ‐NH‐4‐pyridine ( d ), NH‐pyrimidine ( e ), NH‐2,6‐Me₂‐C₆H₃ ( f ), NH‐3‐Me‐2‐pyridine ( g )], 3 [Ph₂P‐N(Me)Ph ( a ), ‐NPh₂ ( b )], and N‐pyrrolyldiphenylphosphane 4 (Ph₂P‐NC₄H₄) was prepared and studied by NMR (¹H, ¹³C, ³¹P, ¹⁵N NMR) spectroscopy. The isotope‐induced chemical shifts ¹Δ^14/15N(³¹P) were determined at natural abundance of ¹⁵N by using HEED INEPT experiments. A dependence of ¹Δ^14/15N(³¹P) on the substituents at nitrogen was found (alkyl < H < aryl; increasingly negative values). The magnitude and sign of the coupling constants ¹J(³¹P,¹⁵N) (positive sign) are dominated by the presence of the lone pair of electrons at the phosphorus atom. The X‐ray structural analysis of 2b is reported, showing the presence of dimers owing to intermolecular hydrogen bridges in the solid state. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:542–550, 2001     

A ‘shiftless’ relaxation reagent for metal nuclide and nitrogen-15 magnetic resonance in aqueous solution

Addition of small amounts of [Gd(2 : 2 : 1)]³⁺ cryptate to aqueous solutions containing ¹¹¹Cd²⁺ or formamide decreases metal nuclide or nitrogen-15 spin-lattice (T₁) relaxation times without affecting cadmium or nitrogen chemical shifts. This cryptate is thereby demonstrated to have substantial promise for greatly decreasing the time necessary to obtain natural abundance metal nuclide or ¹⁵N NMR spectra with satisfactory signal-to-noise ratios for many compounds with long metal or ¹⁵N relaxation times.     

Oligomeric complexes of some heteroaromatic ligands and aromatic diamines with rhodium and molybdenum tetracarboxylates: 13C and 15N CPMAS NMR and density functional theory studies

Seven new oligomeric complexes of 4,4′‐bipyridine; 3,3′‐bipyridine; benzene‐1,4‐diamine; benzene‐1,3‐diamine; benzene‐1,2‐diamine; and benzidine with rhodium tetraacetate, as well as 4,4′‐bipyridine with molybdenum tetraacetate, have been obtained and investigated by elemental analysis and solid‐state nuclear magnetic resonance spectroscopy, ¹³C and ¹⁵N CPMAS NMR. The known complexes of pyrazine with rhodium tetrabenzoate, benzoquinone with rhodium tetrapivalate, 4,4′‐bipyridine with molybdenum tetrakistrifluoroacetate and the 1 : 1 complex of 2,2′‐bipyridine with rhodium tetraacetate exhibiting axial–equatorial ligation mode have been obtained as well for comparison purposes. Elemental analysis revealed 1 : 1 complex stoichiometry of all complexes. The ¹⁵N CPMAS NMR spectra of all new complexes consist of one narrow signal, indicating regular uniform structures. Benzidine forms a heterogeneous material, probably containing linear oligomers and products of further reactions. The complexes were characterized by the parameter complexation shift Δδ (Δδ = δ_complex ? δ_ligand). This parameter ranged from around ?40 to ?90 ppm in the case of heteroaromatic ligands, from around ?12 to ?22 ppm for diamines and from ?16 to ?31 ppm for the complexes of molybdenum tetracarboxylates with 4,4′‐bipyridine. The experimental results have been supported by a density functional theory computation of ¹⁵N NMR chemical shifts and complexation shifts at the non‐relativistic Becke, three‐parameter, Perdew‐Wang 91/[6‐311++G(2d,p), Stuttgart] and GGA–PBE/QZ4P levels of theory and at the relativistic scalar and spin‐orbit zeroth order regular approximation/GGA–PBE/QZ4P level of theory. Nucleus‐independent chemical shifts have been calculated for the selected compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

15N nuclear magnetic resonance spectroscopy. Natural abundance 15N NMR of monosubstituted indoles

¹⁵N chemical shifts of twenty-four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2-, 3- and 5-ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl₃. ¹³C NMR data for previously unreported compounds are also reported.     

Dynamic 15N NMR studies of iron phosphine complexes containing coordinated dinitrogen

The ¹⁵N‐labelled iron dinitrogen complexes trans‐[FeH(N₂)(PP)₂]⁺[BPh₄]^? (PP = dppe, depe, dmpe) and cis‐[FeH(N₂)(PP₃)]⁺[BPh₄]^? were prepared in situ by exchange of unlabelled coordinated dinitrogen with ¹⁵N₂. ¹⁵N NMR chemical shifts and coupling constants are reported. The ¹⁵N spectra exhibit separate signals for the metal‐bound and terminal nitrogen atoms of the coordinated N₂. The ¹⁵N resonances display ¹⁵N, ¹⁵N coupling as well as ³¹P, ¹⁵N coupling and long‐range ¹⁵N, ¹H coupling when there is a metal‐bound hydrido ligand. Exchange between free and coordinated dinitrogen was monitored by magnetization transfer between ¹⁵N‐labelled sites using an inversion–transfer–recovery experiment. Exchange between the metal‐bound and terminal nitrogen atoms of coordinated N₂ was also monitored by magnetization transfer and this could proceed by N₂ dissociation or by an intramolecular process. Copyright © 2003 John Wiley & Sons, Ltd.     

NMR-spektroskopische Untersuchungen an Mercaptophosphazenen. II. NMR-spektroskopische Untersuchungen an 15N-markierten Mercaptophosphazenen

N.M.R. Spectroscopic Investigations of Thiophosphazenes. II. N.M.R. Spectroscopic Investigations of ¹⁵N Labelled Thiophosphazenes Completely ¹⁵N labelled compounds of the type ¹⁵N₃P₃Cl_6?n(SR)_n, R = Et or Ph; n = 0, 2, 4, or 6, and of the type ¹⁵N₄P₄Cl_8?n(SR)_n, R = Et; n = 0, 4, or 8, were prepared and investigated by means of both ³¹P n.m.r. spectroscopy and ¹⁵N n.m.r. spectroscopy respectively. The coupling constants ²J_PP, in some cases only found by simulating the spectra, and the coupling constants ¹J_PN are given. The values of these coupling constants and their relation are discussed. The general tendency is visible, that with increasing coupling constant ¹J_PN the coupling constant ²J_PP decreases. With increasing grade of substitution n the ¹⁵N chemical shifts are changed to higher fields.     

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

All carbon-13 chemical shifts for 11 para-substituted N,N-dimethylbenzamides in 1 mole % chloroform solution are reported, with assignments based upon double resonance experiments, analogy to chemical shifts of benzamide, and self-consistency between experimental and calculated values using recognized substituent parameters. In contrast to earlier reports, the aryl carbon chemical shift assignments for N,N-dimethylbenzamide are C-2, 127.0; C-3, 128.7; C-4, 129.4, and for p-chloro-N,N-dimethylbenzamide are C-1, 134.6; C-4, 135.5 ppm, relative to internal TMS. Good Hammett correlations (σ_p) are reported for ¹³C chemical shifts of C-1 (σ = 11.9 ppm) and even for the carbonyl group (σ = ?2.3 ppm) but are markedly improved if correlated with σ_p+ (σ = 9.5 ppm) and Dewar's F (σ = ?1.9 ppm), respectively. Excellent Swain–Lupton F and R correlations were found for some of the ¹³C chemical shifts and yielded values for percent resonance contributions to transmission of substituent effects as follows, C-1, 75 ± 4%; C-2, 51 ± 3%; C?O, 31±2%. These are compared to similar values calculated from the C?O of benzoic acids of 34±10%, and from the nitrogen-15 chemical shifts of benzamides of 56±2%. Correlations of these ¹³C δ values and ¹⁵N δ values with rotation barriers (ΔG) for N,N-dimethylbenzamides were examined, and it was found that while C?O δ values correlated only poorly the C-1 δ values correlated very well, but the best correlation was for ¹⁵N δ values of benzamides. It is suggested that Δ G and δ ¹⁵N are intrinsically related due to their numerical correlation, and the close similarity in percent resonance contribution of substituent influence on these parameters.     

15N nuclear magnetic resonance spectroscopy. Natural-abundance 15N spectra of aliphatic oximes

¹⁵N chemical shifts of the Z and E isomers of twenty-two ketoximes and fourteen aldoximes have been determined at the natural-abundance level of ¹⁵N, using Fourier transform methods. The influences of π delocalization, methyl substituents and solute concentration on the oxime nitrogen shielding have been determined. The ¹⁵N shifts for oximes of several cycloalkanones have been measured and the influence of ring size on the chemical shifts is discussed.     

Computational NMR Spectroscopy of Transition‐Metal/Nitroimidazole Complexes: Theoretical Investigation of Potential Radiosensitizers

The computed chemical shifts of transition‐metal complexes with dimetridazole (= 1,2‐dimethyl‐5‐nitro‐1H‐imidazole; 1 ), a prototypical nitro‐imidazole‐based radiosensitizer, are reported at the GIAO‐BP86 and ‐B3LYP levels for BP86/ECP1‐optimized geometries. These complexes comprise [MCl₂( 1 )₂] (M = Zn, Pd, Pt), [RuCl₂(DMSO)₂( 1 )₂], and [Rh₂(O₂CMe)₄( 1 )₂]. Available δ(¹H) and δ(¹⁵N) values, and Δδ(¹H) and Δδ(¹⁵N) coordination shifts are well‐reproduced theoretically, provided solvation and relativistic effects are taken into account by means of a polarizable continuum model and suitable methods including spin–orbit (SO) coupling, respectively. These effects are particularly important for the metal‐coordinated N‐atom, where the contributions from solvation and relativity can affect δ(¹⁵N) and Δδ(¹⁵N) values up to 10–20 ppm. The ¹⁹⁵Pt chemical shifts of cis‐ and trans‐[PtCl₂( 1 )₂] are well‐reproduced using the zero‐order regular approximation including SO coupling (ZORA‐SO). Predictions are reported for ⁹⁹Ru and ¹⁰³Rh chemical shifts, which suggest that these metal centers could be used as additional, sensitive NMR probes in their complexes with nitro‐imidazoles.     

Regioselectively [15NO2]-labeled N-methoxypicramide and DPPH prepared by using crown ether and solid sodium [15N]nitrite

The present paper reports the regioselective [¹⁵NO₂]-labeling of N-methoxy-2,4,6-trinitroaniline and 2,2-diphenyl-1-picrylhydrazine (reduced DPPH). Starting from N-methoxy-2,6-dinitroaniline, or N-methoxy-2,4-dinitroaniline, nitration in methylene chloride with solid sodium [¹⁵N]nitrite and 15-crown-5-ether afforded N-methoxy-2,6-dinitro-4-[¹⁵N]nitroaniline and N-methoxy-2,4-dinitro-6[¹⁵N]nitroaniline, respectively. The same compounds could be prepared in higher purity by nitrodecarboxylation (ipso-substitution) under the same conditions starting from N-methoxy-4-carboxy-2,6-dinitroaniline (4-methoxyamino-3,5-dinitrobenzoic acid) and N-methoxy-2-carboxy-4,6-dinitroaniline (2-methoxyamino-3,5-dinitrobenzoic acid). Similarly,ipso-substitution of 2,2-diphenyl-1-(4-carboxy-2,6-dinitrophenyl)-hydrazine afforded, under the same reaction conditions, 2,2-diphenyl-1-(2,6-dinitro-4-[¹⁵N]nitrophenyl)-hydrazine. By¹H-NMR and¹³C-NMR it was also observed that under these reaction conditions a¹⁴NO₂ group can be replaced by a¹⁵NO₂ group.