13C-15N spin-spin coupling constants of amides: H-bonding effects in a cyclohexapeptide

The effect of intramolecular H-bonding and solvent acidity on the magnitude of one-bond ¹³C-¹⁵N spin-spin coupling constants has been examined using specifically ¹⁵N-labeled $\text{cyclo}$-(Gly-L-Pro-Gly)₂ and related linear peptides.     

NMR spectra of silatranes and M ← N (M = C, Si, Ge, Sn, Pb) bond lengths in atranes: Substituent effects

The literature data on X substituent influence on the ¹H, ²⁹Si and ¹⁵N NMR chemical shifts (δ) and coupling constants (J) of Si-substituted silatranes , as well as M-N bond lengths (d) in atranes (M = C, Si, Ge, Sn, Pb) have been analyzed. It was established for the first time that the δ, J and d values depend not only on the inductive and resonance effects but also on the polarizability of X substituents. The polarizability contribution ranges from 8% to 25%.     

Spin-spin coupling constants 13C-15N and 1H-15N in the investigation of azido-tetrazole tautomerism in a series of 2-azidopyrimidines

A new method was developed for the investigation of an azido-tetrazole equilibrium based on using a complex analysis of ¹³C-¹⁵N and ¹H-¹⁵N spin-spin coupling constants. The use of this approach became possible due to the selective inclusion of ¹⁵N isotopes into the structures of 2-azidopyrimidines and their cyclic analogs tetrazolo[1,5-a]pyrimidines.     

Stereochemistry and configurational stability of cyclic NH- and N-dimethylcarbamoyldialkoxyamines

On the basis of the data from the ¹H, ¹³C, and ¹⁵N NMR spectra it was established that perhydro-1,3,2-dioxazine has the chair conformation with the equatorial orientation of the NH proton; the barrier to inversion at the N atom is G=21.9 kcal/mole. The preferred conformer of its 4-methyl derivative has the 2e,4e configuration. Stereospecific spin-spin coupling constants ⁴J_e-HCONH-e, ³J¹³CONH-e, and ³J¹⁵NOCH-e were obtained for these compounds. 1,3,2-Dioxazolidine has a bent envelope conformation with the axial orientation of the NH proton; a stereospecific spin-spin coupling constant ⁴J_e-HCONH-e was obtained, and the invariability of the PMR spectrum at 170C was demonstrated.Communication 58 of the Series Asymmetric Nitrogen, for Communication 57 see [1]; Communication 35 of the Series Geminal Systems, for Communication 34, see [2].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 24, No. 3, pp. 396–402, March, 1988.     

NMR-spektroskopische Untersuchungen an 15N-markierten N-Phosphorylphosphazenen und Imidodiphosphorsäure-Derivaten

N.M.R. Spectroscopic Studies of ¹⁵N Labelled N-Phosphorylphosphazenes and Imidodiphosphoric Acid Derivatives ¹⁵N labelled compounds were prepared and investigated by means of ³¹P- and ¹⁵N-NMR spectroscopy. The chemical shift values δ_P and δ_N, and the coupling constants ¹J_PN and ²J_PP are discussed and interpreted qualitatively by semiempirical quantumchemical calculations (CNDO/2) using POPLE 'S ΔE-model.     

Specific C-H...N intramolecular interaction in 1-vinyl-2-cyanoethylthiobenzimidazole with the formation of a nine-membered intramolecular ring,according to1H and13C NMR data

In the¹H NMR spectrum of 1-vinyl-2-cyanoethylthiobenzimidazole, an abnormal downfield shift has been found in the signal of the -hydrogen atom of the vinyl group, and also an increase in the corresponding direct¹³C-¹H spin-spin coupling constant, in comparison with other 2-substituted benzimidazoles. This indicates a specific C-H...N intramolecular interaction in this molecule between the -hydrogen atom and the cyano nitrogen atom, forming a nine-membered intramolecular ring.Translated from Translated from Izvestiya Akademii Nauk SSSR No. 10, pp. 2285–2288, October, 1991.     

Nitropyrazoles

The structures of substitutedN-aminonitropyrazoles and 1- and 2-amino-4-nitro-1,2,3-triazoles as well as the site of protonation of 1-aminopyrazole were determined based on the¹H,¹³C, and¹⁵N (¹⁴N) NMR spectra. The¹³C NMR spectra were recorded under conditions of¹³C-{¹H,¹⁴N} triple resonance. Effects of substituents in the pyrazole ring on the¹³C and¹⁴N chemical shifts were studied. The¹³C,¹H and¹⁵N,¹H spin-spin coupling constants, obtained using techniques of [¹H]¹³C and [¹H]¹⁵N polarization transfer (SPT, INEPT), were measured, fully assigned, and discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2181–2186, November, 1995.For Part 8, see Ref. 1.     

Atranes

The kinetics of the hydrolysis of 15 1-alkyl-, 1-alkoxy- and 1-hydrosilatranes in an aqueous medium has been studied. The hydrolysis reaction is described by a first-order kinetic equation. 1-Hydrosilatrane is hydrolyzed most readily and 1-isopropyl- and 1-tert-butoxysilatranes with the greatest difficulty. A correlation has been drawn up of the logarithms of the rate constants of the hydrolysis of the silatranes and the ^* constants of the substituents, the influence of the latter on the reaction has been discussed, and a scheme for its mechanism has been put forward.For part XVII, see [1].     

Azines and azoles: CXXVII. 5-phenyl-7<Emphasis Type="Italic">H</Emphasis>-[1,2,4]triazolo[5,1-<Emphasis Type="Italic">b</Emphasis>][1,3]thiazin-7-ones: Synthesis and structure

Reactions of 1-acylthiosemicarbazides with methyl 3-phenylprop-2-ynoate provide a new one-step procedure for the synthesis of 2-substituted 5-phenyl-7H-[1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones. The product structure was determined on the basis of scalar spin-spin coupling constants ² J(¹H-¹⁵N) and ³ J(¹H-¹⁵N) in the ¹H and ¹⁵N NMR spectra and was proved by X-ray analysis. Methyl 3-phenylprop-2-ynoate reacted with 1-acetylthiosemicarbazide in ethanol in the presence of H₂SO₄ to give 3-methyl-7-phenyl[1,2,4]triazolo[3,4-b]-[1,3]thiazin-5-one as the only product.     

Study of specific C-H...N intramolecular interactions in heteroaryl vinyl ethers,on the basis of factor analysis of1H and13C NMR spectral parameters

On the basis of a factor analysis of the¹H and¹³C NMR spectral parameters of the vinyloxy group in a broad series of aryl and heteroaryl vinyl ethers, it has been established that these parameters change mainly under the influence of the electronic effect of the aromatic fragment and specific C-H...N intramolecular interaction of the -hydrogen atoms of the vinyl group with an endocyclic nitrogen atom. It has been shown that the parameters most sensitive to the specific C-H...N. interaction are the chemical shifts of the -proton and -carbon of the vinyl group, and also the spin-spin coupling constant between these atoms.Translated from Izvestiya Akademii Nauk SSSR, No. 10, pp. 2289–2297, October, 1991.     

Investigation of N-nitrohydrazines by the NMR method

Functionally substituted N-nitrohydrazines were studied by heteronuclear NMR. It was shown that all the investigated products from nitration of the trimethylsilyl derivatives of functionally substituted hydrazines contain the N-NO₂ fragment. The chemical shift of the nitrogen atoms of the hydrazine fragment in the¹⁵N NMR spectra and the spin-spin coupling constants were used as the main tests for structural identification. It was established that the number of recordable conformers decreases in the transition from the trimethylsilyl phenylhydrazine derivatives to the nitrohydrazines as a result of the conformational flexibility of the N(NO₂)CO fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2024–2031, September, 1991.     

Application of 13C and 15N spectroscopy to the study of electronic delocalization in N?N bonds: Nitrosamines,hydrazones, triazenes and related protonated species

¹³C and ¹⁵N spectroscopies at natural abundance have been applied to the study of nitrogen lone-pair delocalization in N? N containing compounds: nitrosamines, nitramines, hydrazines, hydrazones and triazenes. Structure-chemical shift correlations have been derived for nitrosamines; the ¹³C upfield effect of a γ substituent has been used for assigning the configuration of both diastereoisomers in N,N-unsymmetrically substituted nitrosamines. Equations have been computed which permit the prediction of the electronic delocalization, expressed in terms of free enthalpy of activation ΔG, as a function of δ¹⁵N and of the length of the N? N bond. ¹⁵N spectroscopy has also been applied to the study of the protonated species of nitrosamines and of acceptor-donor complexes of nitrosamines with Lewis acids. The behaviour of such N? N containing compounds is compared to that of amides.     

Determination of hydrogen depth profiles in polymer films by the 15N nuclear reaction technique

Summary It has been shown that the ¹⁵N nuclear reaction technique for hydrogen profiling can be used for the characterization of polymer films. With an optimized sample geometry, a depth resolution of 5 nm near the sample surface is achieved. A special -ray detector allows radiation damage in the sample to be minimized. Since the ¹⁵N technique discriminates between the hydrogen isotopes H and D, a suitable contrast between the different components of a polymer film is achieved by deuterating one component of the polymer. This has been utilized in the study of the surface-induced lamellar ordering within diblock copolymer films.     

13C, 15N and 29Si NMR spectra of triazasilatranes

¹³C, ¹⁵N and ²⁹Si chemical shifts and ²⁹Si¹H, ²⁹Si¹³C and ²⁹Si¹⁵N coupling constants as well as SiH bond stretching frequencies in the triazasilatranes (I) (2,5,8,9-tetraaza-1-silatricyclo[3.3.3.0^1,5] undecanes) and model compounds, tris(alkylamino)silanes with R_Si = H, Me, CH₂CH (Vi) and C₆H₅ (Ph) were measured. A stronger intramolecular N → Si bonding was revealed in I compared with their oxygen analogues, silatranes (II). This was assumed to be caused by the higher polarity of the equatorial SiX bonds in I (X = NH) in comparison with II (X = O).     

Utilization of deuterium and15N as activable tracers in solid state sciences

The sensitivity in the determination of deuterium and¹⁵N by nuclear reactions was examined for the following reactions: (1)¹⁵N(d,n)¹⁶O (or p+)+(6.13, 7.11 MeV); (2) D(³He,)⁴He (13 MeV); and (3)¹⁵N(,n)¹⁸F. By these activations with suitable etching techniques, sub ppm regions of D and¹⁵N have proved to be measurable with their depth profiles. Some fundamental properties of hydrogen and nitrogen in silicon are under investigation using of these activable tracers.     

15N and17O NMR spectra of vinyl ethers of pyridine and quinoline

Conclusions ¹⁵N (¹⁴N) and¹⁷O NMR spectra have been obtained on vinyl ethers of pyridine and quinoline, with unenriched samples. The principal factor determining the chemical shifts is p- conjugation of the unshared pairs of the heteroatom with the unsaturated fragments of the molecule; an additional contribution in the case of the¹⁵N signals comes from interaction of the nitrogen atom with a proton through space.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 769–773, April, 1987.     

15N-Azides as practical and effective tags for developing long-lived hyperpolarized agents

Azide moieties, unique linear species containing three nitrogen atoms, represent an attractive class of molecular tag for hyperpolarized magnetic resonance imaging (HP-MRI). Here we demonstrate (¹⁵N)₃-azide-containing molecules exhibit long-lasting hyperpolarization lifetimes up to 9.8 min at 1 T with remarkably high polarization levels up to 11.6% in water, thus establishing (¹⁵N)₃-azide as a powerful spin storage for hyperpolarization. A single (¹⁵N)-labeled azide has also been examined as an effective alternative tag with long-lived hyperpolarization. A variety of biologically important molecules are studied in this work, including choline, glucose, amino acid, and drug derivatives, demonstrating great potential of ¹⁵N-labeled azides as universal hyperpolarized tags for nuclear magnetic resonance imaging applications.

This work demonstrates that ¹⁵N-labeled azides are practical and effective tags for developing long-lived hyperpolarized MRI agents and can offer hyperpolarization lifetimes up to 9.8 min at 1 T and high polarization levels up to 11.6% in water.     

Amines α et β acétyléniques. Couplages J(15N?H), J(15N?13C) et hybridation de l'azote

¹H and ¹³C NMR spectra of ¹⁵N-methylaniline, ¹⁵N-methylphenylpropargylamine and ¹⁵N-methylphenylpropynylamine have been studied. The s character of nitrogen, deduced from ¹J(¹⁵N? ¹³C) and ¹J(¹⁵N? ¹³C), indicates that nitrogen hybridisation is intermediate between sp³ and sp² in ¹⁵N-methylaniline and ¹⁵N-methylphenylpropargylamine, while nitrogen is sp² in the α-acetylenic amine. The ¹J(¹⁵N? ¹³C_sp)cou pling constant calculated with the help of Binsch's relation does not agree with the experimental value, suggesting that orbital and dipolar mechanisms make substantial contributions to this coupling constant.