Natural abundance 17O NMR spectroscopy of heteroaromatic Nitro compounds

The ¹⁷O chemical shift data, at natural abundance, for selected nitroquinolines, nitroindoles, nitroindazoles and nitrothiophenes are reported. In the absence of a peri or a lone-pair repulsion effect, the nitroquinolines' chemical shifts differ little from those of their carbocyclic analogs. However, the signal for 5-nitroquinoline, 2 , is deshielded by 25 ppm compared to 6-nitroquinoline, 1 , and the ¹⁷O nucleus in 8-nitroquinoline, 3 , is deshielded by 49 ppm compared to that in 1 . Both these shifts are attributed to rotation of the nitro group from the plane of the heteroaromatic ring arising from peri hydrogen interaction and lone pair repulsion, respectively. The signals for nitro groups on electron excessive ring systems (e.g., indoles and thiophenes) are shielded relative to corresponding ones in electron deficient heterocyclic ring system analogs. The chemical shifts for the π-excessive systems are interpreted in terms of electronic effects.     

A 17O NMR study. On the correlation of ionization potentials and 17O chemical shifts in 4-substituted pyridine-N-oxides and 4-substituted N-(benzylidene)phenylamine-N-oxides

The approximate linear correlation between first ionization potentials and ¹⁷O chemical shifts for 4-substituted pyridine-N-oxides and 4-substituted N-(benzylidene)phenylamine-N-oxides is presented. The obtained results are used to estimate the ¹⁷O chemical shift in 4-N,N-dimethyl pyridine-N-oxide. The obtained results are discussed in relation to similar correlations in substituted benzenes and pyridines. The linear correlation between oxygen atomic net charge and ¹⁷O chemical shift for 4-substituted pyridine-N-oxides and 4-substituted N-(benzylidene)phenylamine-N-oxides is also presented.     

Natural abundance 17O NMR spectra of carbonyl metal clusters of the iron triad

¹⁷O NMR spectra (in natural abundance) have been recorded, at room temperature, for a variety of polynuclear iron, ruthenium and osmium carbonyl clusters. Rather sharp linewidths have been observed for stereochemically rigid species, whereas linewidths as large as about 200 Hz have been obtained for fluxional molecules. Even though the observed chemical shift range for terminal CO groups is not very large (about 50 ppm), taking into account linewidths, metal triad and substituent effects have been observed to different extents.     

Natural abundance 17O NMR spectroscopy of heterocyclic N-oxides and Di N-oxides. Structural effects

The ¹⁷O chemical shift data for a series of azine N-oxides, diazine N-oxides and di-N-oxides at natural abundance are reported. Isomeric methyl substituted quinoline N-oxides exhibited chemical shifts which are interpreted in terms of electronic and compressional effects. The ¹⁷O chemical shift for 8-methylquinoline N-oxide (370 ppm) is deshielded by 25 ppm more than predicted, based upon electronic considerations. The ¹⁷O chemical shift for the N-oxide of 8-hydroxyquinoline (289 ppm) is substantially shielded as a result of intramolecular hydrogen bonding. The relative ¹⁷O chemical shifts for diazine N-oxides of pyrazine, pyridazine and pyrimidine follow predictions based on back donation considerations. Because of solubility limitations, spectra of only two N,N′-dioxides were obtained. The chemical shift of benzopyrazine di N-oxide in acetonitrile was shielded by 18 ppm compared to that of its mono N-oxide.     

17O NMR study of isomeric 2-R-2-oxo-1,3,2-dioxaphosphorinanes

Oxygen-17 NMR spectra were obtained from the four pairs of isomeric 2-R-2-oxo-1,3,2-dioxaphosphorinanes, where R=OMe (2), NMe₂ (3), H (4) or Me (5). The isomerism has been previously shown to be configurational at phosphorus, with one isomer of each pair having an equatorial phosphoryl oxygen (a isomer), and the other an axial orientation for phosphoryl oxygen (b isomer). Only data for the phosphoryl oxygen are reported. Substitution of OMe or NMe₂ for H or Me produced upfield shifts of 27.9-41.8 ppm. In all cases, the chemical shifts of the a isomers were upfield of the b analogs, with differences of 7.9, 18.0, 20.3 and 8.6 ppm for 2—5, respectively. The absolute values of ¹J(³¹P¹⁷O) were 5–9 Hz larger for the a isomers.     

Condensation of 2-aminobenzimidazoles with o-substituted benzoyl chlorides

Translated from Khimiya Geterotsiklicheksikh Soedinenii, No. 2, pp. 272–273, February, 1989.     

An unusual reaction of 2-(2-pyridylcarbonyl)- and 2-(2-quinolylcarbonyl)benzoyl chlorides with p-nitroaniline

In the reaction of 2-(2-pyridylcarbonyl)benzoyl chloride, which exists in the form of 6,11-dioxo-6,11dihydrobenzo[b]quinolizinium chloride, with p-nitroaniline, 2-(4-nitrophenylimino)-6, 11-dihydro-2H-benzo-[b]quinolizine-6, I I -dione is unexpectedly formed. When it reacts with water or methanol there is an opening of the quinolizine ring and aromatization of the quinoid fragment with the formation of 2-[4-(4nitrophenylamino)-2-pyridylcarbonyl]benzoic acid or its methyl ester. Under the action of antimony pentachloride, 2- 2-quinolylcarbonyl)benzoylchloride-3 (2-quinolyl)-3-chloro- 1, 3-dihydrobenzo[c]furan-1 -one -is converted to 3-(2-quinolyl)-1,3-dihydrobenzo[c]furan-1-on-3-ylium hexachlorantimonate, which undergoes isomerizing recyclization upon heating to 7,12-dioxo-7,12-dihydrobenzo[b/ hexachloroantimonate. The latter enters into an analogous reaction with p-nitroaniline, thereby forming 5-(4-nitrophenylimino)-7,12-dihydro-5H-dibenzo[b,f]quinolizine-7,2-dione.Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 938–944, July, 1995. Original article submitted May 31, 1995.     

Synthesis and 15N- and 17O-NMR Spectra of 5-Methyl(15N2)[O2,O4-17O2]uridine (= (15N2)[O2,O4-17O2]Ribosylthymine)

The 5-methyl(¹⁵N₂)[O²,O⁴-¹⁷O₂]uridine (= (¹⁵N₂)[O²,O⁴-¹⁷O ₂]ribosylthymine; 15 ) was synthesized and analyzed by ¹⁵N- and ¹⁷O-NMR spectroscopy. (¹⁵N₂)Urea was condensed with 2,3-dibromo-2-methylpropanoyl chloride ( 3 ) and cyclized to form (¹⁵N₂)thymine ( 5 ). After glycosidation, the ¹⁷O isotopes were introduced in two separate steps: hydrolytic ring opening of 2,5′-anhydro derivative 9 and hydrolysis of 3-nitro-1H-1,2,4-triazole derivative 12 with labelled water in the presence of a strong base. The ¹⁵N- and ¹⁷O-NMR spectra (Fig.) of 15 in phosphate-buffered water serve as references for heteronuclear NMR spectra of labelled RNA fragments.     

Ab initio MO calculations and 17O NMR at natural abundance of para-substituted acetophenones

¹⁷O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para-substituted acetophenones, X? C₄H₆? COCH₃, where X = NH₂, OCH₃, F, Cl, CH₃, H, COCH₃, CN, NO₂. The ¹⁷O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σ_I and σ_R⁺ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρ_I and ρ_R indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π-electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λ values are also reported, and the role of the average excitation energy, ΔE, in determining ¹⁷O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ-electron density is the dominant feature controlling ¹⁷O SCS values.     

High-resolution 17O NMR spectroscopy of wadsleyite (beta-Mg2SiO4)

The sensitivity of high-resolution 17O (I = 5/2) NMR spectroscopy of solids has advanced significantly in recent years. Here, we show that excellent results are now obtainable from milligram quantities of 17O-enriched materials, thereby allowing the technique to be applied to silicate phases synthesized under very high pressures in a multiple-anvil apparatus. We report the first 17O NMR study of beta-Mg2SiO4 (9.6 mg of 35% 17O-enriched material, synthesized at p = 16 GPa and T = 1873 K), a dense phase believed to have a significant role in the Earth's mantle. Using STMAS at magnetic fields of B0 = 9.4 and 11.7 T and MQMAS at B0 = 18.8 T, we have resolved and assigned all four crystallographically distinct O sites and determined their chemical shift and quadrupolar parameters.     

2- and 4-substituted 5-fluoropyrimidines

2- and 4-substituted 5-fluoropyrimidines were synthesized by the reaction of 2,4-dichloro-5-fluoropyrimidine with alkoxides, phenols, and aromatic and heterocyclic amines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 117–119, January, 1973.     

Carbon-13 NMR spectra of some 4- and 5-substituted pyrimidines

Carbon-13 NMR chemical shifts and carbon-proton coupling constants for nine 4-substituted and six 5-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Carbon-proton coupling constants fail to correlate with substituent electronegativity.     

NMR study of molecular complexes of 1-, 2- and 3-substituted indole donors with polynitroaromatic acceptors2

The stability of electron donor-acceptor complexes formed, in CDCl₃ solutions, between differently-substituted indoles (1-, 2- and 3-Me, Et, i.Pr, t.Bu, OMe, SMe, COOEt) and 1,3,5-trinitrobenzene, 1,3-dinitroben-zene and their derivatives was investigated by NMR of the acceptor's protons. From magnetically non-equivalent protons of the acceptor, different association constants K for one complex formation could be measured in many cases, but only aromatic protons led to reliable' K values.     

Synthesis of (15N2)[17O]Urea, (15N2)[O2, O4-17O2]Uridine,and (15N3)[O2-17O]Cytidine

A general synthetic approach for the synthesis of ¹⁵N- and ¹⁷O-doubly labelled pyrimidine nucleosides is described. The ¹⁵N isotopes in uridine and the ¹⁷O isotope in the urea-derived carbonyl group of uridine and cytidine originate from (¹⁵N₂)[¹⁷O]urea ( 5 ) which was synthesized from ¹⁵NH₄Cl, thiophosgene ( 1 ), and H₂[¹⁷O]. The third ¹⁵N isotope of cytidine in 4-position stems from the substitution of the 1,2,4-triazole moiety of (¹⁵N₂)[O²-¹⁷O]uridine derivative 8a/b with ¹⁵NH₄OH. Hydrolysis of the same key intermediate 8a/b with Na[¹⁷O]H/H₂[¹⁷O] introduced the second ¹⁷O isotope into the 4-position of uridine. The ¹⁵N- and ¹⁷O-NMR spectra of the target compounds 12 and 14 in phosphate-buffered H₂O serve as references for heteronuclear NMR spectra of labelled RNA fragments.     

Calculating the Thermodynamics of Weakly Hydrogen-Bonded Complexes from Heteronuclear NMR Data: Base-pairing stabilities of a 5-methyl(15N2)[O2, O4-17O2]uridine (= (15N2)[O2,O4-17O2]ribosylthymine) derivative,and structural implications

2′,3′-O-Isopropylidene-5-methyl(¹⁵N₂)[O²,O⁴-¹⁷O₂]uridine (= 2′,3′-O-isopropylidene (¹⁵N₂)[O²,O⁴-¹⁷O₂]-ribosylthymine; 1 ) was analyzed by ¹⁵N-and ¹⁷O-NMR spectroscopy. The ¹⁵N and ¹⁷O chemical shifts revealed, in the absence and presence of unlabelled 2′,3′-O-isopropylideneadenosine ( 2 ), the formation of thymine-thymine and thymine-adenine base pairs in CHCl₃. As expected, cyclic complexes stabilized by two H-bonds occurred at low temperatures, but at elevated temperatures, the data suggest that open complexes involving only one H-bond prevailed. The ¹⁷O-NMR data showed the cyclic thymine-adenine pair in a reverse base pair geometry. The open base pair involved contacts to the urea-derived carbonyl O-atom of thymine. The thermodynamics of complex formation of the cyclic and open forms in both homo and hetero pairs were calculated from the temperature and concentration dependence of the ¹⁵N-NMR data using a new method. It involves a fitting procedure onto the experimental isotherms using a theoretically derived function with the standard Gibbs free energy as a parameter to be optimized. ΔH° and ΔS° were derived from a linear regression of ΔG°(T) vs. T. The fitting procedure circumvents the baseline problem and could be automated and used to calculate correct thermodynamics from UV-monitored melting curves of oligonucleotides. Since titrations are not involved, this dilution method should also be a useful alternative for stability studies of supramolecular complexes in H₂O and in organic solvents.     

17O NMR and computational study of a tetrasiliconiobate ion, [H(2+x)Si4Nb16O56](14-x)-

Rates of oxygen-isotope exchange were measured in the tetrasiliconiobate ion [H(2+x)Si(4)Nb(16)O(56)]((14-x)-) to better understand how large oxide ions interact with water. The molecule has 19 nonequivalent oxygen sites and is sufficiently complex to evaluate hypotheses derived from our previous work on smaller clusters. We want to examine the extent to which individual oxygen atoms react independently with particular attention given to the order of protonation of the various oxygen sites as the pH decreases from 13 to 6. As in our previous work, we find that the set of oxygen sites reacts at rates that vary over approximately 10(4) across the molecule at 6相似文献   

A 17O NMR study of the protonation of urea

¹⁷O NMR has been applied to the study of urea over a wide pH range, in fluorosulfonic acid and in magic acid (HFSO₃SbF₅). A 96 ppm diamagnetic chemical shift was observed on modifying the medium from an aqueous solution at pH 3 to a fluorosulfonic acid solvent. We attributed this shift to a protonation reaction at the urea oxygen having a pK_a of 0.1. A 36 ppm paramagnetic shift was observed in magic acid relative to the resonance position in fluorosulfonic acid, which is consistent with the formation of a diprotonated form of urea. Values of transverse and longitudinal relaxation rates were found to be equal as a function of pH and to double on lowering the pH from 2 to ?1.     

Proton-coupled 13C NMR spectra of 2- and 3-substituted pyridines

The proton-coupled ¹³C NMR and PMR spectra of pyridine and the 2- and 3-monosubstituted pyridines NC₅H₄X [where X=CH₃, CN, COCH₃, COOCH₃, N(CH₃)₂, NO₂, OCH₃, Cl, or Br] for one-molar solutions of the compounds in DMSO-D₆, have been analyzed. The signs and values of the ¹³C-¹H HSSCs have been determined. Equations have been obtained connecting the ¹³C-¹H SSCCs in the 2- and 3-substituted pyridines and the monosubstituted benzenes. A satisfactory correlation of ¹JCH with the F and R constants of the substituents has been shown.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1223–1230, September, 1984.     

NMR study on the structure and stability of 4-substituted aromatic iodosyl compounds

Two 4-substituted aromatic iodosyl compounds were investigated with regard to their solubility, stability and chromatographic behaviour. 1-Iodosyl-4-methoxy- and 1-iodosyl-4-nitro-benzene are soluble in methanol and provide acceptable 1H and 13C NMR spectra; however, gradual oxidation of the solvent was observed. LC-MS analyses suggest that unlike the parent substance, iodosylbenzene, which has a polymeric structure, both compounds rather exist in the monomeric form.