bluuebunny/crossref_metadata_2025 huggingface dataset:
15N NMR: Iminothiol‐thioamide tautomerism of 2‐mercaptobenzazoles and 1‐methyl‐2‐mercaptoimidazole
Authors: Balestrero R. S. , Forkey D. M. , Russell J. G.
Published: May 2005

15N NMR spectra of a number of 2‐mercaptoazoles were obtained and the position of the iminothiol‐thioamide prototropic tautomeric equilibrium was determined. Because of the large chemical shift difference of ca 100 ppm between the iminothiol and thioamide nitrogen atoms, the 15N chemical shifts of the S‐methyl and N‐methyl analogs of each tautomer provided reasonable chemical shift models for the same nitrogen atom in the tautomers. Only a small correction for an N‐methyl effect was required.
Variable‐temperature and‐concentration 1H and 7Li NMR studies of solutions of hexameric iminolithium compounds, (R1R2CNLi)6
Authors: Barr Donald , Snaith Ronald , Mulvey Robert E. , Wade Kenneth , Reed David
Published: May 2005

Variable‐temperature 7Li and proton NMR spectra of four hexameric (in the solid state) iminolithium compounds, (R1R2CNLi)6 [where R1 = Me2N,R2= Ph (1), R1 = R2 = Me2N (2), R1 = But, R2 = Ph (3) and R1 = R2 = But (4)], recorded for toluene‐d8, solutions of differing concentrations, are described, and the results are discussed with respect to known solid‐state structures. Complex equilibria, probably involving trimeric units and higher aggregates than hexamers, have been detected at low temperatures for solutions of 1 and 2, although similar equilibria do not occur, or are too rapid to detect even at the lowest temperatures attainable, for solutions of 3 and 4.
Solid‐state13C NMR study of drugs: Aspirin
Authors: Chang Ching‐Jer , Díaz Luis E. , Morin Frederick , Grant David M.
Published: May 2005

Natural abundance13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high‐power decoupling, cross‐polarization and magic angle spinning. Solid‐state NMR of aspirin had excellent sensitivity compared with liquid‐state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non‐protonated carbons. The solid‐state13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic.

The solid‐state13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.
1H, 13C, 17O and 33S NMR investigation of some cyclohexyl phenyl sulphides, sulphoxides and sulphones
Authors: Duddeck Helmut , Korek Uwe , Rosenbaum Doris , Drabowicz Jozef
Published: May 2005

The 1H and 13C NMR signals of cyclohexyl phenyl sulphides, sulphoxides and sulphones were almost completely assigned, and the effects of diastereotopism in cis‐4‐tert‐butylcyclohexyl phenyl sulphoxide were rationalized. Substituent effects on the 17O chemical shift of numerous sulphoxides and sulphones are discussed. An unusual paramagnetic γ gauche effect on the 33S nucleus was detected in cis‐4‐tert‐butylcyclohexyl phenyl sulphone.
Reinvestigation of the structural assignment of signals in the 1H and 13C NMR spectra of the flavone apigenin
Authors: Van Loo Piet , De Bruyn André , Buděšínský Miloš
Published: May 2005

The assignment of some 1H and 13C NMR chemical shifts of apigenin have been uncertain and even contradictory. A reinvestigation with recent NMR techniques has led to a new set of 13C NMR parameters and confirmed the accepted 1H NMR data.
15N NMR investigation of the tautomeric equilibria of some 1,2,4‐triazoles and related compounds
Authors: Bojarska‐Olejnik Elzbieta , Stefaniak Lech , Witanowski Michal , Webb Graham A.
Published: May 2005

15N NMR shielding data for some 3‐methoxy‐1,2,4‐triazoles and related triazolones are reported. Assignments are given with the assistance of some INDO/S parameterized SOS shielding calculations. From the 15N NMR shielding results it is possible to give a quantitative account of some potential prototropic tautomeric equilibria.
Carbon‐13 NMR studies in the polycyclic hydrocarbon series. A new method for the identification of carbons α to a carbonyl group. Complete assignment of the 13C NMR spectra of several cis‐decalins, cis‐decalones, cis‐hydrindanones and 13α,14α‐ and 13β,14β‐steroids
Authors: Gramain J. C. , Quirion J. C.
Published: May 2005

A new 13C NMR method based on solvent effects allows the identification of carbon atoms α to a carbonyl group. With a simple change in solvent from CDCl3 to CDCI3‐dioxane (1:4), the 13C absorption for all earbons except those α to the carbonyl group in the compounds under study were displaced to lower field by 0.2–0.5 ppm. The α‐carbon absorptions either remained unchanged or were shifted to higher field by ca 0.1 ppm. The validity of the method has been checked on compounds with fully assigned 13C NMR spectra (trans‐decalones and steroids). Moreover, no modification of these solvent shifts due to the presence of other common functional groups (double bond or OH) was observed. This new technique, together with existing ‘classical’ methods (‘off‐resonance’ spectra, substituent effects) enables the complete interpretation of the 13 C NMR spectra of five cis‐decalins and cis‐decalones to be made. The spectra of three cis‐hydrindanones which have not been previously described were also fully interpreted.

The same method allows the complete spectral assignment of the 13C NMR spectra of six steroids of unnatural configuration in the 13α,14α‐ and 13β,14β‐androstane series, for which no data were previously available.
On‐line NMR in process engineering
Authors: Neudert R. , Ströfer E. , Bremser W.
Published: May 2005

The basis of the evaluation of chemical processes is a comprehensive knowledge about the concentration profiles of the reactants as a function of time. Normally, analytical samples are taken from the reaction medium, with the disadvantage that the analysis does not occur on the reaction time scale and the reaction equilibrium itself is disturbed. For this reason, an on‐line analytical system based on the coupling between an NMR spectrometer and a chemical reactor was developed.

The applicability of the system is demonstrated on a Wittig reaction, the last step in the synthesis of retinoic acid. 31P NMR was employed for the detection of the time dependent concentration of phosphorylated reaction components. The consequences of the results with respect to a change of the chemical process are discussed.
Quantitative analysis of pyrrolizidine alkaloid mixtures from Senecio vulgaris by carbon‐13 nuclear magnetic resonance spectroscopy
Authors: Pieters L. A. C. , Vlietinck A. J.
Published: May 2005

A 13C NMR method has been developed for obtaining simultaneously structural and quantitative information on mixtures of pyrrolizidine alkaloids from Senecio vulgaris L. (Compositae). The samples contained seneciphylline, senecionine, retrorsine and the corresponding E geometrical isomers, spartioidine, integerrimine and usaramine. The spin‐lattice relaxation times were measured and, after establishing the instrumental requirements for quantitative 13C FT NMR, all the alkaloids of the mixture could be determined. Quantitative 1H and 13C FT NMR analyses were carried out, and the advantages and limitations of these methods are discussed.
High‐resolution proton magnetic resonance spectra of morphine and its threeO‐acetyl derivatives
Authors: Neville George A. , Ekiel Irena , Smith Ian C. P.
Published: May 2005

High‐resolution1H NMR (500 MHz) spectra were recorded for morphine, 3‐O‐acetylmorphine, 6‐O‐acetylmorphine and diacetylmorphine (heroin). Complete assignment of all proton resonances was made for these substances following determination of accurate chemical shift and coupling data by spectral simulation of all tightly coupled proton resonance patterns. Chemical shifts and proton couplings are discussed in terms of the conformation of rings C and D. From a varied collection of morphine analogs, torsion angles for ring D protons were obtained from crystallographic studies. The corresponding coupling constants were calculated, they demonstrate similar conformation of the ring D for the compared morphine compounds.
ENDOR studies of semiquinone radical ions in liquid crystalline solutions
Authors: Kirste Burkhard
Published: May 2005

Studies of a series of substituted benzo‐, naphtho‐, anthra‐ and phenanthrene‐semiquinones, benzil semidione and Wurster's blue perchlorate by ENDOR spectroscopy in liquid crystalline solutions are reported. Sufficient solubility of the radical anions is achieved by using lipophilic counter ions such as benzyltrimethylammonium. The effects of ion pairing were investigated, particularly in the case of benzil semidione, which can adopt cis or trans configurations. The anisotropic hyperfine shifts observed in nematic or smectic phases are interpreted by means of calculated dipolar hyperfine tensors. A detailed picture of the alignment of the radical ions in liquid crystalline solvents is obtained. The calculated hyperfine tensors are checked for consistency with experiment, and in some cases compared with measurements in solid solution.
Carbon‐13 NMR spectra of some pseudoguaianolides
Authors: Delgado Guillermo , Alvarez Laura , Huerta Eduardo , de Vivar Alfonso Romo , Mata Rachel
Published: May 2005

The 13C NMR resonances of a series of pseudoguaianolides are reported, which have been assigned on the basis of multiplicities, chemical shift theory and comparison with related substances.
Nuclear magnetic resonance study of the configurational equilibria of ranitidine in solution
Authors: Geraldes Carlos F. G. C. , Gil Victor M. S. , Teixeira M. Helena S. F. , Teixeira F.
Published: May 2005

The E/Z configurational equilibrium of the nitroethylenic moiety of the antiulcer agent ranitidine was studied in aqueous solution and in DMSO‐d6 and CDCl3 using 1H and 13C NMR spectroscopy. In aqueous solution the room temperature E/Z isomerization of the unprotonated nitroketenediamine moiety is fast on the NMR time scale, but becomes slow for the species protonated at this moiety owing to intramolecular hydrogen bonding between the nitro group and a neighbouring NH2R+ group. In DMSO‐d6 a free energy of activation of the order of 70 kJ mol−1 was estimated for the E/Z isomerization of the unprotonated moiety of ranitidine, in good agreement with values previously found for 2,2‐disubstituted nitroethylene model compounds.
17O NMR studies of torsion angle relationships in aryl alkyl ketones and aromatic aldehydes
Authors: Boykin D. W. , Balakrishnan P. , Baumstark A. L.
Published: May 2005

17O NMR spectroscopic data, at natural abundance, in acetonitrile at 75 °C were obtained for a series of phenyl alkyl and cycloalkyl ketones, benzophenone, methyl alkyl ketones, three fused‐ring aryl ketones and a series of variously hindered aromatic aldehydes. The trend in chemical shifts for the relatively unhindered alkyl aryl ketones is a general increase in shielding with increasing size of the alkyl group. However, when steric hindrance becomes significant, torsion angle rotation occurs and deshielding is observed. Cyclopropyl ketones show much larger shielding effects than their isopropyl analogs. Torsion angles for aryl ketones and aromatic aldehydes are estimated using an indirect method based on previous results from electronically similar hindered ketones.
Significance testing of lanthanide shift reagent data
Authors: Ribó Josep M. , Valera GeníS
Published: May 2005

The use of weighted agreement factors in the significance testing of lanthanide‐induced shift analysis is physically meaningless, and can manipulate the resulting significance values, as confirmed by the results found with two compounds. The Hamilton ℛ factor ratio significance test and the jacknife test are compared for these compounds. The ℛ ratio test is more easily applied; the jacknife test does not show any clear advantage and is more sensitive to changes originating from the use of weighted agreement factors.
Study of the prototropic tautomerism of 8‐azatheophylline by 13C and 15N NMR spectroscopy
Authors: L'abbé Gerrit , Persoons Marie‐Anne , Toppet Suzanne
Published: May 2005

Comparison of the 13C and 15N NMR spectra of 8‐azatheophylline with those of its three methylated derivatives and other model compounds from the literature showed that 8‐azatheophylline exists to the extent of 80% in the N‐2 tautomeric form in DMSO solution.
Origins of phase anomalies in 13C FT NMR spectra
Authors: Anet Frank A. L. , Zheng Li Kao , Zhihong Tan
Published: May 2005

Some controversy exists on the origin(s) of phase anomalies observed in 13C FT NMR spectra. Two separate explanations, based on either echo or sampling effects, have been proposed by previous workers. We now show experimentally that these two effects can occur separately or together and, in the latter case, the effects can interfere with one another. Methods to ameliorate or remove phase anomalies are briefly reviewed.
1H and 13C nuclear magnetic resonance study of 1,3‐dipyridylthioureas for chemical shift assignments and conformational analysis
Authors: Sudha L. V. , Sathyanarayana D. N. , Bharati S. Narasimha
Published: May 2005

A study of molecular conformation by 1H and 13C NMR methods of three 1,3‐dipyridyl thioureas namely, 1,3‐di(2‐pyridyl)thiourea (1), 1,3‐di(3‐pyridyl)thiourea (2), 1‐(2‐pyridyl)‐3‐(3‐pyridyl)thiourea (3), and also of 1‐phenyl‐3‐(2‐pyridyl)thiourea (4) and 1,3‐diphenylthiourea (5), included for the sake of comparison, was carried out. Evidence was obtained that 3 and 4 exist in solution solely in one form, in an internally hydrogen bonded E,Z conformation, whereas 1, 2 and 5 exist in two (or more) rotamer forms. The data reveal an interesting dynamic exchange phenomenon occurring in 1 between two intramolecularly hydrogen bonded conformers. The 1H and 13C chemical shifts, 1H,1H and 13C,1H coupling constants are reported. The 13C and 1H chemical shifts are correlated with the electron densities calculated by the CNDO method.
13C NMR spectra of some sulphur dioxide—aromatic amine complexes
Authors: De Faria D. L. A. , Santos P. S.
Published: May 2005

The 13C NMR spectra of equilibrium mixtures formed between sulphur dioxide and N‐methylbenzenamine, N,N‐dimethylbenzenamine and N,N‐diethylbenzenamine were obtained. The analysis of the spectral data indicates that the interaction of the amines with the Lewis acid occurs by means of the lone pair mainly localized on the nitrogen atom, and that the complexes can be considered as labile on the time scale of the experiment.
ESR and theoretical study of tetrathiofulvalene and dibenzotetrathiofulvalene and their radical cations
Authors: Hibbert D. Brynn , Hamedelniel Abdelrazik E. , Sutcliffe Leslie H.
Published: May 2005

The three semi‐empirical methods MNDO, AM1 and MINDO/3 have been used to determine geometries, ionization potentials and spin densities of tetrathiofulvalene, dibenzotetrathiofulvalene and their radical cations. ESR measurements of the cation radicals both in solution and the solid states provided experimental spin densities. A comparison is made between calculated and experimental data; it appears that MINDO/3 is superior for the calculation of spin densities.
13C NMR Data [δ(13C), 1J(C,H), 1J(C,C)] of some bicycloalkenes
Authors: Benn R. , Butenschön H. , Mynott R. , Wisniewski W.
Published: May 2005

The 13C shifts of the bicyclo[3.2.0]alkenes 1‐7, spiro[2.4]hepta‐4,6‐diene (8) and the bicyclo[3.3.0]octenes 9 and 10 have been assigned via one‐ and two‐dimensional INADEQUATE experiments. The values of 1J(C,H) and 1J(C.C) of 1‐10 are also reported.
Stereochemistry of the B/C ring junction in 3‐benzylidenebenzo[a] quinolizidines
Authors: Hajpál I. , Scheiber P. , Nádor K.
Published: May 2005

A trans B/C ring junction has been found to exist in 3‐benzylidinebenzo[a]quinolizidines. 1H NMR analysis of partially deuteriated compounds showed that the signals at 4.0‐4.2 ppm should be assigned to the H‐4‐exo proton.
13C NMR spectroscopy of (25R)‐5α‐spirostanes
Authors: García José Alberto Ruiz , Castro Hermán T. Vélez
Published: May 2005

The 13C NMR spectra of sixteen (25R)‐5α‐spirostanes have been examined, and the substituent effects on the 13C chemical shifts are discussed.
Two‐dimensional 1H and 13C‐NMR spectra of 5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene, its precursor and metabolite
Authors: Lyčka Antonin , Jirman Josef , Nobilis Milan , Kvasničková Eva , Hais Ivo M.
Published: May 2005

The 1H and 13C chemical shifts in 5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene (1) and 5‐hydroxy‐7‐oxo‐7H‐benzo[c]fluorene (2) were assigned using H,H‐COSY, H,C‐COSY and selective INEPT spectra. It was found that the main phenolic metabolite of 1 and its hydrochloride corresponds to 9‐hydroxy‐5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene (3).
Solution structure of porphyrin aggregates determined by 1H NMR ring current shifts. I. Heterodimers of oppositely charged porphyrins
Authors: Hofstra U. , Koehorst R. B. M. , Schaafsma T. J.
Published: May 2005

The solution structures of dimers consisting of negatively charged Zn[tetra(4‐carboxyphenyl)porphyrin], ZnTPPC, with positively charged Zn[tetra(4‐N‐methylpyridyl)porphyrin], ZnTMPyP, and with H2[tetra(4‐N‐methylpyridyl)porphyrin], H2TMPyP, were determined by 1H NMR ring current shifts. The conformation is not affected by the presence of the metal in the centre of the TMPyP monomer. The dimers have a cofacial conformation with a plane‐to‐plane separation of 3.1 Å and an in‐plane translation of 4.2 Å along the aryl—aryl axis.
Use of 13C1H coupling constants for the investigation of azide—tetrazole tautomerism in aromatic nitrogen heterocycles. Detection of ditetrazolo [1,5‐a: 1′,5′‐c:] pyrimidine
Authors: Denisov Aleksei Yu. , Krivopalov Viktor P. , Mamatyuk Viktor I. , Mamaev Vladimir P.
Published: May 2005

The proton‐coupled 13C NMR and 1H NMR spectra of azidobenzene, tetrazolo[1,5‐a]pyridine, 2‐azidopyrimidine and tetrazolo[1,5‐a]pyrimidine in different solvents have been analysed, and criteria for using the NMR spectral parameters (especially the 13C‐1H coupling constants) for tautomeric structure determination have been elaborated. The efficiency of these criteria has been demonstrated in studies of azide‐‐tetrazole equilibria in 2,4‐ and 4,6‐diazidopyrimidines. The ditetrazolo tautomeric form of 2,4‐diazidopyrimidine has been found in polar solvents.
Carbon‐13 and proton two‐dimensional NMR study of diterpenoids of Coleus forskohlii
Authors: Prakash Om , Roy Raja , Tandon J. S. , Dhar M. M.
Published: May 2005

The stereochemical assignments of coleonol‐B (1), coleonol‐D (2) and coleosol (3) were accomplished by 2D 1H1H (COSY), 1H13C (hetero COSY), NOE difference NMR spectroscopic, stereospecific coupling constant and selective heteronuclear spin decoupling studies. The complete 13C chemical shift assignments of 2, 3 and coleol (4) were made for the first time. The earlier 1H chemical shift assignments were corrected and the stereostructure of coleonol‐D was reassigned.
Improvement in the evaluation of quantitative data in FT NMR spectroscopy by the convolution difference resolution enhancement (CDRE) technique
Authors: Kupka Teobald , Dziȩgielewski Jan Olgierd
Published: May 2005

Practical guidelines for obtaining the optimum results in quantitative FT NMR spectroscopy through the use of the convolution difference resolution enhancement (CDRE) method are given. Use of the optimum parameter set diminishes the errors in the integral intensity and the line position measurements caused by poorly resolved signals.
Deuterium‐induced NMR isotope shifts for13C resonance frequencies of norbornane. Quantitative data for the dihedral angle dependence of vicinal shifts
Authors: Aydin Rafet , Frankmölle Walter , Schmalz Dietmar , Günther Harald
Published: May 2005

The complete set of deuterium‐induced intrinsic13C NMR isotope shifts,nΔ(13C), for norbornane have been determined from the isotopomeric monodeuteriated systems, and the results are discussed with respect to structure. No correlation is found between1Δ values and thescharacter of the CD bond hybrid. For vicinal isotope effects, however, a quantitative correlation with the dihedral angles of the intervening13C‐CCD bond fragment can be formulated: |3Δ(13C) | (ppb) = 2.2 + [7.3 × 10−3(ϕ −117.8)2]

Negative3Δ values are found for bonding pathways in the five‐membered ring partial structure with anantiarrangement of the CCCD bond fragment.
Complete carbon‐13 and proton NMR assignments for two mesogenic series containing cyclohexyl rings
Authors: Frech Cheryl Baldwin , Fung B. M. , Schadt Martin
Published: May 2005

Complete 13C and 1H spectral assignments for two series of liquid crystals in CDCl3 solution were made. The 4‐(trans‐4‐alkylcyclohexyl)benzonitriles had propyl‐to pentyl‐substituted alkyl chains, whereas the 4‐(trans‐4‐alkenylcyclohexyl)benzonitriles had varying positions of the alkenyl bond. 13C and 1H chemical shifts and 13C1H scalar coupling constants are reported.
Temperature dependence of NMR secondary references for D2O and (CD3)2SO solutions
Authors: Hoffman R. E. , Davies D. B.
Published: May 2005

Chemical shifts of secondary references for D2O and (CD3)2SO solutions were measured as a function of temperature. The 1H and 13C chemical shifts of dioxane, sodium 4,4‐dimethyl‐4‐silapentanesulphonate, HOD, tetramethylammonium chloride and sodium 3‐(trimethylsilyl)propionate‐d4 in D2O solution were measured relative to external TMS and the chemical shifts of (CD3)2SO and H2O were measured in (CD3)2SO solution relative to internal TMS. For accurate comparison of chemical shifts it is necessary to take into account the sample temperature and, therefore, the temperature dependences of 1H and 13C chemical shifts of a number of secondary references have been determined accurately and fitted to a parabola or straight line, as appropriate.
Restricted rotation in sterically hindered dichalcogenides. A dynamic NMR study
Authors: Pinto B. Mario , Leung Ronald Y. N. , Sharma R. Dev
Published: May 2005

The rotational barriers in bis(2,4,6‐tri‐tert‐butlphenyl) diselenide and ditelluride have been investigated by total line‐shape analysis of variable‐temperature 1H NMR spectra in CFCI3CD2Cl2 (85:15). The free energies of activation, ΔG, for the diselenide and ditelluride were determined to be 49.4 ± 0.6 and 39.2 ± 0.2 kJ mol−1, respectively. The difference is attributed to the dominance of steric effects in the transition state for rotation.
Practicalities and applications of reverse heteronuclear shift correlation: Porphyrin and polysaccharide examples
Authors: Cavanagh John , Hunter Christopher A. , Jones David N. M. , Keeler James , Sanders Jeremy K. M.
Published: May 2005

The practical aspects of proton‐detected heteronuclear shift correlation spectroscopy are described in detail, with emphasis on the precautions necessary to obtain efficient suppression of signals from protons that are not coupled to 13C. The experiment has been used to assign the quaternary carbon signals of a porphyrin and to resolve the proton spectrum of the K3 serotype polysaccharide.
Improvement of relayed—NOESY type experiments by implantation of spin‐lock sequences
Authors: Kessler H. , Gemmecker G. , Haase B. , Steuernagel S.
Published: May 2005

Several Relayed—NOESY type pulse sequences are discussed which use spin‐lock periods for one or both of the two transfer steps. The use of such experiments for the sequence analysis of peptides is shown. The requirements for a successful application of special data processing techniques are explained. Even in conformationally rigid peptides where these conditions are no longer fulfilled, the 2D techniques described represent a sensitive and reliable method for the sequential assignment of the spin systems.
Application of natural abundance 2H NMR. Simultaneous measurement of primary and secondary kinetic deuterium isotope effects
Authors: Zhang Ben‐Li
Published: May 2005

Internal and external reference methods are introduced for the study of kinetic deuterium isotope effects (KDIEs) by natural abundance 2H NMR. These methods take account of both inter‐ and intra‐molecular competive reactions of fully protonated and naturally monodeuteriated molecules of the substrate in the reaction. Specifically deuteriated compounds are not necessary using these methods. These techniques have further advantages over other methods; for example, primary and secondary KDIEs of different types can be measured simultaneously. The methodology is summarized and examples of its application are presented.
Assignment of the 13C NMR shifts of brominated pyrrole derivatives
Authors: Foley L. H. , Habgood G. J. , Gallagher K. S.
Published: May 2005

The 13C NMR chemical shift assignments of unbrominated, monobrominated and dibrominated pyrrole 2‐trichloroketones, esters and amides are presented.
Triazoles. XIV—15N NMR study of substituted 5‐amino‐1,2,4‐triazoles
Authors: Orendt Anita M. , Michl Josef , Reiter József
Published: May 2005

15N NMR chemical shifts were measured for a series of substituted 5‐amino‐1,2,4‐triazoles. The assignment of isomeric structures agrees with earlier results obtained with the use of proton‐coupled 13C NMR.
1H and13C spectra of fluorine‐containing polycyclic aromatic hydrocarbons.1H19F and13C19F coupling across bay regions
Authors: Sardella D. J. , Boger E.
Published: May 2005

The1H and13C NMR spectra of several fluorine‐substituted polycyclic aromatic hydrocarbons in which fluorine projects into a bay region were studied. Both protons and carbons of the sterically opposed CH bond show anomalously large F‐induced shifts and couplings to fluorine. The magnitudes of the couplings (particularly the four‐bond CF couplings which average 26 Hz) indicate a large through‐space contribution due to direct overlap between fluorine and CH bond orbitals, whereas the F‐induced shifts seem more likely to stem from diamagnetic anisotropy rather than F‐induced CH bond polarization.
High‐resolution solid‐state 119Sn and 207Pb NMR study of organotin and organolead chalcogenides: Observation of J‐coupling in solids
Authors: Harris Robin K. , Sebald Angelika
Published: May 2005

High‐power decoupling, cross‐polarization and magic‐angle spinning techniques were used to obtain high‐resolution 119Sn NMR spectra of six organotin chalcogenides. In addition, the 207Pb spectrum of bis(triphenyllead)sulphide was obtained. The data were compared with the results of NMR measurements in solution and are discussed in relation to crystallographic considerations. Satellite resonances allow some metal‐metal coupling constants to be determined. The existence of intramolecular crystallographic inequivalence makes this feasible even for (Ph3Pb)2S. Use of a rotation‐synchronized Carr‐Purcell‐Meiboom‐Gill pulse sequence improves the ability to measure such coupling constants, as is demonstrated for (Me2SnS)3.
Carbon‐13 NMR studies of acridine derivatives. Part VII.—13C chemical shifts of some substituted 9‐acridanones and 9‐thioacridanones
Authors: Faure R. , Galy J. P. , N'Gadi L. , Barbe J.
Published: May 2005

13C NMR data are presented for 31 variously substituted derivatives of 9‐acridanone and 15 derivatives of 9‐thioacridanone. Unexpected shifts are explained in terms of hydrrgen bonding or tautomeric equilibria.
13C NMR structural analysis of a series of tricarbony(diene)iron complexes
Authors: Rodriguez J. , Brun P. , Zahra J. P. , Waegell B.
Published: May 2005

The 13C NMR spectra of two series of substituted tricarbonyl(cyclohexadiene)iron complexes and of subsitituted tricarbonyl(vinylcyclohexene)iron complexes were recorded; 1‐ and 2‐substituted complexes can be distinguished by chemical shift comparison with parent compound.
Experimental and theoretical study of the methoxy group conformational effect on 13C chemical shifts in ortho‐substituted anisoles
Authors: Biekofsky Rodolfo R. , Pomilio Alicia B. , Econteras Ruben H. , de Kowalewski Dora G. , Facelli Julio C.
Published: May 2005

Aromatic 13C chemical shifts are reported for a number of ortho‐substituted anisoles. Quantitative determination of the substituent chemical shift (SCS) effects of the methoxy group with a fixed coplanar conformation on aryl carbon nuclei was achieved using experimental and theoretical methods. The experimental values were compared with those calculated through the use of the additivity, and a systematic departure from additivity was found for carbon nuclei in ortho positions. Ortho‐SCSs were found to be non‐equivalent, and the ortho effect on the carbon cis to the fixed methoxy moiety was more shielding than in anisole. The IGLO (Individual Gauge for Localized Orbitals) method was used to calculate the SCSs. Experimental and theoretical trends obtained for the influence of the side‐chain conformations on chemical shifts are in very good agreement with each other, and with recent results obtained by solid‐state NMR.
Analysis of the carbon and proton NMR spectra of 2‐arylthiophenes and related heterocycles
Authors: Del Mazza Dario , Reinecke Manfred G. , Smith William B.
Published: May 2005

Complete proton and carbon NMR assignments were made for five 2‐(2‐X‐phenyl)thiophenes (X = NH2, NO2, COOH, Br), four 2,5‐diphenylheterocycles (thiophene, furan and N‐methyl‐ and N‐phenylpyrrole) and N‐phenylpyrrole using HETCOR, COSY, XCORFE and, in one case, NOESY 2D NMR techniques. In the first set of compounds a good correlation was found between the chemical shifts of certain carbon atoms and σp and/or the Q‐parameter. In the second series the expected correlation with the aromatic character of the heterocycle was observed primarily with the furan compound, where the heterocyclic ring strongly increases the electron density of the phenyl rings.
1H and 13C dynamic NMR study of the E, Z isomers of vinylogous diamides. Effect of conjugation and electrostatic and steric repulsion on the C(O)N rotation barriers and low‐temperature conformation
Authors: Szalontai Gábor , Sándor Péter , Bangerter Felix , Kollár László
Published: May 2005

A 1H dynamic NMR study was carried out on N,N‐diethylmethacrylamide (1a), N,N,N′,N′‐tetraethylitaconamide (2), N,N,N′,N′‐tetraethylcitraconamide (3) and N,N,N′,N′‐tetraethylmesaconamide (4) over a wide temperature interval. Amide rotational barriers were determined from the coalescence temperatures. In 3 a second dynamic process was observed below 240 K, which made the geminal methylene protons non‐equivalent. The phenomenon is interpreted in terms of a non‐planar conformation caused by electrostatic and/or steric repulsion of the amide carbonyls. Homonuclear NOE experiments revealed an s‐cis, s‐cis′ conformation for the compounds studied.
1H and 13C NMR study of the interaction of formaldehyde on adenine and its derivatives
Authors: Le Botlan D. J.
Published: May 2005

It has previously been shown that formaldehyde causes the formation of hydroxymethylated derivatives with nucleobases, but these were identified after separation of the reaction products; such handling might destroy labile derivatives or remove products present in small proportions. This work is based on a study of the reactivity of formaldehyde on adenine, adenosine and adenosine monophosphate in the reaction medium. It demonstrates the high reactivity of the N‐9 site of adenine, the reactivity of the hydroxymethyl at the C‐5′ of the ribose and brings to light such new derivatives as N‐9‐CH2OCH2OH and N‐6‐CH2OCH2OH. Further, the order of appearance of different derivatives and their approximate determination were achieved.
NMR study of substituent effects in 4‐substituted and 4,4′‐disubstituted diphenyl sulphoxides and sulphones
Authors: Chandrasekaran R. , Perumal S. , Wilson D. A.
Published: May 2005

The proton and carbon NMR spectra of nine 4‐X‐diphenyl sulphoxides, seven 4‐X‐4′‐NO2‐diphenyl sulphoxides, eight 4,4′‐X2‐diphenyl sulphoxides, eight 4‐X‐diphenyl sulphones, seven 4‐X‐4′‐NO2‐diphenyl sulphones and eight 4,4′‐X2‐diphenyl sulphones have been obtained. Correlation of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes (Lynch plots) does not show the enhancement of substituent effect at C‐1 (para to the substituent) that was a feature of the corresponding sulphides studied earlier. Dual substituent parameter (DSP) correlations of the 13C chemical shifts with σ1/σR0 are excellent for carbons meta (C‐2,6) and para (C‐1) to the substituent. The trends for the series sulphides, sulphoxides, sulphones, where a decreasing response to the change of substituent is the general observation, are discussed. Changes of molecular conformation may also influence the transmission of electronic effects to the ring not carrying the variable substituent X.
NMR spectra and conformational analysis of substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives
Authors: Malik Farnaz , Hassan Mashooda , Rosenbaum Doris , Duddeck Helmut
Published: May 2005

An investigation of the molecular dynamics of substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives revealed that these molecules adopt cycloheptadiene‐like boat conformations. There is an equilibrium between the quasi‐axial and the quasi‐equatorial conformer in which the quasi‐axial conformer is predominant. The difference in their conformational energies is less than 1 kcal mol−1. The most important factor influencing the energy barrier between the conformers is the presence of a substituent other than hydrogen at N‐1. Our findings disprove earlier reports by other workers.
Quantitative small molecule NOESY. A practical guide for derivation of cross‐relaxation rates and internuclear distances
Authors: Andersen Niels H. , Eaton Hugh L. , Lai Xiaonian
Published: May 2005

The pure absorption 2D NOE experiment can provide small molecule cross‐relaxation rate data suitable for quantitative conformational analysis even when the data are collected in a time‐saving manner using preparatory delays (PD) far short of the recommended values of 3–5 times T1. In our experience, the relative NOE intensities and cross‐relaxation rates are most readily extracted from cross‐relaxation spectra which are sums of adjacent rows (or columns) of the 2D data matrix. Intensity anomalies associated with t1 streaks can be removed by plotting cross‐relaxation difference spectra. PD truncation produces significant deviations from diagonal symmetry which must be accounted for in the data analysis. The influence of PD truncation on apparent auto‐peak decay rates and cross‐/auto‐peak intensity ratios is examined in both real and simulated spectra in order to develop appropriate quantitation strategies. These strategies, when applied to NOESY data for aqueous prostaglandin (PG) F2 α and a PG analog in organic media, yield cross‐relaxation rates that are within experimental error of those calculated from structural models or determined by more time‐consuming 1D NOE methods.
13C and 1H NMR investigations of quinic acid derivatives: Complete spectral assignment and elucidation of preferred conformations
Authors: Flores‐Parra Angelina , Gutiérrez‐Avella Dora Marina , Contreras Rosalinda , Khuong‐Huu Françoise
Published: May 2005

The 1H and 13C NMR spectra of 23 quinic acid derivatives are reported. The complete assignment of the 1H NMR spectra using selective proton decoupling experiments allowed the conformation of the six membered ring to be established from vicinal coupling constants and the calculation of dihedral angles. The 13C spectral assignments were made by consideration of substituent effects and comparison within the series. In some cases the similarities in chemical shifts did not allow unambiguous assignments; the chemical shifts were then calculated from empirical parameters.
Quantitative evaluation of electronic effects of the 1‐tetrazolyl group from1H and13C NMR data for substituted 1‐phenyltetrazoles
Authors: Karavai Vladimir P. , Gaponik Pavel N. , Ivashkevich Oleg A.
Published: May 2005

The1H and13C NMR spectra of severalmeta‐ andpara‐substituted 1‐phenyltetrazoles have been recorded, and the observed chemical shifts used for (i) the evaluation of σp, σm, σI, σRand σR°, the Hammett and Taft values of the 1‐tetrazoyl group, and (ii) the transmission of the electronic effects of themetaandparasubstituents on the phenyl ring to the tetrazole carbon and hydrogen atoms.
NMR spectroscopy of paramagnetic complexes. Part 36—2/1H NMR of paramagnetic metallocenes: Primary and secondary isotope effects and signal narrowing
Authors: Hebendanz Nikolaus , Köhler Frank H. , Scherbaum Franz , Schlesinger Björn
Published: May 2005

1H and 2H NMR spectra were recorded for the paramagnetic metallocenes Cp2M (M = V, Cr, Mn, Co, Ni). For Cp2V, Cp2Cr, Cp2Mn and Cp2Ni, a signal narrowing factor of 36–37 is observed on going from Cp2M‐h10 to Cp2M‐d10, which is close to simple theoretical predictions. Additional quadrupolar relaxation leads to a factor of 27 for cobaltocene. The enhanced resolution of the 2H NMR spectra makes it possible to observe isotopomeric cobaltocenes with signals showing a secondary isotope shift of 0.71 ppm. In Cp2 Co‐d9 and ‐d8, the residual 1H atoms lead to a splitting of the 2H NMR signals, which is traced to the lifting of an orbital degeneracy due to the perturbation of the ligand π‐system by the lighter isotope. Primary isotope shifts of 2.33, 1.24, and 1.45 ppm are found for the pairs Cp2Mn‐d10/h10, Cp2Co‐d10/h10 and Cp2Ni‐d10/h10. They reflect a change in the electron spin distribution after complete deuteriation.
Study of hydrolytic kinetics of the hexachlorostannate anion by two‐dimensional 119Sn exchange spectroscopy
Authors: Mao Xi‐An , You Xiao‐Zeng , Dai An‐Bang
Published: May 2005

Two‐dimensional 119Sn exchange spectroscopy was applied to study the hydrolytic kinetics of the hexachloro‐stannate anion, SnCl62−. Two 119Sn exchange spectra for SnCl4 · 5H2O solutions with various HCl concentrations are presented. Magnetization exchanges, which are related to the hydrolysis processes, occur in the SnCl62− hydrolysis series. The exchange rate constants, the hydrolysis rate constants and the hydrolysis equilibrium constants were evaluated.
13C NMR studies of insulin. Part I—Spectral assignments
Authors: Craik David J. , Higgins Kerry A. , Hall Jon G. , Andrews Peter R.
Published: May 2005

Natural abundance 75 MHz 13C NMR spectral assignments are reported for bovine and porcine zinc insulin in solution. A large number of protein resonances are well resolved, and approximately 80% of these have been assigned to either residue types or to specific sites within the protein. Assignment techniques included consideration of free amino acid or peptide shifts pH studies and comparison of sequence and spectral differences between bovine and porcine insulin, in addition to the use of NMR relaxation times. The DEPT spectral editing technique was also found to be particularly valuable as an assignment aid. This technique allows subspectra containing only CH, CH2 or CH3 carbon types to be generated. The method also produces signal enhancement relative to broad band decoupled 13C NMR spectra of large proteins which generally have reduced nuclear Overhauser enhancements.
Complete 1H and 13C NMR spectral assignment of venturicidin A by 2D NMR spectroscopy
Authors: Gogoll Adolf , Tanner David
Published: May 2005

After correlation of the majority of signals by COSY and one‐bond heteronuclear correlation, the complete assignment of the 1H and 13C NMR spectra of the macrolide antibiotic venturicidin A required the application of long‐range CH coupling information. This was accessible by the COLOC‐S and selective INEPT experiments, and the sensitivity of these experiments is discussed. Steric information was obtained from a NOESY spectrum, and the solution structure compared with that in the crystal.
Exceptional resolution and new signals detected in the 13C NMR spectra of alkanes
Authors: Alemany Lawrence B.
Published: May 2005

The relative ease with which very high resolution 13C NMR spectra can now be obtained because of advances in NMR technology is shown. Spectra of four alkanes were obtained at 62.9 MHz with careful shimming, low‐power decoupling and a digital resolution of less than 0.1 Hz. Signals as little as 3 ppb apart can be clearly distinguished at this moderate field strength without resolution enhancement. Consequently, additional information can be obtained. For n‐hexadecane, six, not the usual five, signals are evident; the chemical shifts of C‐6, C‐7 and C‐8 are within 0.16 Hz (2.5 ppb) of each other and are not all the same. For 2‐methyltridecane, all 13 signals are visible; all the signals can be assigned with confidence except those for C‐7 and C‐8, which differ by only 4 ppb. For 7‐ methylhexadecane, all 17 signals are visible; many can be assigned to a specific carbon, including the signals for C‐3 and C‐14 (both of which are in CH3CH2CH2CH2CH2CH2— environments), which differ by only 37 ppb. For the two pairs of enantiomers of 2,6,10‐trimethyldodecane, all but one carbon give a pair of resonances; the two signals for C‐3 are only 2.9 ppb apart. The potential limitations on molecular size and field strength affecting line width are considered. The same solvent, concentration and temperature must be used if chemical shift data for different compounds are to be meaningfully compared in detail.
Two‐dimensional NMR analysis of selected benzazolo[3,2‐a]quinolinium salts
Authors: Cox Osvaldo , Prieto Jose A. , Rodriguez Margarita
Published: May 2005

1H and 13C studies of selected benzazolo[3,2‐a]quinolinium salts were carried by two‐dimensional NMR methods. The assignments of the 1H resonances were made by 2D homonuclear shift correlation (COSY) and the 2D nuclear Overhauser effect (NOESY). Complete 13C chemical shift assignments were carried out by using DEPT and two‐dimensional heteronuclear correlation spectroscopy.
13C NMR of lapachol and some related naphthoquinones
Authors: Dawson Brian A. , Girard Michel , Kindack Daryl , Fillion Julie , Awang Dennis V. C.
Published: May 2005

13C NMR chemical shift assignments for lapachol and nine related naphthoquinones have been measured and interpreted. Data, based on the results of a number of 1D and 2D experiments performed at 9.4 T, correct several previously reported assignments for some of these compounds.
Solution conformations of 1‐anilinonaphthalene‐8‐sulphonate
Authors: Mendz George L. , Vandenberg Robert J. , Easterbrook‐Smith Simon B.
Published: May 2005

The Conformations and dynamics of 1‐anilinonaphthalene‐8‐(ANS) in solutions of solvents with different polarities and hydrogen‐bonding properties were investigated by high‐resolution 1H and 13C NMR spectroscopy. Two‐dimensional correlated spectrocopy, tirations with paramagnetic ions and one‐dimensional spin‐decoupling techniques were employed t assign the spectra observed from both nuclei. Nuclear Overhauser effect data provided evidence that the fluorohore adopts compact conformations in the more pola solvents. 13C spin‐lattice relaxation times indicated that the benzene ring of ANS has a degree of internal mobility in the solutions of all the solvents studied. Measurement of Stokes shifts in different solvents that the special fluorescence properties of ANS in aqueous solutions arise from the proton donor character of the solvent rather than from its polarity or the conformational flexibility of the fluorophore.
Chiral hydroxymethyl groups: 1H NMR assignments of the prochiral C‐5′ protons of 2′‐deoxyribonucleosides
Authors: Kline Paul C. , Serianni Anthony S.
Published: May 2005

2′‐Deoxyadenosine, 2′‐deoxycytidine, 2′‐deoxyguanosine and 2′‐deoxyuridine were prepared with stereoselective deuteriation at C‐5′ and used to assign the prochiral C‐5′ protons in 300 MHz 1H NMR spectra obtained in 2H2O. In all cases, the more shielded C‐5′ proton was found to be the pro‐R proton. From these assignments, C‐4′–C‐5′ rotamer populations were determined using three previously published methods based on the spin couplings, 3J(H‐4′,H‐5′R) and 3J(H‐4′,H‐5′S), and the errors associated with these methods were assessed. The effects of base structure, furanose and N‐glycoside bond conformation on the relative populations of hydroxymethyl rotamers in nucleosides are discussed.
A novel approach for evaluating the NMR spectra of spinning solids: Application to the case of chemical exchange
Authors: Frydman Lucio , Frydman Benjamin
Published: May 2005

An approach is introduced that allows the evaluation of the effects of magic‐angle spinning (MAS) in the NMR spectra of inhomogeneously broadened spin‐1/2 nuclei. The method, which consists in replacing the time‐dependent MAS Hamiltonian by a set of three time‐independent Hamiltonians, is able to predict one of the main characteristics of the MAS experiment, namely the appearance of rotor echoes. Spectra were calculated using this approach and compared with 13C NMR spectra of model compounds, showing good agreement in the range of spinning rates normally used. A simple extension of the method also makes it useful for simulating some cases of variable‐angle spinning NMR. Although the approach is suitable for the evaluation of normal MAS NMR spectra, its main applications may be found in cases where the spin Hamiltonian is no longer self‐commuting. As an example, the method was employed for analysing the case of an exchange process between two equally populated chemically equivalent sites. Calculated spectra obtained in this way allowed the correct reproduction of the changes observed in the MAS NMR spectra of two compounds which are known to undergo reorientations in the solid state. Further possible applications of the approach are discussed.
13C and 31P solid‐state NMR studies of bis(dialkoxythiophosphoryl) disulfides
Authors: Chu Po‐Jen , Potrzebowski Marek J.
Published: May 2005

The principal elements of the chemical shift tensors for the phosphorus atoms in three bis(dialkoxythiophosphoryl) disulfides were determined from both static and magic angle spinning NMR spectra, using the intensities of the peaks in the spinning sidebands relative to those of the central band in the latter method. These studies show that it is possible to deduce a mode of molecular motion in the solid state by analysis of the shielding parameters. Variable‐temperature 13C and 31P CP MAS NMR of these samples from 190 to 320 K revealed a peculiar motion of the methoxy group and a rigid PSSP backbone for bis(dimethoxythiophosphoryl) disulfide. In addition, these studies confirmed that it is possible to distinguish the different x‐ray crystal structures from the solid‐state NMR experiment.
17O NMR study of steric hindrance in methoxylated flavones. Substitution on the phenyl ring and the heterocycle
Authors: Wallet Jean‐Claude , Gaydou Emile M. , Cung M. T.
Published: May 2005

Natural abundance 17O NMR spectra were recorded for ten methoxyflavones and one flavonol. The chemical shifts are discussed in terms of steric and conformational changes. They are related to previously reported 13C NMR data.
Occurrence of β‐bends in bradykinin dissolved in DMSO‐d6
Authors: Mirmira Suman R. , Durani S. , Srivastava Sudha , Phadke Ratna S.
Published: May 2005

The conformation of the hormone bradykinin (Arg–Pro–Pro–Gly–Phe–Ser–Pro–Phe–Arg) in DMSO‐d6 was investigated using proton NMR spectroscopy at 500 MHz. Complete resonance assignments were made using 2D COSY and NOESY techniques. The chemical shifts, magnitudes of the 3JNH‐CαH couplings, temperature coefficient data on backbone NH protons and intramolecular NOEs were used to obtain information on the conformation. The nonapeptide assumes a rigid structure in DMSO‐d6. Based on the experimental results, a model is proposed using computer‐aided molecular graphics.