bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of stability constants of metal complexes from NMR chemical shifts and relaxation rates using a spreadsheet computer program
Authors: Huskens Jurriaan , Lammers Hendrik , van Bekkum Herman , Peters Joop A.
Published: May 2005

The versatility of multinuclear magnetic resonance techniques in the determination of stability constants of metal complexes is demonstrated for three cases in which potentiometry is impossible or less suitable. The complexation of cyclo‐trimetaphosphate to lanthanide aminopolycarboxylate complexes was investigated in a dilution experiment using 31P NMR shifts. The stabilities of CdL and CdL2 [L = 1‐(2‐aminoethylamino)‐1‐deoxy‐D‐galactitol] were determined by 113Cd NMR speciation, in which the occurring species were in slow exchange. Competition experiments using both 31P NMR shifts and 13C and 31P relaxation rate enhancements were performed to determine the stabilities of Nd(NTA)(PPP) and Nd(PPP)2 (PPP = tripolyphosphate). Where possible, the results were compared with potentiometric data and found to be in good agreement.
15N NMR chemical shifts of NH‐pyrazoles in the solid state and in solution at low temperature
Authors: Aguilar‐Parrilla Francisco , Männle Ferdinand , Limbach Hans‐Heinrich , Elguero José , Jagerovic Nadine
Published: May 2005

The 15N chemical shifts of thirteen NH‐pyrazoles in the solid state and of seven NH‐pyrazoles in [2H8] THF solution at 170–175 K (with frozen annular tautomerism) are reported. The solid‐state values are discussed using an additive model. The differences in chemical shifts between the solid state and solution are due to the different intermolecular hydrogen bonds present in the various environments.
Preparation and NMR determination of structures of tri‐, tetra‐ and pentacyclic isoindolone derivatives
Authors: Sohár Pal , Frimpong‐Manso Samuel , Stájer Géza , Bernáth Gábor
Published: May 2005

From the reactions of 3‐endo‐benzoyl‐6‐exo‐phenylbicyclo[2.2.1] heptane‐2‐endo‐carboxylic acid (2) and α,ω‐diamines or o‐aminophenol/thiophenol, different tri‐, tetra‐ and pentacyclic phenyl‐substituted norbornane‐condensed heterocycles were prepared. With ethylenediamine, 2 furnished two isomeric imidazolo[2,1‐a]isoindolones. In the formation of one of them, an end→oexo isomerizaton was observed. The stereostructures (configurations and conformations) of the compounds were elucidated by 1H and 13C NMR spectroscopy, with the aid of routine spectra and also DR, DNOE, DEPT, COLOC and 2D‐HSC measurements.
13C and 15N NMR study of mesoionic type A and type B tetrazoles with four nitrogen atoms in the exocyclic group
Authors: Koźmiński Wiktor , Jaźwiński Jarosaw , Stefaniak Lech , Webb Graham A.
Published: May 2005

13C and 15N NMR measurements are reported from a study of five mesoionic compounds containing either the 2,3‐diphenyl‐ or 1,3‐diphenyltetrazolium ring, and either the 2,3‐diphenyltetrazolium ring or its linear analogue as an exocyclic group. Three 15N‐labelled compounds were synthesized for signal assignment purposes. Some 15N13C and 15N15N coupling constants were determined. A proton was found to be located on the exocyclic groups of two of the compounds.
EPR study of Bi‐, Ter‐ and quaterthiophene radical cations
Authors: Kirste Burkhard , Tian Peizhu , Kossmehl Gerhard , Engelmann Gunnar , Jugelt Werner
Published: May 2005

Radical cations of a series of α‐methyl‐substituted bi‐, ter‐ and quaterthiophenes were investigated by EPR and, in part, ENDOR spectroscopy. In the case of terthiophenes, the electronic and steric effects of methyl substituents were studied. The experimentally determined spin density distributions were rationalized by means of semi‐empirical quantum‐mechanical calculations (MNDO, PM3, RHF‐INDO/SP). Sterically non‐hindered oligothiophene radical cations are planar and form mixtures of cis and trans conformers, whereas uniform species were observed in the case of sterically hindered, non‐planar radical cations.
Solid‐state mercury‐199 NMR of hexakis (dimethyl sulphoxidé) mercury (II) trifluoromethanesulphonate: A new standard for mercury‐199 CP/MAS experiments
Authors: Hook James M. , Dean Philip A. W. , van Gorkom Leon C. M.
Published: May 2005

Hexakis(dimethyl sulphoxide)mercury(II) trifluoromethanesulphonate, [Hg(dmso)6](O3SCF3)2, is a stable, readily synthesized compound which is an excellent standard for setting up CP/MAS experiments in solid‐state 199Hg NMR. The isotropic chemical shift, δISO ‐2313 ppm, is to lower frequency than that measured for the same material in solution. The static spectrum exhibits of powder pattern indicative of axial symmetry about the mercury atom, with a chemical shift anisotropy of 122 ppm.
Multinuclear magnetic resonance study of some mesoionic 1,3,4‐triazoles
Authors: Bocian Wojciech , Jaźwiński Jaroslaw , Stefaniak Lech , Webb Graham A.
Published: May 2005

1H, 13C, 14N and 15N NMR data are reported for a series of mesoinoic 1,3,4‐triazoles and some of their salts. The results obtained show that the molecules studied exist in the cyclic mesoionic form with delocalization of the positive charge over the ring atoms. The corresponding negative charge occurs on the atoms of the exocyclic groups, which also act as the site of protonation and salt formation. The most important experimental data for these interpretations are found to be the nitrogen shieldings and that for C‐5.
Pulsed field gradient one‐dimensional NMR selective ROE and TOCSY experiments
Authors: Dalvit Claudio , Bovermann Günter
Published: May 2005

A pulsed field gradient one‐dimensional NMR selective ROE (rotating frame NOE) experiment was designed and successfully tested. The resulting spectra are of high quality and devoid of artefacts. Hence reliable quantification of very weak ROEs necessary for the three‐dimensional structure determination of a molecule is now possible. A similar experiment was designed for the selective 1D TOCSY pulse sequence.
Stereochemistry and synthesis of precursors to strigol analogues
Authors: Tóth Gábor , Halász Judit , Kádas István , Árvai Géza , Mikló Katalin , Haessner Rainer
Published: May 2005

The relative configuration and conformation of the 8‐methyl‐5‐nitro‐1‐oxo‐Δ8(8a)‐octahydronaphthalene isomers were elucidated by various 1H and 13C NMR methods. The structure of the tricyclic by‐products was also determined.
Complete 1H and 13C NMR assignments of two steroid 5, 6β‐epoxides using 1D TOCSY and 2D HMQC TOCSY experiments
Authors: Over Diana E. , Bardet Michel , Marchon Jean‐Claude , Ramasseul René
Published: May 2005

The complete assignments of 1H and 13C data for two steroid epoxides, 3β‐acetoxy‐5,6β‐epoxyandrostan‐17‐one and 3β‐acetoxy‐5,6β‐epoxycholestane, based on DEPT, 1H1H DQF COSY, HMQC, 1D TOCSY and 2D HMQC TOCSY sequences are described. Especially the 1D TOCSY and 2D HMQC TOCSY techniques were essential to the structure elucidation of theses steroids.
17O NMR spectra and conformation of cyclic vinyl ethers
Authors: Taskinen Esko , Ora Mikko
Published: May 2005

The 17O NMR spectra of a number of heterocyclic vinyl ethers were recorded in CDCl3 and DMSO‐d6 solutions. The oxygen chemical shifts reveal substantial differences in the strength of p‐π conjugation between the five‐ and six‐membered ring compounds, especially between those with an exocyclic CC bond. The conformations of the title compounds were estimated by force‐field calculations; the calculated torsional angle of the COCC moiety appears to be a linear function of the 17O NMR shift data, corrected by appropriate structural factors.
Solid‐state 13C NMR spectroscopy. 2‐titanium tetrachloride‐ketone complexes. Structure and mechanism of isomerization
Authors: Maier Günther , Kalinowski Hans‐Otto , Weber Claudia , Henrich Markus
Published: May 2005

The solid‐state 13C NMR spectra of a series of titanium tetrachloride‐ketone and titanium tetrachloride‐ester complexes are presented. The kind of complexation is discussed. The activation energy and the mechanism (planar inversion) for the syn‐anti isomerization at the oxygen atom was evaluated.
13C and 1H NMR assignments for a series of dehydroabietic acid derivatives
Authors: Gigante Bárbara , Santos Lina , Marcelo‐Curto Maria João , Ascenso José
Published: May 2005

Reliable assignments were made for a series of nitro and amine C ring‐substituted dehydroabietic acid derivatives, the main resin acid present in disproportionated rosin and an important intermediate in the chemical industry. A combination of 1D and 2D NMR techniques, including HETCORR, COSY and DEPT experiments, was used. Quaternary carbon atoms, mainly aromatic substituted, require care owing to assignment difficulties that are based on calculated data and are confirmed by long‐range 1H, 13C NMR correlation with selective INEPT and the proton‐detected HMBC experiment.
Theory and application of fully anisotropic overall molecular tumbling, with restricted group internal rotation: 13C NMR relaxation studies of sodium taurocholate and ginsenoside‐Re
Authors: Wang Dehua , Xu Xiaolong , Deng Nianyong , Pen Lianqang , Zhang Wenbin , Stark Ruth E.
Published: May 2005

A theory is presented for fully anisotropic overall molecular tumbling with restricted group internal rotation. This formalism is used with 13C NMR relaxation data and results from molecular mechanics to compute the rotational diffusion rates and methyl group internal rotation rates for sodium taurocholate and ginsenoside‐Re in organic solvents. Although existing theories for steroid derivatives describe methyl internal rotation in terms of free isotropic motion, methyl rotation in ginsenoside‐Re is found to be both sluggish and spatially restricted. The energetic barrier to methyl internal rotation increases significantly with the bulkiness of flexible side‐chains in a series of steroid natural products.
15N NMR studies of guanidines. I—hydrogen bonding and electronic effects in conformationally flexible guanidines
Authors: Bedford Geoffrey R. , Taylor Peter J. , Webb Graham A.
Published: May 2005

Hydrogen bonding and electron distribution in some heterocyclic guanidines were studied by 15N NMR spectroscopy, using other substituted guanidines as points of reference. Solvent effects were used to distinguish the 15N NMR signals for their two sp2 nitrogen atoms, since ring nitrogen forms an intramolecular hydrogen bond and so is much less sensitive to solvent than is the guanidine unit. The effect of substituent is discussed in terms of competition between through‐resonance and the more localized resonance of the π‐inductive effect. These are favoured, respectively, by oxygen (nitro, acyl) and nitrogen (cyano) acceptor groups, whereas heterocycles, also nitrogen acceptors, occupy an intermediate position. Among the latter class, there are indications that the balance between these forms of resonance may be influenced by competitive conjugation with ring π‐donor heteroatoms.
15N NMR studies of guanidines. II—the fused‐in guanidine unit of some oxoheterocycles: A combined 15N NMR, 13C NMR and IR study
Authors: Bedford Geoffrey R. , Taylor Peter J. , Webb Graham A.
Published: May 2005

15N NMR spectroscopy was used to extend previous studies, by 13C NMR and IR spectroscopy, of fused oxoheterocycles which contain the guanidine unit. These compounds fall into three clearly definable structural types, through‐conjugated, ring‐conjugated or imide‐like, any or all of which may result from the cyclization reactions used for their synthesis. It is shown that 15N NMR and IR criteria are of equal value in distinguishing these, whereas 13C NMR is in general unhelpful. A qualitative correlation exists between v(CN) for the guanidine unit, and the summed 15N NMR chemical shifts for the two π‐donor nitrogen atoms. The present observations should help to establish spectroscopic criteria for structural elucidation.
Neutral hyperconjugation challenged: No support from one‐bond CC coupling constants
Authors: Kamieńska‐Trela Krystyna
Published: May 2005

A significant decrease in 1J(Cipso, CH2) coupling constants from a value typical of C(sp2)C(sp3) bonds (43.5 Hz or smaller) to the unexpectedly low value of 36 Hz typical of C(sp3)C(sp3) bonds was reported by Lambert and Singer on passing from XC6H4CH2Sn(CH3)3 to XC6H4CH2C(CH3)3 (X = H, CH3, OCH3, NO2). This trend was invoked by these authors as the first evidence for neutral hyperconjugation in terms of coupling constants. However, the present measurements reveal that also in C6H5CH2C(CH3)3 and p‐O2NC6H4CH2C(CH3)3 the 1J(Cipso, CH2) coupling constant bears a value typical of this type of bonding (43.8 and 42.6 Hz, respectively). Thus, at variance with Lambert and Singer's observation, a slight increase in 1J(CC) coupling constants occurs on passing from Sn to C derivatives. This contradicts not only their experimental data but also conclusions concerning hyperconjugation in the neutral ground state.
Total assignment of the 1H and 13C NMR chemical shifts of four bufadienolides by 2D NMR spectroscopy
Authors: Reynolds William F. , Maxwell Anderson , Telang Balchandur , Bedaisie Kishore , Ramcharan Gangadeen
Published: May 2005

Four known bufadienolides, marinobufagin (1), telocinobufagin (2), bufalin (3) and resibufogenin (4), were isolated from the toad Bufo marinus. The 1H and 13C NMR spectra were completely assigned by using a combination of 13C DEPT and 2D NMR experiments (1H1H COSY, HMQC, HMBC and NOESY). The full 1H NMR data for 1–4 and 1H and 13C NMR data for 2 are reported for the first time.
Multinuclear magnetic resonance study of N,N′,N″‐tris(trimethylsilyl)borazine
Authors: Wrackmeyer Bernd , Schwarze Bernd , Durran D. Michael , Webb Graham A.
Published: May 2005

The nuclear spin relaxation rate of the quadrupolar 14N nuclei in N,N′,N″‐tris(trimethylsilyl)borazine (1) is surprisingly slow [T1(14N)=0.1 s]. This allows one to measure 1J(29Si14N) (9.6 Hz) directly from the 29Si NMR spectra and also to compare signs of coupling constants 1J(29Si14N) (<0) and 3J(14NSiC1H) (>0) by 2D 29Si/1H HETCOR experiments. Since the transverse relaxation time T2(14N) in 1 is governed by scalar relaxation of the second kind, the magnitude of 1J(14N11B) can be evaluated (23 ± 0.5 Hz). 11B, 14N and 29Si NMR data for N,N′‐bis(trimethylsilyl)borazine (2) were also obtained, and 11B and 14N NMR spectra of the parent borazine [HBNH]3 (3), and of [HBNMe]3 (4) were remeasured. Calculation of the tensor components of the 14N electric field gradient shows that eqzz in 1 and in 2 for 14N(Si) is significantly smaller than for other borazines [HBNR]3, e.g. with R=H (3) or Me (4), in agreement with the experimental results.
A 1D H, C correlation with homonuclear cross‐polarization
Authors: Zangger Klaus , Sterk Heinz
Published: May 2005

A 1D H, C correlation ROESY experiment is suggested and applications for signal assignments via through‐bond and through‐space correlations are demonstrated using glutathione and 1‐O‐methyl‐4,6‐O‐benzylidene‐α‐D‐glucopyranoside.
Intramolecular hydrogen bonding and conformation of a dipyrrolic derivative
Authors: Díaz E. , Galeazzi E. , Nava J. L. , Muchowski J. M. , Guzmán A. , van Calsteren M. R. , Jankowski K.
Published: May 2005

The conformation of 1‐phenyl‐1‐(1,2‐dimethyl‐5‐pyrrolyl)‐2‐(2‐methyl‐5‐benzoyl‐1‐pyrroly)ethanol, with characteristics of a molecular propeller, is stabilized by intramolecular hydrogen bonding as detected by 1H NMR, NOE difference experiments, 2D NMR, COSY, 13C NMR, HETCOR, HMBC and 1H NMR variable‐temperature experiments.
Magnetization transfer NMR study of nitrogen inversion in 2,2‐dimethylaziridine
Authors: Johnston Eric R.
Published: May 2005

The slow inversion at pyramidal nitrogen in 2,2‐dimethylaziridine was investigated by NMR spectroscopy at 304 K using one‐dimensional spin locking methods and two‐dimensional exchange spectroscopy. The activation free energy was found to be 17.5 kcal mol−1 (73.2 kJ mol−1) at this temperature. This value represents a lower limit for the unimolecular inversion barrier height as autocatalytic and water‐catalyzed inversion pathways can in principle also contribute to the observed rate. The spin locking experiments described employ non‐selective pulses and are particularly useful for the quantitative study of slow chemical exchange between nuclei of similar resonance frequency where selective magnetization transfer experiments are difficult or impossible.
Distinguishing two‐bond and three‐bond 13C1H connectivities by 2D BIRD‐decoupled difference spectra: The DODO pulse
Authors: Reynolds William F. , Yang Ji‐Ping , Enriquez Raul G.
Published: May 2005

A modified BIRD pulse, called the DODO pulse, was developed and incorporated into one version of the FLOCK sequence. Addition of the two‐dimensional spectra obtained with this modified sequence and with the unmodified FLOCK sequence produces a normal indirectly bonded 13C1H shift correlation spectrum. Subtraction of one spectrum from the other generates a difference spectrum which allows a clear distinction between two‐bond and three‐bond 13C1H connectivities among protonated carbons.
Investigation of structural inhomogeneities in soft‐block modified methacrylate resins
Authors: Clayden Nigel J. , Smyth Gerard
Published: May 2005

Wideline 1H NMR and selective high‐resolution 13C cross‐polarization magic angle spinning (CP/MAS) NMR spectroscopy was used to investigate the polymer structure in methacrylate thermoset resins modified by the incorporation of a polyether soft‐block. Spin diffusion experiments indicate phase separation between a hard‐ and soft‐block phase. Similar soft‐block domain sizes were found regardless of the soft‐block content, reflecting the discriminatory nature of the delay used to create the magnetisation gradient. The main effect of increasing the polyether content is to ensure that more of the sample adopts a two‐phase hard/soft morphology. The selective 13C CP/MAS NMR spectra show that partial mixing of the methacrylate resin and polyether must occur and adding a Goldman‐Shen preparation period establishes that the mixing occurs through the bulk and is not simply interfacial.
2,5‐dihydro‐1,2,5‐azasilaborole derivatives studied by 15N and 29Si NMR using Hahn‐echo and pseudo‐BIRD experiments
Authors: Wrackmeyer Bernd , Kupče ĒRiks , Köster Roland , Seidel Günter
Published: May 2005

15N and 29Si NMR data of 2,5‐hydro‐1,2,5‐azasilaborole derivatives and related compounds were determined with emphasis on coupling constants 1J(29Si 15N) which cannot be measured from 15N NMR spectra of most boron‐nitrogen compounds. In the case of compounds with an SiNH fragment ψ‐Bird pulse sequences, combined with HMQC or HSQC, served for 1H detection of the 29Si resonance with preselection of the 15N‐1H spin pair. This permitted the measurement of 1J(29Si 15N) and the determination of its absolute sign (>0). In the absence of an NH group, the coupling constants 1J(29Si 15N) were measured from the 15N satellites in 29Si NMR spectra recorded by using the Hahn‐echo extended (HEED) refocused INEPT pulse sequence. Isotope induced chemical shifts 1Δ 15/14N(29Si) were also measured by this technique for all the compounds. The 1J(29Si 15N) values cover the range 8.4–17.0 Hz, depending on the substituents at boron, silicon and nitrogen and on the complexation of the heterocycle.
The 15N‐isotopomers of cis‐ and trans‐difluorodiazine; A 19F NMR investigation of the two [AX]2 spin systems of 15N2F2
Authors: Aubke F. , Hägele G. , Willner H.
Published: May 2005

The decomposition of 15N3F at −20°C leads to cis‐ and trans‐15N2F2. The corresponding 19F NMR spectra were analysed as [AX]2 systems. 19F, 15N and 14N NMR spectra were simulated using the novel PC program systems DSYMPCD, DCYMPCD and WIN‐DAISY running under WIN‐NMR. Stereospecific coupling constants were obtained for both isomers. Comparison of the 19F NMR spectra from both the [1/2A1/2X]2 and the [1A1/2X]2 systems in 15N2F2 and 14N2F2 overcomes the inherent ambiguities of the [AX]2 analysis.
Highly selective 1D CH correlations
Authors: Stelten Johannes , Leibfritz Dieter
Published: May 2005

Semi‐selective 1D one‐bond 1JCH correlations with 13C or 1H detection and multiple‐bond nJCH correlations with 1H detection are described. In these methods INEPT is used for the polarization transfer and pulsed field gradient coherence transfer pathway selection. The pulse sequences are designed particularly with regard to solving efficiently sterochemical problems in organic molecules with minimum acquisition time. The methods also allow easy quantification of heteronuclear nJCH coupling constants.
Separation and characterization of components of peptide libraries using on‐flow coupled HPLC—NMR spectroscopy
Authors: Lindon J. C. , Farrant R. D. , Sanderson P. N. , Doyle P. M. , Gough S. L. , Spraul M. , Hofmann M. , Nicholson J. K.
Published: May 2005

The efficiency of directly coupled HPLC—NMR spectroscopy for the separation and characterization of synthetic peptide libraries was investigated using a model system based on a mixture of all 27 tripeptide combinations of alanine (A), methionine (M) and tyrosine (Y) as the C‐terminal amides. The 1H NMR spectra were obtained in real time using on‐flow HPLC—NMR spectroscopy at 600 MHz and 21 of the 27 peptides were identified on the basis of chemical shifts and coupling constants, including the use of diagnostic values derived from 1H NMR spectra and 1H13C and 1H15N HMQC studies on authentic AAAOH and YYYOH. The effects on 1H NMR chemical shifts of pH and of varying proportions of acetonitrile and water as occurred during the gradient elution HPLC run were evaluated. The HPLC—NMR approach could provide a facile method for investigating the relative efficiency of resin‐based peptide synthesis for different amino acid combinations and should rapidly provide data suitable for deriving structure‐retention time relationships for peptides.
Structural assignment of the intramolecular meta photocycloadduct isomers from 4‐phenoxybut‐1‐enes and 3‐benzyloxyprop‐1‐enes by proton NMR spectroscopy
Authors: Blakemore D. C. , Gilbert A. , De Bruyn A. , De Keukeleire D. , Van der Eycken E.
Published: May 2005

1H NMR data (400 and 500 MHz) are reported for the intramolecular meta photocycloaddition products from 4‐phenoxybut‐1‐enes and 3‐benzyloxyprop‐1‐enes. The structures of these photoproducts, and in particular the discrimination between the 1,6‐ and 7,8‐bridged isomers, are deduced from COSY 45 and 60 experiments and spin‐decoupling techniques.
13C NMR study of some sulphur‐containing 5‐trifluoromethylpolychloro‐pyridines
Authors: Sveshnikov Nikolay N. , Sipyagin Alexey M. , Dobrokhotova Olga V.
Published: May 2005

A 13C NMR study of a series of novel 2,4‐thio‐substituted 5‐trifluoromethylpoly‐chloropyridines was carried out. The carbon chemical shifts and external long‐range 13C, 19F NMR coupling constants between the pyridine ring carbons and the trifluoromethyl group are reported.
Héterocycles contenant du phosphore—XVII: Etude par Résonance Magnétique Nucléaire et analyse conformationnelle de quelques oxazaphosphorinanes‐1,3,2
Authors: Durrieu Josiane , Kraemer Raymond , Navech Jacques
Published: May 2005

Le spectre de RMP de quelques nouveaux oxazaphosphorinanes‐1,3,2 est analysé. Dans un cas, après élimination du couplage entre les protons et le phosphore, on a affaire à un système ABKLXY particulier dans lequel certaines constantes de couplage entre protons vicinaux sont nulles. Le système ABKLXY où JAK = JAL = JBK = JBL est étudié, ce qui permet d'accéder à la plupart des paramètres du composé considéré. La conformation du cycle est précisée, la valeur de l'enthalpie libre conformationnelle est donnée et, pour l'oxazaphosphorinane‐1,3,2 précédent, l'angle de torsion des liaisons C4C5 et C5C6 est calculé.
NMR studies on the interaction of methylaluminium compounds with some methyl‐substituted pyridines
Authors: Wakatsuki Kizuku , Matsubayashi Gen‐etsu , Tanaka Toshio
Published: May 2005

The interactions of trimethylaluminium and dimethylaluminium chloride with some methyl‐substituted pyridines have been investigated in dichloromethane by means of temperature‐dependent proton NMR spectra. 4‐Methylpyridine forms 1:1 addition complexes with trimethylaluminium and dimethylaluminium chloride. 2,6‐Dimethyl‐ and 2,4,6‐trimethylpyridines have been found to yield three types of complex with dimethylaluminium chloride, however, and only one type of complex with trimethylaluminium. The configurations of the complexes in solution, and exchange equilibria between methylaluminium compounds and 2,6‐dimethylpyridine are also discussed.
An indo investigation of magnetic resonance constants of azaaromatic systems
Authors: Galasso V.
Published: May 2005

INDO–MO calculations have been performed on the ESR hyperfine coupling constants of the pyridinyl radical and the radical anions of pyrimidine, quinoline, isoquinoline, acridine and benzcinnoline. The nuclear spin coupling constants and the 14N nuclear quadrupole coupling constant of pyridine have also been calculated. In general, calculated values are in satisfactory agreement with the experimental data.
Ionen. X—Das Tetraphenyloborat‐Ion als Hilfsmittel bei Diastereotopie‐Problemen
Authors: Schiemenz G. P. , Klemm P.
Published: May 2005

[B(C6H5)4]⊖ ist ein leistungsfähiges NMR‐Verschiebungsreagens für Aminosulfonium‐Kationen. In einem Beispiel zeigen diastereotope Protonen unter normalen Meßbedingungen (Chlorid in CDCl3) keine Anisochronie. Diese wird durch einen Solvenseffekt sichtbar, jedoch nur in einem Maße, das die geminale Kopplungskonstante und die wahren Signallagen noch nicht zu ermitteln gestattet. [B(C6H5)4]⊖ erzeugt jedoch annähernd ein Spektrum erster Ordnung, dem alle Parameter glatt entnommen werden können. Die Daten helfen im Chlorid‐Spektrum sehr schwache Signale aufzuspüren und das Ausmaß der Anisochronie festzustellen. Salzmischungen legen verdeckte Signale frei.
Carbon‐13 nuclear magnetic resonance spectroscopy: VIII—aliphatic hydrocarbon derivatives
Authors: Miyajima Goh , Nishimoto Kichisuke
Published: May 2005

Carbon‐13 NMR chemical shifts of several series of aliphatic hydrocarbon derivatives–‐substituted methanes, ethanes, isopropanes, n‐propanes and n‐butanes–‐were found to have a linear relationship with σ‐electron densities (Qσ) calculated by the method of σ‐included ω‐HMO. A plot of the 13C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in a substituted butane showed a good linearity with a slope of unity. The values of the 13C chemical shifts of the n‐butyl derivatives converged rapidly to a constant value as the distance from the substituent increased. Accordingly, the value for the δ‐carbon was found to be constant regardless of the substituent. These results show that the 13C NMR chemical shifts of aliphatic hydrocarbon derivatives are mainly dependent on inductive effects. The convergence shown by the experimental results is supported by the calculated results of the Qσ values of the n‐butyl derivatives.
Calculation of gauche coupling constants from substituent electronegativities
Authors: Forrest T. P.
Published: May 2005

The calculation of gauche coupling constants from substituent electronegativities by a method which takes into account the orientation of the substituents is described. This correlation has been derived from the coupling constants of disubstituted ethanes and has been applied to the calculation of coupling constants in cyclohexanes and 6‐membered heterocycles. The detection of angular distortion in 6‐membered rings from the difference between calculated and observed coupling constants is also described.
The 19F NMR spectrum of cis‐1,2‐dichlorohexafluorocyclobutane
Authors: Gazzard Valerie J. , Harris Robin K.
Published: May 2005

The 19F spectrum of cis‐1,2‐dichlorohexafluorocyclobutane has been fully analysed on the basis of an [ABX]2 spin system, with initial treatment at an [AMX]2 level. The chemical shift and coupling constants are presented, and the latter are discussed. Some comments are made on the spectrum of the trans isomer.
Mise en evidence de plusieurs processus d'échange intramoléculaire dans les iodures de bis(méthyl thio)‐1,1 dialkyl iminio‐3 propène substitués ou non en 2 et 3
Authors: le Botlan Denis , Filleux‐Blanchard Marie‐Louise , le Coustumer Gérard , Mollier Yves
Published: May 2005

Une étude RMN des sels d'iminium de formule générale a été réalisée à diverses températures.
13C FT‐NMR spectra of alkyl substituted furans. A study of the influence of steric interactions
Authors: Kiewiet A. , de Wit J. , Weringa W. D.
Published: May 2005

The 13C FT‐NMR spectra of thirteen furans, monodi‐ or trisubstituted with methyl and/or t‐butyl groups, were studied in detail. Substituent effects of methyl and t‐butyl groups on the chemical shifts of ring carbon atoms are additive in nonsterically hindered furans. Steric shifts for the ring carbon atoms are found in furans with bulky neighbouring substituents, but the hybridisation of the carbon atoms in these hindered furans is not changed. The chemical shifts of the substituents are calculated according to the Grant‐Cheney formula. No simple relationship between steric shift and steric hindrance can be ascertained.
Conformational studies by nuclear magnetic resonance. VII—The direct observation of rotational isomers in some enamino carbonyl compounds and their thione derivatives by carbon magnetic resonance
Authors: Da̧browski Janusz , Kamieńska‐Trela Krystyna , Kozerski Lech
Published: May 2005

Carbon‐13 magnetic resonance spectra of the s‐cis and s‐trans rotamers of enamino ketones and thiones of the general formula
\documentclass{article}\pagestyle{empty}\begin{document}${\rm X =}\mathop {\rm C}\limits^{\rm 1} {\rm (}\mathop {\rm R}\limits^{\rm 1} {\rm)}\mathop {\rm C}\limits^{\rm 2} {\rm H =}\mathop {\rm C}\limits^{\rm 3} {\rm HN}\mathop {{\rm R}_{\rm 2}}\limits^{\rm 4}$\end{document} (where × = O or S and R‐1, R‐4 = alkyl) have been obtained. With dimethylaminoacrolein and its thione analogue, restricted rotation could only be observed in the latter. The chemical shift differences between rotamers and homologues are attributed to changes in conjugation and to induced bond polarisation, both these factors resulting from steric strain. In particular, nonplanar deformations of the s‐trans rotamers are deduced from their C‐2 chemical shift values.
Photodimers of cinnamic acid and related compounds. A stereochemical study by NMR
Authors: Montaudo G. , Caccamese S. , Librando V.
Published: May 2005

1H NMR spectra of photodimers of cinnamic acid, chalcone and related compounds were analysed, and the spectral parameters and all the coupling constants were obtained. A clear differentiation among the head‐to‐head and head‐to‐tail stereoisomers can be obtained by considering the values of K, L, M and N parameters. The different types of hh and ht isomers can be immediately assigned by considering the relative values of the three‐bond couplings. An authentic example of an A2B2 spin system is reported.
Carbon‐13 spin‐lattice relaxation times and nuclear overhauser enhancements in some simple fluorocarbons
Authors: Hawkes Geoffrey E. , Abraham Raymond J.
Published: May 2005

Carbon‐13 spin‐lattice relaxation times (T1) and 13C‐{19F} nuclear Overhauser enhancement (NOE) factors have been measured for some simple fluorocarbons by pulse‐Fourier transform methods—‘progressive saturation’ and ‘dynamic Overhauser enhancement’. The NOE factors are shown to be large for 13C with directly bonded fluorines, and the values for T1 and the NOE factors are similar to those obtained elsewhere on the corresponding hydrocarbons.
Evidence from fluorine and proton NMR spectra for restricted rotation about the PO bond in some steroidal phosphorofluoridates
Authors: Cooper G. H. , Chittenden Rosemary A.
Published: May 2005

The salient features of the 19F and 1H NMR spectra of seven steroidal phosphorofluoridates are presented and evidence for restricted rotation, obtained from high temperature studies and deuteration experiments, is discussed.
The proton exchange reaction between indene and the indenyl anion
Authors: Vos H. W. , Bakker Y. W. , Velthorst N. H. , Maclean C.
Published: May 2005

The proton exchange reaction between the indenyl carbanion and its parent compound indene has been studied by NMR as a function of temperature. The rate of this bimolecular reaction is very low and has been found to be strongly dependent on the polarity of the solvent. In solvents like dimethoxyethane (ϵ = 7·2) and diglyme the reaction becomes manifest in the NMR spectrum only at elevated temperatures (T > 150°C). In hexamethylphosphortriamide (ϵ = 30) the rate is much greater and line broadening may be observable at room temperature. The reaction in this solvent is characterised by a frequency factor f = 7 × 107 1 mol−1 s−1, an activation enthalpy ΔH ≠ = 9·5 kcal mol−1 and an entropy of activation ΔS≠ = −23 e.u. The low reaction rate and its solvent dependence are briefly discussed.
Analysis of the 1H NMR spectrum of α‐tetralone
Authors: Gatto Karen , Reinheimer John D. , Shafer Kenneth , Gerig J. T.
Published: May 2005

An analysis of both the aromatic and aliphatic portions of the 1H NMR spectrum of α‐tetralone has been carried out. Two deuterated derivatives, 2,2‐dideuterio‐ and 4,4‐dideuterio‐α‐tetralone, were prepared to facilitate unambiguous assignment of chemical shifts for the aliphatic protons. The conformation of the 6‐membered alicyclic ring of the molecule is defined by the coupling constants among the aliphatic protons. Benzylic coupling was the only detectable long range interaction between the aliphatic and aromatic protons of the molecule. The magnitude and sign of these coupling constants agree with previous calculations of Wasylishen and Schaefer.
A carbon‐13 NMR study of some sulfur‐containing organic compounds
Authors: DeSimone Richard E. , Albright Michael J. , Kennedy William J. , Ochrymowycz Leo A.
Published: May 2005

Carbon‐13 NMR spectra have been obtained and analyzed for a series of saturated linear and cyclic sulfur‐containing organic molecules. For the large cyclic polythiaethers whose proton spectra are broad and unresolved, it is found that carbon‐13 spectra are sharp and well resolved. The resonances of all carbons fall within the expected chemical shift ranges. Based upon the comparative resolution in the spectra of large and small cyclic species, it is concluded that whatever conformational motion may exist within the rings must be occurring very rapidly on the NMR time scale.
The determination of conformational effects in some fluorobenzenes by a combined mo/coupling constant treatment
Authors: Abraham Raymond J. , Busby James F. , Cooper M. Ashley , Roe Anthony M.
Published: May 2005

The correlation of JmetaFF in some 1‐substituted‐2,6‐difluorobenzenes (1) with the bond order matrix of the fluorine 2p(π) orbitals provides information on the orientation of the substituents and the position of the counter‐ion in the anilinium salt. The calculated charge densities in the analogous anilinium fluoride ion pair are compared with those of the free ion and neutral molecule.
13C NMR studies: XLVI—rearrangements and deuterium exchange via homoenolization in bicyclooctanones. A convenient preparation of bicyclic β,γ‐ and γ,δ‐unsaturated ketones
Authors: Hudyma D. M. , Stothers J. B. , Tan C. T.
Published: May 2005

With t‐BuO−/t‐BuOH at 185°C bicyclo‐[2.2.2] and ‐[3.2.1]octanones are interconvertible. In saturated systems equilibrium is attained very slowly, but in unsaturated cases an equilibrium mixture heavily favoring the [3.2.1] skeleton is obtained relatively rapidly, thereby providing a convenient route to homo and bis‐homo conjugated ketones. Experiments in t‐BuOD using 13C NMR to monitor deuterium incorporation revealed five major sites of exchange in the unsaturated ketones.
13C13C coupling constants and substituent effects on 13C chemical shifts in 13C labelled pyrene and pyrene derivatives
Authors: Hansen P. E. , Poulsen O. K. , Berg A.
Published: May 2005

Long range inter‐ring 13C13C couplings are found to be effective in the title compounds, and the magnitudes of coupling constants and of substituent effects on 13C chemical shifts, as well as the signs of the latter, alternate with respect to the number of connecting bonds.
Hindered rotation of the dimethylamino and dimethylthioamide groups in two ortho substituted N,N‐dimethylthiobenzamides
Authors: Lozac'h R. , Legrand L. , Sandström J.
Published: May 2005

Hindered rotation in two o‐substituted N,N‐dimethylthiobenzamides was investigated by variable temperature 1H NMR spectroscopy. For one compound, the enthalpies and entropies of activation for (i) thioamide group rotation around the ArC bond and (ii) dimethylamino group rotation around the CN bond were obtained by full line shape analysis; a possible coupling between the two processes is discussed. A new simple method has also been applied to the analysis of dimethylamino exchange and results are in complete agreement with the full line shape analysis with somewhat better precision.
NMR studies on σ‐adducts of heterocyclic systems with nucleophiles. VI—Carbon‐13 nuclear magnetic resonance investigations on σ‐adduct formation of pyrimidine and some of its derivatives with potassium amide in liquid ammonia
Authors: Geerts J. P. , van der Plas H. C. , van Veldhuizen A.
Published: May 2005

Carbon‐13 NMR spectra of the σ‐adduct complexes formed in liquid ammonia between the amide ion and some 2‐R‐pyrimidines, some 4‐chloro‐2‐R‐pyrimidines (R = dimethylamino‐, N‐methylanilino, piperidino‐, morpholino‐, phenyl‐), 5‐bromo‐2‐piperidinopyrimidine and pyrimidine itself are described, together with the carbon‐13 NMR spectra of the anions formed by amino‐proton abstraction resulting from the reaction of the amide ion with 2‐anilino‐4‐chloro‐, 4‐chloro‐2‐methylamino‐, 2‐anilino‐ and 2‐methylaminopyrimidine in liquid ammonia. Additionally, the carbon‐13 NMR spectra of the parent compounds of the anionic σ‐adducts and anions, and that of 4‐chloropyrimidine, were recorded in CDCl3.
Mutual assignment of subspectra and substructures—A way to structure elucidation by 13C NMR spectroscopy
Authors: Bremser W. , Klier M. , Meyer E.
Published: May 2005

A novel approach to utilising digital computers and a collection of reference data for the interpretation of 13CNMR spectra is outlined. Because of the almost unlimited possibilities of molecular structures in organic chemistry, a matching of subspectra with substructures seems most appropriate, followed by an iterative confirmation of the suggested structures. For this purpose the possibility of a search for structure increments and the accompanying chemical shifts is provided by linking the spectroscopic and structural information using a formulae reading machine and generating the topological connectivity table. Three practical examples demonstrate the application of this set of programs and some of the experiences gained during operation.
Mechanism of serine protease action. Ionization behavior of tetrahedral adduct between α‐lytic protease and tripeptide aldehyde studied by carbon‐13 magnetic resonance
Authors: Hunkapiller Michael W. , Smallcombe Stephen H. , Richards John H.
Published: May 2005

Magnetic resonance techniques have been used to study the ionization behavior of the catalytic triad of the serine protease, α‐lytic protease, in the tetrahedral, hemiacetal complex it forms with the aldehyde inhibitor, N‐ac‐L‐ala‐L‐pro‐L‐alaninal. Chemical shift, coupling constant and relaxation measurements of a carbon‐13 nucleus specifically incorporated in C‐2 of the imidazole ring of the single histidine residue of the protein show that, above pH 7, the imidazole ring of the catalytic triad in the enzyme + aldehyde complex is neutral. We suggest, further, that a neutral carboxylic acid group for Asp 102 and an oxyanion for the hemiacetal are most likely to describe the state of ionization of the other groups above pH 7. Around pH 6·25, both the oxyanion and the histidine become protonated in a co‐operative process which forces the histidine away from its rigidly localized position as a member of the catalytic triad into a solution‐like environment.
13C‐NMR‐Spektroskopie von Cyclopropenonen und Cyclopropenyliumionen (Cyclopropenonchemie: VII)
Authors: Dehmlow Eckehard V. , Zeisberg Reinhard , Dehmlow Sigrid S.
Published: May 2005

Die 13C‐NMR‐Spektren von dreizehn Cyclopropenonen, zwei Cyclopropenthionen, fünf zugehöriger Cyclopropenyliumsalze und von drei Cyclobutendionen werden tabelliert und diskutiert.
Silicon‐29 and carbon‐13 NMR studies of organosilicon chemistry. II—The Methylethoxysilanes MenSi(OEt)4−n
Authors: Harris Robin K. , Kimber Barry J.
Published: May 2005

Silicon‐29, carbon‐13 and oxygen‐17 NMR data are reported for the methylethoxysilanes, MenSi(OEt)4−n with n = C to 3. The values of 1J(SiC) vary greatly, in a manner which appears to be inconsistent with an effect of s‐character variation alone. The chemical shifts are discussed in terms of possible π‐bonding. Silicon‐29 and carbon‐13 spin‐lattice relaxation times and nuclear Overhauser effects are also reported and discussed.
Carbon‐13 NMR spectra of all‐trans‐N‐retinylidene‐n‐butylamine as an analogue of the Schiff's base linkage‐compound in visual pigment
Authors: Tokitô Yasuo , Inoue Yoshio , Chûjô Riichirô , Miyoshi Yasuhiro
Published: May 2005

Carbon‐13 NMR spectra have been obtained for all‐trans‐N‐retinylidene‐n‐butylamine as an analogue of the Schiff's base linkage compound in visual pigment. The chemical shift changes on going from all‐trans‐retinal1 to all‐trans‐N‐retinylidene‐n‐butylamine are observed. These changes indicate the collapse of the bond alternation in conjugated polyene carbons, whereas N‐protonation in all‐trans‐N‐retinylidene‐n‐butylamine does not affect the bond alternation.
Carbon‐13 NMR spectroscopy of the biological pigments luteoskyrin and rugulosin and some polyhydroxyanthraquinone analogues
Authors: Toma F. , Bouhet J. C. , Van Choung P. Pham , Fromageot P. , Haar W. , Rüterjans H. , Maurer W.
Published: May 2005

The bianthraquinonic biological pigments luteoskyrin and rugulosin and five polyhydroxyanthraquinone derivatives are studied by carbon‐13 NMR in DMSO solution. Peak assignment for the fourteen carbon atoms of these compounds is achieved by proton spin decoupling and by investigating the effect of ionisation of the hydroxyl groups upon the carbon chemical shifts. Carbon chemical shifts in the planar hydroxyanthraquinones can be rationalised in terms of conjugation and intramolecular hydrogen bonding. The latter is responsible for the relative acidity of the hydroxyl groups in the analogues, and for the different conformations proposed for luteoskyrin and rugulosin. Tautomeric equilibria occur in DMSO and water–DMSO solutions for the anionic species [LS]2− and [RG]2−. This can account for the binding of luteoskyrin and rugulosin to nucleic acids.
RMN du carbone‐13 en serie cyclopropanique. Effets de substituants
Authors: Monti J. P. , Faure R. , Vincent E. J.
Published: May 2005

Les effets de substituants sur les déplacements chimiques de dérivés cyclopropaniques ont été étudiés par RMN du carbone‐13. Les déplacements chimiques théoriques de cyclopropanes trisubstitués sont en bon accord avec les valeurs expérimentales lorsqu'on introduit dans les corrélations des paramètres d'interaction du second ordre.
The structure of pyrazine determined from its proton magnetic resonance spectrum, including the carbon‐13 satellites
Authors: Diehl P. , Bösiger H. , Tracey A. S. , Ader R.
Published: May 2005

The structure of pyrazine partially oriented in a liquid crystal has been determined from its proton magnetic resonance spectrum utilising the 13C satellites (at natural abundance). Carbon–carbon, carbon‐hydrogen and hydrogen–hydrogen internuclear distance ratios have been determined.
1H and 31P NMR spectra of substituted methylphosphonic acids with indirect determination of 31P shifts
Authors: Rueppel M. L. , Marvel J. T.
Published: May 2005

Proton and phosphorus magnetic resonance spectra of substituted methylphosphonic acids have been determined as a function of pH. A method has been developed for measuring the 31P shift indirectly by optimal heteronuclear decoupling of the 1H spectra of samples and standards. Control experiments have demonstrated the broad applicability of this technique to the characterization of low milligram samples of N‐phosphonomethylglycine and potential metabolites.
Quantitative analysis by nuclear magnetic resonance with fourier transform II13C resonance
Authors: Thiault B. , Mersseman M.
Published: May 2005

Quantitative analyses have been carried out by 13C NMR spectroscopy using Fourier transformation. The Overhauser effect, due to the broad band decoupling of protons, has been suppressed using the two existing methods (gated decoupling and paramagnetic species), and results from each are compared. Both require a calibration curve, and the second method, when applied to aromatic substances, needs the ratio between the sample to be analysed and the paramagnetic species to be less than a certain value. Experiments have been made with pure products and blends of pure products containing both saturated and aromatic carbons. The precision of the results is given.
The 1H NMR spectra of zinc complexes of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone
Authors: Bell C. F. , Mortimore G. R. , Reed G. L.
Published: May 2005

Proton magnetic resonance spectra at 100 MHz are described for some zinc complexes of the E‐ and Z‐isomers of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone in d6‐dimethylsulphoxide solution. Chemical shift data are discussed qualitatively in relation to factors such as the charge on the metal ion, the anisotropy of ligand nitrogen atoms, electric field effects caused by the dipole moment of nitrogen lone pairs, metal‐nonbonded‐hydrogen interactions, ring current effects and the conformational changes undergone by each isomer on coordination.
13C NMR of organosulphur compounds: I—the effects of sulphur substituents on the 13C chemical shifts of alkyl chains and of S‐heterocycles
Authors: Barbarella Giovanna , Dembech Pasquale , Garbesi Anna , Fava Antonino
Published: May 2005

The 13C NMR spectra have been determined of: (i) aliphatic compounds having at one end a functionalized sulphur atom (SH, S−, SMe, S(O)Me, SO2Me and S+Me2) and (ii) saturated sulphur heterocycles variously substituted at the S‐atom . The results are discussed in terms of the familiar deshielding effects for α‐ and β‐carbons and shielding effects for γ‐carbons, exerted by the sulphur atom itself and/or by the atoms or groups of which the sulphur function is made up. The γ‐effect of the S‐atom appears to be nearly independent of the nature of the S‐function and of comparable magnitude to that of an aliphatic carbon (−2·5 + −3·0 ppm). Surprisingly, however, a SCH3 group shields the carbon in γ position with respect to CH3 by an amount (−5·4 ppm) which is more than twice that (−2·5 ppm) exerted by the aliphatic γ‐carbon on the S‐CH3 carbon itself. As to the cyclic compounds, the shieldings of the α‐ and β‐carbons can be rationalized in terms of the conformational orientation of the substituent at sulphur, and the equilibrium distribution of the conformers. The results confirm the great value of 13C NMR for configurational and conformational assignment of S‐heterocycles.
13C NMR spectroscopy of polycyclic aromatics. VIII—amino derivatives of quinoline, isoquinoline, acenaphthene and fluoranthene
Authors: Ernst Ludger
Published: May 2005

Complete assignments of the 13C n.m.r. spectra have been made for 5‐aminoquinoline, 5‐aminoisoquinoline, 5‐aminoacenaphthene and 3‐aminofluoranthene. Substituent‐induced shifts are compared with those of the structurally related 1‐aminonaphthalene. Some deviations within the series can be interpreted in terms of an increase of the exocyclic peri angle. An analysis of the 1H n.m.r. spectrum of 3‐aminofluoranthene is also given.
13C NMR spectra of some N‐aryl substituted sulphur–nitrogen compounds
Authors: Kresze G. , Berger M. , Claus P. K. , Rieder W.
Published: May 2005

The 13C n.m.r. spectra of four classes of N‐aryl sulphur–nitrogen compounds are discussed. The para carbon shieldings of the N‐phenyl derivatives reflect the substituents effects of the various nitrogen groups. These show large differences for the four classes of compounds due to differences in the electronic structure of the sulphur–nitrogen bond.