bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon‐13 NMR relaxation studies of some dicyclohexyl compounds at high pressure
Authors: Gillies Duncan G. , Matthews Stephen J. , Sutcliffe Leslie H.
Published: May 2005

Four dicyclohexyl compounds were investigated, one of which is a traction fluid and the remainder have related structures in which the cyclohexyl rings are separated by two or three carbon atoms. Carbon‐13 spin‐lattice relaxation times have been measured at 25.16 MHz at pressures up to 200 MPa over the temperature range 280‐329 K. High‐pressure relaxation data have been successfully interpreted in terms of the ‘model‐free’ approximation. A pressure‐dependent rotational coupling parameter, κ, was evaluated from a modified Stokes‐Einstein‐Debye relationship using experimentally determined pressure‐dependent rotational correlation times. The smallest value of κ was found to be associated with the most rigid and least‐extended molecule, showing that molecular shape has a significant effect on the rotational‐translational coupling. The values obtained for the activation volumes derived from methyl group data suggest that barriers to internal motion are governed by intramolecular effects. It has been demonstrated that high‐pressure 13C relaxation measurements can provide a powerful means of studying the relationship between molecular rigidity and the macroscopic behaviour of functional fluids.
1H and 13C NMR study of 1‐substituted isatins and their corresponding 3‐(dicyanomethylidene)indol‐2‐ones
Authors: Morales‐Ríos Martha S. , Joseph‐Nathan Pedro
Published: May 2005

The assignments of the 1H and 13C NMR signals of 1‐substituted isatins and their corresponding 3‐(dicyanomethylidene)indol‐2‐ones were derived by analysis of the 13C1H spin coupling patterns and by inspection of the two‐dimensional C, H shift correlation spectra. Erroneous literature assignments have been corrected. A significant difference between the 5Δ‐deuterium isotope effects on the 13C chemical shifts of the CN groups cis and trans to the heterocyclic amide fragment (D)HNCO was observed in partially deuteriated 3‐(dicyanomethylidene)indol‐2‐one. This geometric dependence was used to assign the two CN groups that are otherwise difficult to assign.
Assignment of the 1H and 13C NMR spectra of the quinolizidine alkaloid anagyrine and determination of its conformation
Authors: Rycroft David S. , Robins David J. , Sadler Ian H.
Published: May 2005

The 1H NMR spectrum of the quinolizidine alkaloid ( − )‐ anagyrine has been studied at 200 and 600 MHz. A full assignment of the 1H signals has been achieved by application of a variety of NMR techniques, including homo‐nuclear spin decoupling, NOE difference, 2D δH/δH COSY and direct δc/δH correlation (including HMQC) experiments. The 13C NMR spectrum has also been assigned, and differences from the current literature assignments are reported. The conformation of ( − )‐anagyrine has been elucidated by consideration of the proton‐proton spin‐spin coupling constants and NOEs. The configuration of the lone pair of the tertiary amine nitrogen is β, ring B has an envelope conformation and rings C and D have chair conformations with cis‐decalin type of ring fusion between them.
13C NMR analysis of specifically labeled [13C] azobenzenes
Authors: Shine Henry J. , Subotkowski Witold
Published: May 2005

13C NMR chemical shifts and 13C13C couplings for six specifically labeled [13C] azobenzenes are reported. Coupling magnitudes depend on the position of labeling and the nature of the substituents.
Assignment of the 1H, 13C and 15N resonances in cyclodextrin nitrates by 2D NMR and the determination of the regioselectivity of the hydroxylamine‐induced denitration reactions
Authors: Bulusu S. , Axenrod T. , Liang B. , He Y. , Yuan L.
Published: May 2005

Hexakis(2,3,6‐tri‐O‐nitro)‐α‐cyclodextrin and heptakis(2,3,6‐tri‐O‐nitro)‐β‐cyclodextrin were prepared and the complete assignment of the 1H, 13C and 15N resonance signals in each case was achieved using homonuclear shift correlation experiments, one‐bond 13C1H and three‐bond 15NOC1H heteronuclear shift correlation measurements. The denitration of these cyclodextrin nitrates by hydroxylamine in pyridine was investigated to study its selectivity in preparing partially nitrated derivatives of these cyclodextrins. The sites of denitration were determined in each case using 13C and 15N NMR and the products were completely characterized. The results indicate that denitration of these cyclodextrin nitrates is a highly regiospecific reaction occurring at the 2‐position only and giving rise to hexakis(3,6‐di‐O‐nitro)‐α‐cyclodextrin and heptakis(3,6‐di‐O‐nitro)‐β‐cyclodextrin, respectively.
One‐ and two‐dimensional multinuclear magnetic resonance study of azaphospholes; sign determination of J(15N, 1H), J(31P, 1H), J(31P, 13C), J(31P, 15N); Application of hahn‐echo extended pulse sequences
Authors: Wrackmeyer Bernd , Kupče ĒRiks , Schmidpeter Alfred
Published: May 2005

Various 1,2,3‐ and 1,3,4‐diazaphospholes (1 to 4), a 1,2,3,4‐triazaphosphole (5) and two 1,2,3‐diazaphospholium chlorides (6, 7) have been studied by 13C, 15N and 31P NMR spectroscopy. The absolute signs [based on 1J(13C, 1H) > 0] of numerous coupling constants [e.g., 1J(31P, 13C) < 0, 1J(31P, 15N) > 0] have been determined by combining information from one‐dimensional selective 1H{31P}, 13C{31P} and two‐dimensional (2D) 13C/1H, 15N/1H and 31P/1H heteronuclear shift correlations. Hahn‐echo extended (HEED) pulse sequences have been applied to one‐ and two‐dimensional 31P NMR measurements. In 1D 31P NMR spectra, 1J(31P, 15N) coupling constants can be conveniently determined. The corresponding HEED 2D 31P/1H experiments yield, in addition, the long range nJ(15N1H) (n = 2,3) coupling constants (and their relative signs). Furthermore, isotope shifts, 1Δ15/14N, on 31P resonances were measured. The low frequency shifts (−0.072 to −0.114 ppm) observed here for two‐coordinate phosphorus compounds 1 to 7 are much larger than those previously reported for P(V)‐ and three‐coordinate P(III) compounds.
Solution phase 1H and 13C‐NMR studies of some 1,4,8,11,15,18,22,25‐octa‐alkylphthalocyanines
Authors: Cook Michael J. , Cracknell Steven J. , Moore Geoffrey R. , Osborne Michael J. , Williamson David J.
Published: May 2005

Solution state 1H NMR and 13C NMR spectral data are reported for 1,4,8,11,15,18,22,25‐octahexylphthalocyanine, its zinc metallated analogue, and 1,4,8,11,15,18,22,25‐octanonylphthalocyanine. Full 1H and 13C NMR signal assignments for these compounds have been made using one and two dimensional techniques supported by T1 measurements. 13C NMR spectra of the two metal‐free derivatives show only three signals in the aromatic region at 100 MHz but the expected four resonances at 22.5 MHz. The apparent absence of one of these at 100 MHz is ascribed to a fast exchange process, originating from NH ⃛N⇌N ⃛HN tautomerism.
Complete assignment of the 1H and 13C NMR spectra of norbornene derivatives
Authors: Fisher Julie , Gradwell Michael J.
Published: May 2005

The complete assignment of the 1H and 13C spectra of 2‐exo‐ and 2‐endo‐nor‐bornenemethanol is presented. Resonance assignment was achieved using 1H–1H double resonance, COSY and 1H/13C correlation spectra. Computer simulations of the H‐2 (exo or endo) proton decoupled spectrum for both isomers enabled scalar couplings to be determined.
1H NMR study of casein phosphopeptide (1–25): Assignment and conformation
Authors: Tsuda Sakae , Niki Ryoya , Kuwata Tamotsu , Tanaka Isao , Hikichi Kunio
Published: May 2005

The solution conformation of β‐casein phosphopeptide (CPP) was studied by 1H NMR spectroscopy. As a prerequisite to the conformational analysis the spectral assignment was carried out for CPP in the Ca2+‐free and ‐bound states by the use of two‐dimensional NMR spectroscopy. The assigned resonances were used for (1) pH‐titration experiments, (2) elucidation of the temperature dependence of the amide resonance and (3) a nuclear Overhauser enhancement (NOE) experiment. Although the β‐turn conformation is predicted for the sequence – Val8–Pro9–Gly10–Glu11–of CPP, the present NMR results do not provide favourable evidence for its formation.
NMR evidence for an NH+ …OC intramolecular hydrogen bond in 2‐alkyl‐3‐morpholinopropiophenones—structure of a new elevated high density lipoprotein agent in solution
Authors: Cotelle Nicole , Cotelle Philippe
Published: May 2005

7‐[2‐(4‐morpholinomethyl)butanoyl]‐4‐methyl‐2H‐1, 4‐benzoxazin‐3 (4H)‐one hydrochloride (2a) (a new elevated high density lipoproteins agent) and related compounds have been studied by NMR spectroscopy. Compound 2a exhibits an intramolecular hydrogen bond between the NH+ and CO bonds in solvents with low nucleophilicity. These results are confirmed by IR spectroscopy in solution.
Proton‐coupled carbon‐13 NMR spectra of butadienes
Authors: Harris Robin K. , Ng Soon , Connelly Alan
Published: May 2005

Proton‐coupled 13C NMR spectra were obtained for three methyl‐substituted butadienes, namely 2‐methylbuta‐1,3‐diene, trans‐2‐methylpenta‐1,3‐diene and 2,4‐dimethylpenta‐1,3‐diene. The second‐order spectra were analysed by computer, using some new 1H NMR data, and the resulting chemical shifts and coupling constants are reported. The parameters are related to conjugation (and, in turn, to conformation) of the compounds, and to the influence of σ and π pathways for coupling.
Magnitudes and relative signs of J(119Sn, 13C) and J(119Sn,H) coupling constants in some organotin(IV) compounds using 2D NMR methods
Authors: Lyčka Antonín , Jirman Josef , Holeček Jaroslav
Published: May 2005

Two‐dimensional H,C‐COSY spectra of some tetra‐, penta‐ and hexa‐coordinated organotin(IV) compounds were measured. The relative signs of nJ(119Sn,13C) and (n+1 J(119Sn,1H) coupling constants were determined after analysis of the orientation of the appropriate 119/117Sn satellites in the H,C–COSY spectra. The relative signs in BunSn and BznSn (n = 2 or 3) derivatives are opposite, whereas in Ph3Sn derivatives these signs are the same for carbon atoms in the ortho and meta positions and opposite for carbon atoms in the para positions. The same sign was found for 2J(119Sn,13C‐2) vs. 2J(119SnC1H2) in tribenzyltin(IV) chloride from the COLOC spectrum.
Multinuclear MR studies of Platinum(II) nitroimidazole complexes: 15N‐labelling and reactions with nucleotides
Authors: Macdonald Fiona M. , Sadler Peter J.
Published: May 2005

Platinum nitroimidazole complexes are potentially useful for sensitizing tumour cells towards radiation damage. We have studied reactions of cis‐[Pt(II)(MNZ)2Cl2], where MNZ is 1‐(2′‐hydroxyethyl)‐2‐methyl‐5‐nitroimidazole (metronidazole), with guanosine monophosphate (5′‐GMP) and the oligonucleotides GpC, GpG and d(GpCpGpC) using 1H NMR spectroscopy. The complex [Pt(MNZ)2(5′‐GMP)2]Cl2 · 7H2O was isolated and characterized. Novel syntheses of cis‐ and trans‐[Pt(15N‐DMZ)2Cl2], where DMZ is 1,2‐dimethyl‐5‐nitroimidazole (dimetridazole), and NMR spectra of 15N‐enriched intermediates in the ligand synthesis, and of these complexes are discussed. Reactions of the enriched cis complex with 5′‐GMP were investigated by NMR spectroscopy.
Multinuclear high‐resolution solid‐state magnetic resonance studies of some platinum(II) complexes with phosphorus‐containing ligands
Authors: Harris Robin K. , McNaught Ian J. , Reams Patrick , Packer Kenneth J.
Published: May 2005

Cross‐polarization, magic‐angle spinning NMR experiments have been carried out for nine square‐planar platinum(II) complexes, each with two substituted phosphine ligands. 13C and 13P (and, in some cases, 195Pt) nuclei were observed. The results reveal crystallographic non‐equivalence which, in one instance, is confirmed by subsequent X‐ray studies. Chemical shifts and coupling constants—(Pt,P), (Pt,C), (P,C) and, for one compound, (Sn,P)—are reported and discussed. Shielding tensor data are also presented.
Solution structure of [(triphos*)RhH2(AuPPh3)3][PF6]2 deduced by one‐ and two‐dimensional 1H{31P} and 1H{103Rh} double‐resonance techniques
Authors: Imhof Daniel , Rüegger Heinz , Venanzi Luigi M. , Ward Thomas R.
Published: May 2005

The application of 1H{31P} and 1H{103Rh} double‐resonance techniques for the elucidation of the solution structure of the metalla‐tetrahedrane clusters of the [(triphos*)RhH2(AuPPh3)3][PF6]2 type, with the chiral tripodal phosphine triphos* [RRR/SSS‐ or RRS/SSR‐1,1,1,‐tris(methylphenylphosphinomethyl)ethane] is described. Variable‐temperature studies revealed three types of dynamic processes, i.e. rapid rotation of the trigold moiety (AuPPh3)3, mutual exchange of the diastereotopic hydrides and slow rotation of the RRS/SSR‐triphos* unit in one diastereomer.
Comparison of solid‐state and solution structures of (R3P)2CdX2, (Et3P)2Cd2X4 and (Bu3P)3Cd2X4 complexes
Authors: Kessler Janet M. , Reeder Jonathan H. , Vac Rahel , Yeung Constance , Nelson John H. , Frye James S. , Alcock Nathaniel W.
Published: May 2005

The cadmíum (II) phosphine complexes (Et3P)2Cd2X4, (R3P)2CdX2 [R3P = Ph3,P, Bu3P, Et3P, 1‐phenyldibenzophosphole (DBP), and 1‐phenyl‐3,4,‐dimethylphosphole (DMPP)] and (Bu3P)3Cd2X4 (X = Cl, Br, I) have been prepared and their solution and solid state structures determined by a combination of elemental analyses, conductance, infrared and NMR spectroscopy. The structures of (Ph3P)2CdI2 (1) and (DBP)2CdI2 (2) have been determined from three‐dimensional X‐ray data collected by counter methods. Compound 1 crystallized in space group P21,/a with a = 18.312 (9), b = 10.285 (5), c = 19.311 (9) Å, β = 115.53 (4)° and Z = 4. Compound 2 crystallized in space group P21,/n with a = 12.698 (3), b = 15.302 (4), c = 17.477 (4) Å, β = 96.66 (2)° and Z = 4. The structures were refined by least‐squares methods with RF = 0.041 and 0.048 for 4157 and 3393 unique reflections with I/σ(I) ⩾ 2.0 for 1 and 2, respectively. Both molecules deviate from ideal C2v symmetry and have very slightly different Cd‐I (1; 2.724 (2), 2.731 (2); 2; 2.718 (1), 2.721 (1) Å) and Cd‐P (1, 2.631 (2), 2.653 (2); 2; 2.616 (3), 2.603 (3) Å) bond distances. The Cd‐P bond distance differences are sufficient to give rise to a second order ABX CP/MAS 31P{1H} NMR spectrum for 1 but for 2 the phosphorus nuclei of the two DBP ligands are chemical shift equivalent. The CP/MAS 113Cd{1H} NMR spectra of both compounds 1 and 2 show apparent first order triplets. The (Bu3P)3Cd2X4 complexes are shown by variable temperature 31P{1H} NMR and conductance measurements to exist in solution as equilibrium mixtures of (Bu3P)2Cd2X4 and (Bu3P)2CdX2. CP/MAS 31P{1H} and 113Cd{1H} NMR spectra suggest that these compounds exist as doubly halide bridged (R3P)2Cd(μ‐X)2CdX2(R3P) species containing four‐ and five‐coordinate cadmium in the solid state. Equilibrium and activation thermodynamics for the ligand exchange processes of representative complexes have been determined from variable temperature 31P{1H} NMR spectra in CDCl3/CH2Cl2 (1:1) solutions.
Interactions and 2D NOESY. Pd(II) and Pt(II) cylometallation chemistry
Authors: Pregosin Paul S. , Wombacher Franz
Published: May 2005

Phase sensitive,1H 2D NOESY measurements have been made on a variety ofN,N′‐dimethylbenzylamine cyclopalladated complexes with coordinated ligands having pendant CH moieties. For 8‐methylquinoline and benzo [h] quinoline it can be shown that the quinoline‐methyl and benzoquinoline CH‐10 moieties, respectively, reside in a pseudo fifth coordination position above the square planar complex. This information arises primarily from NOEs from one NCH3and H3′, the protonorthoto the PdC bond. Similar NOESY studies have also been carried out for (i) a cyclopalladated aliphatic analog based on Pd(NO3(L){N(CH3)2CH2C (CH3)(OCH3)CH2} and (ii) a cyclopalladated phosphite (C∩oP), of the form Pd(NO3)(L){P(OEt)2OC6H4}. New platinum complexes of the typetrans‐[PtCl2L (tertiary phosphine or tertiary arsine)] are presented, and the spin–spin coupling constants from the pendant CH of L to the195Pt are discussed. Several of these complexes can exist in two geometric forms, i.e., for the phosphite complexes: Ptransto N, Ctransto O as against Ptransto O, Ctransto N. A distinction between these isomers is made using the same1H NOESY spectra that provide information concerned with the pendant CH functions.
13C NMR study of N‐acyl‐ and N‐sulphonyl‐isatins and their ring‐opened derivatives
Authors: Angell E. Charles , Black David St C. , Kumar Naresh
Published: May 2005

The complete assignments of the 13C NMR resonances of 1‐acetyl‐, 1‐benzoyl‐, 1‐benzenesulphonyl‐, 1‐methanesulphonyl‐ and 1‐(2‐nitrobenzenesulphonyl)‐isatins and their ring‐opened glyoxylic derivatives are reported. The 13C assignments of acylisatins were derived from isatin as a model, while assignments of glyoxylic derivatives were made by complete assignment of compound 8b together with its use as a model.
1H and 13C two‐dimensional NMR study of magainin 1
Authors: Yu Chin , Yang Ta‐Horng
Published: May 2005

The 1H and 13C NMR spectra of magainin 1, a sterilizing agent of the skin, were studied using two‐dimensional techniques. All the 1H and 13C NMR resonances were unambiguously determined from a combination of 2D homo‐ and heteronuclear NMR spectroscopy.
Measurements of heteronuclear dipolar powder patterns due only to directly bonded couplings
Authors: Nakai Toshihito , Terao Takehiko
Published: May 2005

A method is proposed which allows a simple Pake doublet due only to the directly bonded CH pair to be obtained by measuring the local field at the position adjacent to a 13C nucleus under proton homonuclear decoupling. This approach allows precise determination of the CH distance even in compounds with high proton density.
13C and 19F nuclear magnetic resonance spectra of multisubstituted methanes
Authors: Takeuchi Yoshio , Itoh Noriaki , Koizumi Toru , Yamagami Chisako , Takeuchi Yoshito
Published: May 2005

The 13C and 19F (when appropriate) chemical shifts of a variety of di‐, tri‐ and tetrasubstituted methanes of the type CH2XCOOEt (I), CHXYCOOEt (II) and CXYZCOOEt (III), where the substituents X, Y and Z are F, Br, OEt, OPh, SEt, SPh and NO2, were determined. The prediction of the observed C‐α chemical shifts of I, II and III based on the simple additivity of substituent effects in monosubstituted methanes [MeX; SCS(IV)] is not satisfactory, although those of I are well correlated with SCS (IV). The C‐α chemical shifts of II and III can be correlated in terms of the multi‐parameter analysis of individual SCS (I), the difference between δ (CH2XCOOEt) and δ (CH3COOEt). The origin of the chemical shifts is discussed. The 19F chemical shifts of I, II and III were also satisfactorily analysed in terms of σI and σ.
Natural abundance 17O NMR spectra of thio analogues of chromanones, chromones, flavanones and flavones
Authors: Duddeck Helmut , Lévai Albert
Published: May 2005

The 17O NMR data of thio analogues of chromanones, chromones, flavanones and flavanones are compared with those of corresponding oxygen analogues. Substituent effects are discussed in terms of steric and electronic interactions and also the conformational behaviour of some substituents and the hetero ring.
Easy implementation of selective INADEQUATE and HCC relay experiments using heteronuclear chemical shift filtering
Authors: Kövér Katalin E. , Uhrin Dušan , Liptaj Tibor , Batta Gyula
Published: May 2005

The application of a chemical shift selective filter in 1D INADEQUATE and HCC relay experiments is proposed. It is demonstrated that highly selective filtering can be the equivalent of low‐power excitations. Applications to the selective detection of carbon–carbon connectivities are presented.
EPR study of pyrrolyl‐1‐oxyl and 3‐pyrrolinyl‐1‐oxyl radicals
Authors: Crayston Joe A. , Kakouris Costas , Walton John C.
Published: May 2005

Pyrrolyl‐1‐oxyl, 3‐phenylpyrrolyl‐1‐oxyl and a number of deuterium‐substituted derivatives were generated by hydrogen abstraction from the corresponding N‐hydroxypyrroles, and observed by EPR spectroscopy. They were all transient with lifetimes ≤ 10−2 s. The hyperfine splittings showed that unpaired spin was delocalized around the five‐membered ring with significant density at N‐1, C‐3 and C‐4, but very low density at C‐2 and C‐5. N‐Hydroxpyrrole and pyrrolyl‐1‐oxyl were studied by the semi‐empirical AM1 method, and the radical by the INDO method. The transient pyrrolinyl‐1‐oxyl was also generated from the corresponding N‐hydroxypyrroline and observed by EPR spectroscopy.
ESR and ENDOR study of 2,3‐dihydro‐1‐oxo‐1λ4,2,3,5‐thiatriazol‐3‐yl radicals
Authors: Neugebauer Franz A.
Published: May 2005

Dehydrogenation of 2,5‐dihydro‐1,2,3,5‐thiatriazole 1‐oxides with thermally formed bis(4‐methylphenyl)aminyl generated 2,3‐dihydro‐1‐oxo‐1λ4,2,3,5‐thiatriazol‐3‐yl radicals. ESR, ENDOR and triple resonance studies in combination with 15N labelling yielded the magnitude and assignment of all 1H and 14N hyperfine coupling (HFC) constants. The radicals have a basic five‐π‐electron amidrazon‐2‐yl structure with the highest spin density at N‐2.
Apramycin: Complete 1H and 13C NMR assignments and study of the solution conformation by ROESY measurements
Authors: Szilágyi László , Puzstahelyi Zita Sz.
Published: May 2005

Complete and self‐consistent assignments have been achieved, through the concerted use of various 2D techniques, for the 1H and 13C NMR spectra of the free base and protonated forms, respectively, of apramycin (1) in D2O solution. It is shown that J‐relayed dipolar (or J/R) and coherent transfer (HOHAHA) processes in ROESY experiments can hardly be eliminated with spin systems such as that studied here. True ROE cross‐peaks can, nevertheless, be identified by varying the experimental conditions. The solution conformation of 1 has been characterized based on the ROESY data, proton‐proton coupling constants and 13C T1 measurements. The 4‐aminoglucose unit appears to be locked together with the octodiose fragment in a conformation satisfying the requirements of the exo‐anomeric effects around the C‐1"OC‐8′ bond; the 2‐deoxystreptamine unit, on the other hand, enjoys more rotational freedom around the respective glycosidic bond. The undistorted chair conformations of all six‐membered rings in 1, and the overall conformation of the molecule, are totally independent of the pH, i.e. the protonation state of the molecule.
Compounds with bridgehead nitrogen 68—NMR spectra and stereochemistry of perhydropyrido [1,2‐c] [1,3]oxazines
Authors: Crabb Trevor A. , Ingate Simon T. , Nevell Thomas G.
Published: May 2005

Low‐temperature 13C NMR spectroscopy shows perhydropyrido [1,2‐c] [1,3]oxazine to adopt a conformational equilibrium in CD2Cl2–CFCl3 solution containing 98% trans fused conformer in equilibrium with 2% O‐outside‐cis fused conformer at 203 K. A similar equilibrium position is adopted by the trans‐(H‐4,H‐4a)‐4‐methylperhydropyrido[1,2‐c][1,3]oxazine, whereas the C‐4 epimer adopts exclusively the trans fused conformation.
ESR studies of deuteriated polycyclic aromatic radical cations
Authors: Sang Hong , Wang Hanqing
Published: May 2005

Several deuteriated polycyclic aromatic radical cations were studied by ESR. Their hyperfine coupling constants are reported and mechanisms for their formation are proposed.
119Sn NMR characterization of the series of complex [Pt(SnClxBry)5]3− Anions (x + y = 3) extracted into chloroform using a liquid anion exchanger
Authors: Koch Klaus R.
Published: May 2005

In the presence of excess SnCl2 or SnBr2, 119Sn NMR spectroscopy shows that the complex anions [Pt(SnCl3)5]3− or [Pt(SnBr3)5]3− are exclusively extracted into chloroform containing methyltrioctylammonium chloride or bromide. Significantly, in the presence of even small amounts of chloride ion, halogen scrambling of the [Pt(SnBr3)5]3− complex anion occurs, resulting in a distribution of the [Pt(SnClxBry)5]3− species, all possible isomers of which can be observed in this solvent system at room temperature.
Solvent‐induced variations in nitrogen NMR shieldings of tert‐butyl isocyanide as a probe for solvent polarizability–polarity
Authors: Witanowski Michal , Sicinska Wanda , Webb Graham A.
Published: May 2005

The nitrogen NMR shielding of tert‐butyl isocyanide (1) is shown to be a sensitive probe of solvent polarizability–polarity, since the shielding is demonstrated to be unresponsive to hydrogen bonding effects between 1 and the solvent. The direction of solvent effects observed is explained in terms of the solvaton model, used within the INDO/S–SOS framework. A comparison is made with solvent‐induced nitrogen shielding variations of the corresponding isomeric covalent cyanides.
Nuclear spin relaxation in proteins and models at low temperature
Authors: Marshall Eric A. , Bryant Robert G.
Published: May 2005

13C NMR spectra were obtained using cross‐polarization methods at temperatures near 5 K to examine the magnetization transfer spin dynamics and the practicality of routinely making low‐temperature measurements as a means for gaining sensitivity. The magnetization transfer rate between protons and carbon was generally found to be more rapid at 5 K than at room temperature, and the proton and carbon relaxation times in the rotating frame were considerably longer. Both conspire to improve the sensitivity of the cross‐polarization experiment. The limiting factor in the ease of executing the experiment rapidly is the value for the proton spin–lattice relaxation time, which in samples with few methyl groups may become much longer than is common at higher temperatures. However, when the methyl group concentration is high, the proton spin–lattice relaxation rate at 5 K may be in the range of seconds, making the low‐temperature experiment a highly sensitive and practical opportunity.
Carbon‐13 nuclear magnetic resonance. Study of 2‐halopicolines, their N‐oxides and 2‐halo‐4‐nitropicoline N‐oxides
Authors: Puszko Aniela
Published: May 2005

The 13C NMR spectra of 2‐halopicolines, 2‐halopicoline N‐oxides and 2‐halo‐4‐nitropicoline N‐oxides were recorded and their chemical shifts assigned. The influence of the electronic properties of the substituents on the direction of the chemical shifts is discussed.
Investigation of phase‐sensitive 13C‐detected 13C1H shift correlation sequences with partial and full 1H1H decoupling and partial spectral editing
Authors: Carpenter Katharine A. , Reynolds William F.
Published: May 2005

Several different versions of the 13C‐detected 13C1H shift correlation sequence in phase sensitive mode with partial and full 1H1H decoupling are described and evaluated. As expected, they show sensitivity advantages over their absolute value analogues. Further, it is possible partially to edit the 2D spectra since CH2 peaks are inverted relative to CH and CH3 peaks.
NMR and theoretical investigation of dicylopentadiene derivatives
Authors: Bakke Jan M. , Brænden Jon Erik , Krane Jostein
Published: May 2005

The 1H and 13C NMR spectra of endo‐tricyclo[5.2.1.02,6]deoane (1‐H), endo‐tricyclo[5.2.1.02,6]decan‐2‐ol (1‐OH) and 2‐endo‐tricyclo[5.2.1.02,6]decanyl acetate (1‐OAc) were assigned by the use of 1H1H, 1H13C and 13C13C correlation spectra. The substituent chemical shifts were similar to those observed for the analogous norbornane derivatives.2 The flip angle of the five‐membered ring and the conformational composition were estimated from the vicinal 1H1H coupling constants. The results were compared with those from molecular mechanics calculations (MMPMI) and semi‐empirical molecular orbital calculations (MNDO). The geometries obtained from the NMR data were close to those from the MMPMI calculations, and the calculated and observed energy differences were within ± 2 kJ mol−1 of each other. The endo conformation of the five‐membered ring was found to be most stable for both 1‐OH and 1‐OAc. The MNDO calculation indicated a close to planar five‐membered ring to be the most stable. This result could not be accommodated with the NMR data.
13C, 15N, 29Si and 31P NMR study of N‐trimethylsilylaminophosphorus compounds: Sign determination of coupling constants and application of Hahn‐echo extended pulse sequences
Authors: Wrackmeyer Bernd , Kupče Ēriks , Kehr Gerald , Schiller Jürgen
Published: May 2005

N‐Trimethylsilylaminophosphorus compounds containing phosphorus in different oxidation states [P(III) and P(V)] and with different coordination numbers (2, 3 or 4) were studied by 13C, 14N, 29Si and 31P NMR, using a variety of one‐ and two‐dimensional (2D) techniques, including Hahn‐echo extended (HEED) pulse sequences. These techniques were demonstrated by the determination of the signs of all coupling constants involving the 1H, 13C, 15N, 29Si and 31P nuclei in bis(trimethylsilyl)aminodimethylphosphane (1). Appropriate experiments, including inverse 2D 1H{15N} correlations, were performed for the other compounds in order to determine the signs of the coupling constants. A geometric dependence of 2J(31P, N, 29Si) was proved for bis(trimethylsilyl)amino(tert‐butyl)chlorophosphane (2c), where large negative 2J(31P,29Si) and a small positive 2J(31P,29Si) values, indicate syn and anti orientations, respectively, of the NSi bond relative to the phosphorus lone pair of electrons. The HEED pulse sequences allow the rapid determination of isotope‐induced shifts, 1δ15/14N(31P), as shown for 1, derivatives of 1 and 2c.
NMR study of some anthraquinones from rhubarb
Authors: Danielsen Knut , Aksnes Dagfinn W. , Francis George W.
Published: May 2005

The 1H and 13C NMR spectra of the anthraquinones physcion, emodin, chrysophanol, aloe‐emodin and rhein were assigned. The previously preferred assignments for C‐2 and C‐4 in physcion were reversed. The NOE technique was used for the assignment of the 1H signals and SEFT and/or heteronuclear decoupling for 13C resonances.
Substituent effects on the 13C NMR spectra of ethyl cis‐ and trans‐2‐(p‐substituted‐phenyl)‐1‐cyclopanecarboxylates
Authors: Kusuyama Yoshiaki , Tokami Kenjiro
Published: May 2005

13C NMR spectra were measured for a series of ethyl cis‐ and trans‐2‐(p‐substituted ‐ phenyl) ‐ 1 ‐ cyclopropanecarboxylates. The effects of the para substituents and the geometry on the chemical shifts are discussed.
Total assignment of the 1H and 13C spectra of peridinin
Authors: McLean Stewart , Reynolds William F. , John Lisa M. D. , Tinto Winston F.
Published: May 2005

Complete 1H and 13C spectral assignments are reported for peridinin, the major dinoflagellate carotenoid responsible for ‘red tides’ in the ocean. These assignments were made with the aid of HETCOR, FLOCK and COSY 2D spectra and NOE difference spectra.
Improved strategy for sequence‐specific 13C NMR assignments in [d(CGTACGTACG)]2
Authors: Wang Ke Yu , Heffron Gregory J. , Bishop Karl D. , Levy George C. , Garbesi Anna M. , Tondelli Luisa , Medley James H. , Borer Philip N.
Published: May 2005

13C resonances of [d(CGTACGTACG)]2 were assigned by heteronuclear multiple quantum coherence and longrange heteronuclear multiple coherence. The maximum likelihood method was used for the sugar regions of the HMQC spectrum, which made it possible to assign unambiguously all the C‐2′ carbons and some of the C‐5′ carbons.
Reorientational dynamics and internal mobility of [Lys8]‐vasopressins by analysis of 13C, 15N and 1H NMR relaxation
Authors: Zieger G. , Sterk H.
Published: May 2005

The dynamic behaviour of [Lys8]‐vasopressin derivatives, especially of N‐Gly‐Gly‐Gly‐[Lys8]‐vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from 13C spin–lattice relaxation times, T1, spin–spin relaxation times, T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co‐workers and the ‘model‐free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108–109 s−1, we observe a faster mobility of the order of 109–1010 s−1 in addition to slow dynamic contributions. The latter can be associated by means of T1, measurements with a motion involving the SS linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from 13C relaxation were corroborated by 15N T1 measurements, performed at the 15N natural abundance level by an INEPT–reverse INEPT method, and by 15N NOE investigations.
Solvent effects on the 1H1H, 1H19F and 19F19F coupling constants of fluorobenzene and 1,2‐difluorobenzene
Authors: Suntioinen Sirpa , Laatikainen Reino
Published: May 2005

The 1H and 19F NMR spectra of fluorobenzene and 1,2‐difluorobenzene were measured in several pure solvents and in binary solvent mixtures to study the solvent dependence of 1H19F and 19F19F coupling constants. The solvents are distinctly divided into two groups on the basis of their hydrogen bonding properties. Most the coupling constants increase with increasing polarity of the solvent within both groups. The 3J(F,H) and 4J(F,H) coupling constants are typically increased by 4‐7% when the solvent is changed from cyclohexane to acetone. For the 5J(F,H) coupling of fluorobenzene the change is as large as 70%.
Carbon‐13 NMR chemical shift substituent effects 8—3‐monosubstituted 2‐methylpropenes
Authors: Rittner Roberto , Braibante Mara E. F.
Published: May 2005

13C NMR chemical shifts for some 3‐heterosubstituted 2‐methylpropenes are reported. The α‐methylene chemical shifts show excellent linear correlations with the corresponding data for some substituted carbonyl compounds (propanones, methyl acetates and N,N‐diethylacetamides). Their estimated intramolecular interaction shifts are indicative of electronic interactions between the heteroatom and the ethylenic double bond. The sp2 carbon shifts calculated by Dorman et al.'s method, taking a proposed set of βσ and βπ parameters, are in close agreement with the experimental values. Neither the α‐methylene nor the olefinic carbon chemical shifts correlate well with the usual electronic and steric parameters of the substituents.
Stereochemistry of crown ethers. V.—solution structure and complexational behaviour of dibenzo crown ethers
Authors: Stoss S. , Schroth W. , Kleinpeter E.
Published: May 2005

The preferred conformations and the complexing behaviour of 16‐ and 17‐membered dibenzo crown ethers were studied by means of both NMR spectroscopy and molecular mechanical calculations. Conclusions could be drawn about the stoichiometry and stability of the alkali metal ion corand complexes. The spin–lattice relaxation times of the crown ether carbon atoms and the relevant complexes are discussed with respect to the intramolecular flexibility of these species. The intramolecular reorientations detected are reduced considerably in the alkali metal ion complexes. In the preferred conformers of corands 2, 3 and 6, the molecular mechanical calculations prove that the phenyl rings are positioned in a chair conformation at a twist to each other. The same phenyl rings in the crown ethers 1, 4 and 5 are in a boat conformation. These conformations seem to be important for the optimum complexation of the alkali cations.
195Pt NMR study of (η5‐cyclopentadienyl)trialkylplatinum(IV) complexes
Authors: Boardman Larry D. , Newmark Richard A.
Published: May 2005

195Pt NMR data are reported for a series of (η5‐cyclopentadienyl)trialkylplatinum(IV) complexes. Chemical shift differences are rationalized primarily on the basis of substituent electronic properties. Changes in solvent produce relatively modest changes in chemical shift, and the dependence of the chemical shift on temperature and concentration is sufficiently strong to warrant control of these variables for comparative measurements. An improved synthesis of [IPtMe3]4 is also described.
1H NMR and 19F NMR chemical shifts of fluorinated retinals, Schiff bases and protonated Schiff bases
Authors: Colmenares Leticia U. , Liu Robert S. H.
Published: May 2005

Fluorine‐induced shifts of neighbouring protons were studied by comparing the 1H NMR data of 20 fluorinated retinal isomers and their non‐fluorinated counterparts. Concurrent 19F NMR data of various isomers, analysed with respect to those of the all‐trans fluorinated isomers, showed an interactive effect between the γ‐protons and F. Successful application of the observed trends in 1H NMR and 19F NMR chemical shifts to retinylidene Schiff bases and protonated Schiff bases demonstrates their importance as practical aids in assigning configuration and predicting relative 1H NMR and 19F NMR resonances.
Spectroscopic analysis of 3β‐acetoxy‐8‐hydroxy‐8,11‐epoxy‐8,9‐seco‐6,11‐cyclolanostane‐7,9‐dione
Authors: Fujiwara Fred Y. , Rehder Vera G. , Marsaioli Anita J.
Published: May 2005

Spectroscopic analysis of a lanostane derivative, which was synthesized with a view to its application as an intermediate in chiral building block syntheses, is presented together with the conformational analysis of a secolanostane‐7‐8‐9,11‐tetraone.
1H and 13C NMR studies of the proton transfer in complexes of substituted phenols with trimethylamine N‐oxide
Authors: Brycki Bogumil , Brzezinski Bogumil , Zundel Georg , Keil Thomas
Published: May 2005

Substituted phenol–trimethylamine N‐oxide (TMAO) systems were studied. The 1H chemical shift of the hydrogen‐bonded proton first increases with decreasing pKa of the phenols and, after a sharp maximum, it then decreases. Thus, the shielding of the hydrogen‐bonded proton by the O atom of the phenol first decreases, and this proton is most deshielded in the 3,4‐dinitronphenol–TMAO system. With a further decrease in the pKa of the phenol this proton becomes shielded again by the O atom of the TMAO molecule. This behaviour of the 1H NMR signal is in very good agreement with the changes in the shape of the proton potential obtained from IR spectra. In the case of the strongest hydrogen bond, in the 3,4‐dinitrophenol‐TMAO system, the 13C signals are considerably broadened, probably owing to the long lifetime of this bond. Δ14 Values were calculated from the 13C NMR signals, which should also reflect the changes in the nature of the phenol—TMAO hydrogen bonds. A small difference is obtained between the results obtained from the 13C and 1H NMR spectra. This difference is caused by the effects of the substituents on the 13C NMR signals, which are not taken into account in the calculation of the Δ14 values.
15N NMR, 1H NOE difference spectroscopy and conformation of N‐(o‐aminophenyl)‐N′‐alkylureas
Authors: Jean‐Claude Bertrand J. , Just George
Published: May 2005

The 15N NMR spectra of five N‐(o‐aminophenyl)‐N′ substituted ureas and their hydrochloride salts were recorded in DMSO. N‐1 was more shielded in these ureas than in N‐phenyl‐N′‐methylurea. The shifts of N‐3 varied with the substituents. Proton exchanges at N‐3 were observed when the spectra of the hydrochloride salts were recorded. The preferential trans‐trans orientation of the protons with respect to the carbonyl in the ureido group was confirmed by NOE difference spectroscopy. In the solid, the conformation of N(o‐aminophenyl)‐N′‐methylurea, which was determined by x‐ray diffraction, was found to be similar to the suggested conformation in solution; the 15N shifts of this compound in the solid state were determined by 15N cross‐polarization magic angle spinning NMR.
High‐field 1H and 13C NMR spectra of synthetic protostane derivatives: Total assignment by 2D NMR
Authors: Paryzek Zdzislaw , Martynow Jacek , Shimo Tetsuro
Published: May 2005

Triterpenes with the protostane skeleton, which are available from biomimetic rearrangements of lanostane derivatives, were analysed by one‐ and two‐dimensional high‐field 1H and 13C NMR spectroscopy. Complete assignments of the proton and carbon signals of 11α‐acetoxy‐3β‐benzoyloxy‐5α.9β‐protost‐13(17)‐ene (4) and of 11α‐acetoxy‐31‐nor‐5α,9β‐protost‐13(17)‐en‐3‐one (5) are presented. The assignments were largely determined using substituent chemical shift and conformational effects and by a combination of DEPT, 1H‐‐1H COSY, 1H‐‐13C HETCOR and XCORFE spectra. Nuclear Overhauser effect and lanthanide‐induced shift experiments were also useful for assignments. The results confirm the structure of 4 proposed previously on the basis of the low‐resolution spectra, and provide evidence for the structure of the new fusidane 5. The effect of methyl substitution at the 4β‐position on the 13C chemical shifts is briefly discussed. The assignment of the sp2 carbon atom signals reported for diacholest‐13(17)‐enes is revised on the basis of the XCORFE experiments.
Spin‐trapping artifacts on addition of polyacrylonitrile and poly(methyl methacrylate) to dimethyl sulphoxide
Authors: Cheetham Paul F. , Cutting Graham R. , Tabner Brian J.
Published: May 2005

An ESR spectrum is observed when a sample of polyacrylonitrile powder is dissolved in a dimethyl sulphoxide solution of nitrosobenzene at room temperature. However, the spectrum is not associated with the trapping of occluded radicals from within the polymer latex, but with the hydrogen atom adduct. [Similarly, when an aqueous emulsion of poly(methyl methacrylate) is added in place of the polyacrylonitrile powder the spectrum of the hydrogen atom adduct is again observed.] Experiments in dimethyl‐d6 sulphoxide indicate that the hydrogen atom does not originate from the solvent. At higher temperatures (383 K) the spectrum of a mixture of the hydrogen atom and methyl radical adducts is observed. Experiments in dimethyl‐d6 sulphoxide show that the latter radical originates from the solvent.
13C NMR spectra of tricyclic diaziridines and their data‐base forecasts
Authors: Kaupp G. , Denisenko S. N.
Published: May 2005

The 13C NMR data for tricyclic and bicyclic diaziridines with condensed five‐ and six‐membered rings are interpreted and compared with the forecast of the C13‐NMR/IR data‐base (successor: SPECINFO data‐base). There are large differences in chemical shifts and large deviations in the forecasts. Bond angles from semi‐empirical AM1 calculations with geometry optimization correlate with the observed shifts. Similar behaviour is found for some known bicyclic diaziridines, and this is also discussed together with some known 13C shift variations in other diaziridines and bicyclic hydrocarbons. It is suggested that the widely used data‐base should include subset search facilities in order to minimize the risk of misassignments. This would allow specific effects, such as those of bond angles in cyclic compounds, to be taken into consideration.
Tautomerism in some alkyl carboxylates of amino‐substituted dihydrobenzoxazepine thiones and dihydrobenzodiazepine thiones studied by 2D NMR spectroscopy. Some stereochemical effects on 2J(C, H) and 3J(C, H) couplings
Authors: Pihlaja Kalevi , Simeonov Mario , Michalik Manfred , Peseke Klaus , Sinnwell Volker , Voss Jurgen
Published: May 2005

The 1H and 13C NMR spectra of some alkyl carboxylates of amino‐substituted dihydrobenzoxazepine thiones and dihydrobenzodiazepine thiones were recorded in CDCI3, and DMSO solutions, and the complete spectral assignments performed with 1D and 2D techniques. A solvent‐dependent tautomerization was established for the oxazepine derivatives, whereas the diazepines existed in the same tautomeric form in both solvents. The tautomeric structures are stabilized by strong intramolecular hydrogen bonding. Differences in the CH couplings are related to the stereochemistry of the tautomeric structures.
13C NMR spectra of eudesmane derivatives
Authors: Marco J. Alberto , Sanz Juan F. , Carda Miguel
Published: May 2005

The 13C NMR spectral data of 18 eudesmane derivatives, mainly acids and esters of natural and synthetic origin, are reported, and the γ‐effect of the epoxide ring in two diastereoisomeric epoxy esters is discussed.
ESR spectroscopy of some dicyano‐, pyrazino‐ and quinoxalino‐1,3,2‐dithiazolyl radicals
Authors: Chung Yuen‐Li , Fairhurst Shirley A. , Gillies Duncan G. , Kraft Gregor , Krebber Angelika M. L. , Preston Keith F. , Sutcliffe Leslie H. , Wolmershäuser Gotthelf
Published: May 2005

Several symmetrical 1,3,2‐dithiazol‐2‐yl radicals have been examined that have in common nitrogen‐containing substituents at the 4‐ and 5‐positions, namely 4,5‐dicyano‐1,3,2‐dithiazol‐2‐yl, [15N2]‐1,3,2‐dithiazolo [4,5‐b] pyrazin‐2‐yl and 1,3,2‐dithiazoleo [4,5‐b] quinoxalin‐2‐yl. The ESR spectrum of the 4,5‐dicyano radical does not reveal any 14N splittings from the cyanide groups; however, the pyrazine and the quinoxaline derivatives do have multi‐lined well resolved spectra arising from substantial hyperfine interactions with these nuclei. The interactions are sufficiently large to be observed in the powder spectra of the latter. The presence of proton hyperfine interactions shows that unpaired‐electron spin density is delocalized over all the rings. It has been found that the radicals attached to pyrazine and quinoxaline can be incorporated into single crystals of naphthalene and phenazine, respectively.
Effect of N‐methylation on the conformation of 2‐phenylbenzimidazole, 2‐phenylindole and three related rotationally constrained indoles
Authors: Amat‐Guerri Francisco , Catalán Javier , Mena Elena , Fabero Fernando
Published: May 2005

N‐Methylation of 2‐phenylbenzimidazole, 2‐phenylindole and three 3,2′‐methylene‐bridged 2‐phenylindoles gives rise to significant changes in the chemical shifts of the protons close to the phenyl‐‐‐heterocycle bond. The observed upfield and downfield shifts are accounted for by deviation from a planar conformation in the non‐rigid molecules and by intramolecular compression effects in the more rigid molecules, respectively.
Determination of long‐range 1H13C coupling constants of cis‐verbenol by modified 2D J spectroscopy
Authors: Parella Teodor , Sánchez‐Ferrando Francisco , Virgili Albert
Published: May 2005

Known selective 2D J‐resolved methods for the determination of long‐range proton–carbon coupling constants, nJ(C, H), have been modified and improved by introducing an INEPT or refocused INEPT sequence as a preparation period in the Bax–Freeman selective spin–flip method, or using exclusively selective pulses from the decoupler channel in the selective INEPT‐2D experiment. The greater sensitivity achieved allowed the determination of these couplings, even for quaternary carbons, in a short acquisition time and with excellent reproducibility for cis‐verbenol.
Complete 1H and 13C NMR assignments for apramycin, sisomicin and some N‐ and N,O‐polyacetylated aminoglycosides
Authors: Eneva Galya I. , Spassov Stefan L. , Haimova Marietta A. , Sandström Jan
Published: May 2005

The 1H NMR spectra (300 MHz) of the aminoglycoside antibiotics apramycin and sisomicin (free bases) were completely analysed by 1D and 2D methods (mainly 1H1H and 1H13C shift‐correlation spectroscopy). The complete 1H nd 13C NMR assignment of a series of semisynthetic N‐polyacetyl‐ and N,O‐polyacetyl derivatives of kanamycins A and B, tobramycin, apramycin and sisomicin was also achieved via these techniques. The effect of acetylation on the 1H and 13C chemical shifts, 1H1H coupling constants and ring conformations is discussed. The vicinal coupling constants for the unsaturated ring in sisomicin, calculated on the basis of the energetically favoured conformation predicated by the MMP2 method, are in good agreement with the experimental data.