bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of two‐dimensional shift correlated NMR techniques to the structure determination of an unusual marine alkaloid, isosaraine‐2
Authors: Cimino G. , Fontana A. , Madaio A. , Scognamiglio G. , Trivellone E.
Published: May 2005

An extensive application of two‐dimensional proton–proton and proton–carbon shift correlated spectroscopy allowed the structural elucidation of isosaraine‐2, a minor component of an unique family of alkaloids from the sponge Reniera sarai.
Increased resolution in proton detected heteronuclear NMR experiments by folding in the hetero‐dimension
Authors: Schmieder P. , Zimmer S. , Kessler H.
Published: May 2005

Limited resolution in indirect detected frequency dimensions (evolution periods) in multi‐dimensional spectroscopy is a common problem, especially in the carbon dimension of heteronuclear experiments. Folding of signals in empty regions can overcome these problems. To record the spectra in a pure phase certain conditions have to be fulfilled to account for unavoidable deviations from zero time of the zero increment. A new slight variation of inverse heteronuclear correlation pulse sequences is proposed to allow pure phase spectra. Practical applications are given.
13C NMR study of N‐substituted 3‐azachalcones
Authors: Szajda Maria
Published: May 2005

13C NMR data are reported for new N‐benzyl and N‐alkyl derivatives of 3‐azachalcone. The unambiguous assignment of signals is based on 13C/1H heteroshift correlated 2D NMR spectra.
Multinuclear magnetic resonance study of organometallic substituted enamines—stereochemical dependence of vicinal 119Sn–15N spin–spin couplings
Authors: Kupče Ēriks , Wrackmeyer Bernd , Lukevics Edmunds
Published: May 2005

1H, 13C, 15N, 29Si and 119Sn NMR data (chemical shifts and coupling constants) are reported for the organometallic substituted enamines Me3Sn(Me3M)CC(NEt2)CH2OMe [M = Sn (1), Ge (2), Si (3)], of which 2 and 3 are obtained as a mixture of E and Z isomers, and (Me3Sn)2CC(NEt2)CCNEt2. Since there is no inverse linear relationship between δ13C(MC) and δ15N, NC(pp)π interactions must be regarded as being very weak. All vicinal coupling constants, 3J(119Sn13C), 3J(119Sn15N) and 3J(29Si15N), across the CC double bond show the expected stereochemical dependence, with | 3Jtrans | > | 3Jcis |. To our knowledge, long‐range couplings of this type, involving 15N, are reported for the first time. The magnitude of | 3J(119Sn15N)trans | exceeds the magnitude of | 1J(119Sn15N) | in most trimethyltin amides. A relationship between the magnitude of | 3J(119Sn15N) | and the orientation of the nitrogen lone electron pair is proposed.
Sites of protonation in cardiotonic polyazaindolizines by NMR spectroscopy
Authors: Barraclough Paul , Firmin David , Lindon John C. , Nobbs Malcolm S. , Sanderson Paul N. , Smith Steven , Gillam Janet M.
Published: May 2005

The pKa, values of six sulmazole analogues were measured spectrophotometrically. The major protonation sites for most of these bridgehead nitrogen heterocycles were determined by 1H and 13C NMR methods. The aryl‐substituted imidazo[1,2‐a]pyrimidine (4), 8‐methoxyimidazo[1,2‐a]pyrazine (6), imidazo[1,2‐b]pyridazine (9) and imidazo[1,2‐b][1,2,4]triazine (11) undergo protonation at the imidazo nitrogen. The imidazo[1,2‐a]pyrazine (5) protonates mainly at N‐7. In some cases differences in basicity properties between these aryl analogues and the bridgehead heterocycles have been observed.
Application of deuteriated isotopomers in the analysis of 13C CP/MAS NMR spectra of some azo dyes
Authors: Straka Jaroslav , Schneider Bohdan , Lyčka Antonín , Jirman Josef
Published: May 2005

13C CP/MAS NMR spectra (50.3 MHz) of 4‐[N,N‐bis(2‐hydroxyethyl)amino]azobenzene (1), (N,N‐dimethylamino)azobenzene (2), 4‐methoxyazobenzene (3), 2‐hydroxy‐5‐tert‐butylazobenzene (4) and 4‐hydroxyazobenzene (5) were recorded. The isotopomers of 1, 4 and 5 with pentadeuteriated unsubstituted aromatic rings were also studied. Dipolar dephased spectra of the deuteriated isotopomers were used for chemical shift interpretation in the solid state. The changes in cross‐polarization dynamics caused by deuteration were investigated for 1. The spectra of 1, 2, 3, and 5 were also measured at elevated temperature. It was found that in 1, 2 and 5, rotation of the aromatic rings is induced at elevated temperature.
Conformational analysis of 5,6,7‐trisubstituted flavones: 13C NMR and molecular mechanics study
Authors: Biekofsky Rodolfo R. , Buschi Carlos A. , Pomilio Alicia B.
Published: May 2005

13C NMR spectra of six flavones from Gomphrena martiana were analysed and compared with those of two related flavones isolated from Popowia cauliflora. This series of compounds has a similar substitution pattern on ring A, all compounds having oxygenated substituents on C‐5, C‐6 and C‐7. Consistent trends in relating conformation to substituent chemical shift effects (SCS) were found by analysing the 13C NMR data for these compounds. Chemical shifts for ring A carbons were calculated using the principle of additivity of substituents and by taking into account the conformation of the substituents. A reasonable agreement between the calculated shifts and the experimental values was found. A molecular mechanics study of these compounds was undertaken in order to obtain a set of consistent molecular structures to search for correlations between molecular structure and measured 13C chemical shifts. Good agreement was found between the predicted molecular mechanics conformations and the 13C NMR spectral data.
New β‐dihydroagarofuran sesquiterpenoids from Celastrus paniculatus
Authors: Sang Hong , Wang Hanqing , Tu Yongqiang , Chen Yaozu
Published: May 2005

Two new β‐dihydroagarofuran sesquiterpene polyesters were isolated from Celastrus paniculatus. The structures were deduced using various 2D NMR techniques (HH COSY, CH COSY, COLOC, NOESY), NOE difference spectra and mass spectra. The positions of the ester moieties were located by 2D heteronuclear correlated spectra via long‐range coupling, or combined with NOE experiments. Their stereochemical structures were studied and the complete assignments of the 1H and 13C chemical shifts were made.
NMR study of thermodynamic and structural properties of molecular complexes formed by metalloporphyrins and aromatic substrates
Authors: Kitaigorodski Alexander N. , Edlund Ulf
Published: May 2005

1H NMR shifts and 13C spin–lattice relaxation rates were measured for various aromatic π‐acceptors (S) in solutions containing paramagnetic cobalt(II) and iron(III) porphyrins (P). The stability constants of P · S molecular complexes and limiting values of substrate chemical shifts in the complexes were determined from the concentration dependence of chemical shifts. The abilities of different substituents to promote complexation of aromatics with metalloporphyrins are discussed. The preferred substrate orientation in molecular complexes were derived using relative values of chemical shifts and relaxation rates induced by metalloporphyrins. Both monocyclic (benzene and pyridine derivatives) and bicyclic (naphthalene derivative) substrates tend to form ‘axially symmetric’ adducts with parallel π‐planes and the centre of the aromatic system situated in the vicinity of the porphyrin z‐axis.
High‐field magnetic resonance studies oftert‐butanol in liquid and solid phases
Authors: Aksnes D. W. , Kimtys L. L.
Published: May 2005

1H and13C line widths and1H,2H,13C and17O spin–lattice relaxation (times (T1) oftert‐butanol (TB) were studied at a field strength of 9.4 T in the liquid and solid states (160–299 K). The NMR line width data reveal the existence of at least two crystalline forms between 160 K and the metling point (299 K). The ordered phase (solid II) is observed throughout the whole temperature region on warming, indicating that the disordered phase (solid I), observed betweenca. 210 K and the melting point, is monotropic. The line narrowing of the1H resonances for solid I, observed around 225 and 280 K, is ascribed to the onset of overall molecular tumbling and translational diffusion, respectively. The1H line width of solid II is constant between 160 and 284 K. Activation parameters for the overall molecular tumbling and/or internal methyl andtert‐butyl reorientations were obtained from theT1data. The long correlation time (75–92 ps at the melting point) and high activation energy (27–37 kJ mol−1) suggest that the overall tumbling in the disordered and liquid phases involves hydrogen‐bonded aggregates. The dynamics of the methyl group, in contrast to thetert‐butyl group, appear to be only slightly affected by change of state and phase (activation energy 11–12 kJ mol−1).
Dynamic nuclear magnetic resonance of zinc and cadmium complexes of 1,2‐propanediaminetetraacetic acid
Authors: Li Fei , Song Ruifang
Published: May 2005

The 1H NMR temperature dependence of the zinc(II) and cadmium(II) complexes of 1,2‐propanediaminetetraacetic acid (1,2‐PDTA) was investigated. The four AB patterns in the 1H NMR spectra of the acetates of the complexes were assigned with the aid of computer‐simulated spectra at various temperatures. The AB interchange phenomena due to nitrogen inversion were observed in the temperature range 90–148°C. The rate constants and the activation parameters were calculated. It is shown that the nitrogen‐inversion rates of the two asymmetric nitrogen atoms are different, both for Zn(1,2‐PDTA)2− and for Cd(1,2‐PDTA)2−, and that those of the nitrogen atom on the same side as the methyl group are slower. A water displacement mechanism in the process of nitrogen inversion is proposed on the basis of the kinetic data.
13C‐selective, 1H‐detected 2D {1H, 13C} correlation spectra of oligosaccharides
Authors: Poppe Leszek , van Halbeek Herman
Published: May 2005

Two‐dimensional 1H‐detected {1H, 13C} shift correlation spectra of oligosaccharides usually suffer from low resolution in the 13C frequency domain. This drawback can be overcome through a simple modification of the HSQC experiment, namely by implementing a selective 13C 180° pulse. It is illustrated for the mixture of the α‐and β‐anomers of the trisaccharide sialyl‐α(2→6)‐lactose that 13C‐selective HSQC allows both one‐bond and multiple‐bond {1H, 13C} correlation spectra to be obtained with high resolution in the 13C domain.
Coordination‐site exchange and solid‐state 13C NMR studies of bis(oxalato)dioxovanadate(V) ion
Authors: Lee Man‐Ho , Schaumburg Kjeld
Published: May 2005

Activation parameters were determined for the exchange between the two types of carboxylate groups which are cis and trans to the VO bonds in the bis(oxalato)dioxovanadate(V) ion, [VO2(C2O4)2]3−. Kinetic data were obtained from the 13C NMR spectra at eleven temperatures between 268 and 306 K by the total line‐shape method. The coordination‐site exchange mechanism, involving chelate ring opening and closing in the ion, is proposed. The solid‐state 13C NMR spectra of the oxalato complexes, (NH4)3[VO2(C2O4)2]·2H2O and K3[VO2(C2O4)2]·3H2O, are also discussed in relation to the structures.
1H NMR determination of the ionization constant of a carboxylic acid group of a haem protein in mixed aqueous‐organic solvents using the super WEFT sequence
Authors: Rigby Stephen E. J. , Burch Anita M. , Moore Geoffrey R.
Published: May 2005

1H NMR spectra of ferricytochrome c‐551 were obtained in a variety of miscible aqueous buffer‐organic solvent mixtures. The pKa of a haem carboxyl group within this protein was measured in several such solvent systems. This work was facilitated by the use of the Super water eliminated Fourier transform (SuperWEFT) technique and this was extended to the suppression of multiple solvent resonances. Nuclear Overhauser enhancement difference experiments were combined with SuperWEFT, enabling structural data to be obtained in complex solvent mixtures. The data arising from this study are relevant to the evaluation and simulation of electrostatic effects in proteins.
Compounds with bridgehead nitrogen 66—NMR spectra and stereochemistry of derivatives of 1,2,3,4,6,7,12,12b‐ octahydropyrimido [1′, 6′:1,2] pyrido [3,4‐b]indol‐2‐one and of 1,3,4,6,7,11b‐hexahydropyrimido [6,1‐a] isoquinolin‐2‐one
Authors: Crabb Trevor A. , Patel Asmita V.
Published: May 2005

Comparison of the NMR spectra of 3‐methyl‐1,2,3,4,6,7,12,12b‐octahydropyrimido [1′,6′ : 1,2]pyrido[3,4‐b] indol‐2‐one and of cis‐(H‐6, H‐12b)‐3,6‐dimethyl‐ 1,2,3,4,6,7,12,12b‐octahydropyrimido [1′,6′:1,2]pyrido[3,4‐b] indol‐2‐one shows the former to exist in solution at 25°C as an equilibrium mixture containing ca. 20% N‐inside‐cis‐ and ca. 80% trans‐fused conformers, and the latter to adopt exclusively the trans‐fused conformer. The related 3‐methyl‐ 1,3,4,6,7,11b‐ hexahydropyrimido [6,1‐a] isoquinoline‐2‐one adopts a ca. 53% trans‐fused 47% cis‐fused equilibrium.
Isolation and structural elucidation of griffithine by 1D and 2D NMR techniques
Authors: Atta‐ur‐Rahman  , Pervin Azra , Feroz M. , Perveen Shahnaz , Choudhary M. I. , Hasan Naim
Published: May 2005

The isolation and structure elucidation of a novel dimeric alkaloid, griffithine, from the leafy shoots of Sophora griffithii Stock (Papilionaceae) is described. The alkaloid possesses a 12‐membered ring system formed by the linking of C‐10 and C‐10′ of the alkaloid with the N‐1 and N‐1′ atoms, respectively. The structure was established on the basis of extensive 1D and 2D NMR studies. The relative stereochemistry at the chiral centres was determined by NOE difference experiments. 10‐Oxosparteine was isolated for the first time from the leafy shoots of Sophora griffithii.
Magnetic moment determination of micro‐sized solid samples by proton magnetic resonance spectroscopy. A new split peak which can be used to determine the magnetic susceptibility of solid micro samples
Authors: Furuhashi Akiko , Ono Isao , Yamasaki Akira
Published: May 2005

The magnetic moment of a micro‐sized solid sample can be semi‐quantitatively determined by proton magnetic resonance spectral measurement with the sample in a capillary cell coaxially placed within an NMR tube containing a suitable diamagnetic solvent with a standard such as TMS. Small signals appearing on the low‐frequency side of the main peaks can be assigned to the protons in the layer of the solution surrounding the outer surface of the coaxially placed capillary. The molar chemical shift difference of this signal splitting is proportional to the square of the magnetic moment (μ) or n(n + 2), where n is equal to the number of unpaired electrons in the sample.
Liquid‐ and solid‐state (CP‐MAS) multinuclear magnetic resonance study of some 2,5‐dihydro‐1,2,5‐oxoniastannaboratoles—carboncarbon coupling constants, 1J(13C13C), in organometallic‐substituted alkenes
Authors: Wrackmeyer Bernd , Wagner Klaus , Sebald Angelika , Merwin Lawrence H. , Boese Roland
Published: May 2005

Derivatives of 2,5‐dihydro‐1,2,5‐oxoniastannaboratoles were studied by multinuclear magnetic resonance both in the liquid (11B, 13C, 29Si, 119Sn NMR) and solid state (13C, 29Si, 119Sn CP/MAS NMR). Together with the results of the x‐ray analysis of the 4,5,5‐triethyl‐2,5‐dihydro‐1,2,2‐trimethyl‐3‐phenyl‐1,2,5‐oxoniastannaboratole‐tetrahydrofuran adduct (1‐THF) (space group P21/c) the NMR data [chemical shifts and coupling constants J(119SnE) (E = 13C, 29Si, 119Sn)] allowed the assessment of structural features in solution and in the solid state (e.g. the weakened coordinative Sn‐O interactions in 1‐THF in solution). The 1J(13C13C) values in 4,5,5‐triethyl‐2,5‐dihydro‐1,2,2‐trimethyl‐3‐trimethylsilyl‐ and ‐3‐trimethylstannyl‐1,2,5‐oxoniastannaboratole and in some non‐cyclic alkenes bearing organometallic substituents were measured using INEPT experiments based on 3J(13C1H) long‐range coupling constants. In the presence of one boryl‐ and two stannyl groups the magnitude of 1J(13C13C) values is reduced to ca. 30 Hz. A positive sign for 2J(119Sn117Sn) in 2‐diethylboryl‐1,1‐bis(trimethylstannyl)but‐1‐ene was determined by 2D 13C1H and 2D 119Sn‐H heteronuclear shift correlations. Scalar 13C11B and 119Sn‐11B coupling has been observed for the first time in 119Sn CP‐MAS NMR spectra.
119Sn NMR study of organotin compounds having intramolecular Sn—N coordination
Authors: Jastrzebski Johann T. B. H. , Grove David M. , Boersma J. , van Koten Gerard , Ernsting Jan‐Meine
Published: May 2005

119Sn NMR data are reported for organotin compounds containing potentially C,N‐chelating ligands capable of forming five‐ or six‐membered chelate rings. The 119Sn chemical shifts of divalent organotin compounds containing such a ligand are found at relatively high frequency. Intramolecular coordination in tetraorganotin compounds has little influence on their 119Sn chemical shifts. However, additional coordination in tri‐ and di‐organotin halides causes a large shift to lower frequency of about 100 ppm. Finally, for organotin compounds which exist as a diastereoisomeric mixture in solution, two well resolved 119Sn resonances are observed.
Detection of connectivity between equivalent carbons in a C2 molecule using isotopomeric asymmetry: Identification of hopeaphenol in Carex pumila
Authors: Kawabata Jun , Fukushi Eri , Hara Masato , Mizutani Junya
Published: May 2005

In the structure determination of the C2 symmetrical tetrastilbene hopeaphenol, isolated from Carex pumila, the elucidation of the C‐‐C connectivity between equivalent carbons was needed. From an isotopomeric point of view, three isotopomers, 12C12C, 12C13C and 13C13C, are present with respect to the equivalent carbons connecting each other. Among them, the the 12C12C species is undetectable and the 13C13C species is excluded owing to its low natural abundance. Therefore, only the 12C13C isotopomer is detected in 13C NMR and this species is not symmetrical. In the H12C13H system, the separate detection of 1J(CH) and 2J(CH) was achieved by the INEPT‐LSPD, COLOC and HMBC methods to demonstrate the connectivity between the equivalent carbons from the viewpoint of isotopomeric asymmetry.
Heterocyclic compounds from sugars. XIV—Structure determination and conformational analysis of the four diastereoisomeric methyl 3‐Acetyl‐5,5‐dimethyl‐2‐(D‐galacto‐pentaacetoxypentyl)‐1,3‐thiazolidine‐4‐carboxylate 1‐Oxides
Authors: Kövér Katalin E. , Györgydeàk Zoltàn
Published: May 2005

1H and 13C NMR experiments were performed to analyse the conformation and stereochemistry of diastereomeric sulphoxides of 1,3‐thiazolidine derivatives. The conformation of the thiazolidine ring was verified by an NOE study. ASIS and 13C chemical shift data supported the sulphoxide configuration.
Quantification of partial structures in aquatic humic substances by volume integration of two‐dimensional 13C nuclear magnetic resonance spectra. Comparison of one‐ and two‐dimensional techniques
Authors: Lambert J. , Burba P. , Buddrus J.
Published: May 2005

Partial structures of a reference groundwater humic substance were quantified by J‐resolved two‐dimensional 13C NMR spectroscopy applied in its phase‐sensitive variant. The results agree with those obtained by the one‐dimensional techniques DEPT (distortionless enhancement by polarization transfer) and SEMUT‐90 (subspectral editing using a multiple quantum trap), thus demonstrating the accuracy of both methods. However, the two‐dimensional technique is recommended, because quantification is based on only one spectrum. Quantification provides the ratio of different substructures (carbons belonging to ketones, carboxylic acids, different aromatics, carbohydrates, paraffinic C, CH, CH2 and CH3 groups) and, in combination with elemental analysis, the partition of hydrogen between C and O (83% bonded to C and 17% to O). Also, insight is obtained into the biogenesis of the humic acids. Aromatic moieties probably originate mainly from lignin rather than from other aromatic compounds. CHO moieties mainly belong to carbons in ethers and alcohols and only to a small extent to carbons in carbohydrates, as shown by comparing NMR results with gas chromatographic analysis of the carbohydrate part performed by other workers. The ratio of paraffinic CH:CH2:CH3 is about 1:1:1; the high proportion of paraffinic methyl groups cannot yet be explained.
13C magic angle spinning NMR investigations of thiourea inclusion compounds
Authors: Müller Klaus
Published: May 2005

Thiourea inclusion compounds of three monosubstituted cyclohexanes were studied by 13C magic angle spinning NMR spectroscopy. Variable‐temperature experiments were performed to evaluate the conformational and motional features of the various guest molecules. From a quantitative line‐shape analysis it is found that the halocyclohexanes with chloro and bromo substituents exist predominantly in the axial conformation whereas methylcyclohexane, as in solution, prefers the equatorial position. Generally, it could be shown that within the temperature range investigated the cyclohexane guest molecules undergo ring inversion processes with kinetic parameters almost unaffected by the host lattice.
Microcomputer prediction and assessment of substituted benzene 13C NMR chemical shifts
Authors: Hearmon Richard Angus , Liu Hok‐Ming , Laverick Simon , Tayler Paul
Published: May 2005

A 13C NMR chemical shift prediction and spectral assessment program was written in Turbo Prolog. Based on the large data compendium of Ewing it allows the rapid assessment of the spectral–structural relationship for substituted benzene rings.
17O NMR spectra of the 1,6‐anhydro‐β‐D‐hexopyranoses and related‐compounds. Determination of configurational effects on the chemical shifts
Authors: Lauterwein Jürgen , Schulte Jürgen , Schumacher Martin , Černý Miloslav
Published: May 2005

Well resolved natural‐abundance 17O NMR spectra of the eight 1,6‐anhydro‐β‐D‐hexopyranoses and three deoxy model compounds were recorded in aqueous solution at 90°C. The assignment of the resonances was obtained by chemical shift comparison, O‐acetylation, lanthanide shift reagents (Eu3+) and, more generally applicable, by a computational search for the minimum of the sum of the squared deviations between the observed and calculated shifts. The 17O chemical shifts were evaluated depending on the orientation of the hydroxyl groups, expressed in terms of additive γ‐ and δ‐interactions between the hydroxyl and ring ether groups. The γ‐gauche effects were dominant in a range between −7 and −20 ppm. No appreciable effects have been detected of anti‐periplanar hydroxyl groups on the 17O chemical shifts. The syn‐diaxial δ‐interaction was deshielding between hydroxyl groups, but shielding between a hydroxyl group and the bridge‐ether oxygen. A new type of interaction, a δ‐effect between equatorial hydroxyl oxygens in a planar zig‐zag arrangement, was detected. Arguments are presented suggesting that γ‐gauche effects between oxygens are not related to steric compression.
Inverse detection of broad resonances: 15N NMR spectra of boron–nitrogen compounds
Authors: Wrackmeyer Bernd , Kupče Ēriks , Köster Roland , Seidel Günter
Published: May 2005

Two types of proton‐detected 1H15N correlation experiments were compared with respect to the observation of 15N NMR resonances broadened by scalar relaxation of the second kind. Both single‐ and multiple‐quantum experiments gave equal 15N line widths in F1, and in all cases the inverse experiments provided a dramatic increase in sensitivity and spectrometer time‐saving compared with the direct observation of 15N resonances. Various aminoboranes [B(NHMe)3; B(NHNMe2)3; 2,3‐dihydro‐2‐methyl‐2‐boraperimidine; organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles; organo‐substituted 7,8‐benzo‐1‐oxa‐6‐aza‐2‐sila‐5‐bora‐3‐cyclooctene], organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboratolates, an amine–borane adduct (organo‐substituted 7,8‐benzo‐6‐oxa‐1‐aza‐2‐sila‐5‐borabicyclo[3.3.0]oct‐3‐ene), and (ligand)transition metal π‐complexes of organo‐substituted 2,5‐dihydro‐1,2,5‐azasilaboroles were studied by two‐dimensional inverse 1H{15N} NMR experiments. The straightforward application to the analysis of several mixtures suggests that this technique is promising for the investigation of oligomerization and polymerization of boron—nitrogen compounds.
Variable‐temperature high‐resolution carbon‐13 studies of molecular motion in solid bisphenol‐F diglycidyl ether
Authors: Casarini Daniele , Harris Robin K. , Kenwright Alan M.
Published: May 2005

Variable‐temperature cross‐polarization magic‐angle spinning solid‐state 13C NMR spectra of bisphenol‐F diglycidyl ether were obtained in the temperature range 25–67°C. Dynamic phenomena are observed, and the experimental data are in accord with an inhomogeneous distribution of correlation times, perhaps related to a second‐order phase change. Single‐pulse excitation experiments under comparable conditions confirmed the presence of motional inhomogeneity, characterized by a fraction of mobile molecules within the sample. Differential scanning calorimetric measurements revealed a phase transition at ca. 50 °C.
Atropisomerism of 1‐alkylcyclohepta [b]pyrrol‐2(1H)‐ones. Isolation of the rotational isomers of 1‐(2,4‐dimethyl‐3‐pentyl)cyclohepta [b]pyrrol‐2(1H)‐one
Authors: Ikeda Yukari , Kato Nobuo , Mori Akira , Takeshita Hitoshi
Published: May 2005

1‐Alkylcyclohepta[b]pyrrol‐2(1H)‐ones showed rotational isomerism around the CN bond. Two rotamers of the 1‐(2,4‐dimethyl‐3‐pentyl) derivative were isolable by high‐performance liquid chromatography at 0°C. The activation free energy, measured by the line‐shape analysis of the variable‐temperature NMR spectra, was 86.8 kJ mol−1 at 25°C. In a bromo derivative, a positive buttressing effect was observed.
New Pt …︁ HN bonds characterized by 15N‐filtered and 2D NOESY 1H NMR spectroscopy
Authors: Pregosin Paul S. , Rüegger Heinz , Wombacher Franz , Van Koten Gerard , Grove David M. , Wehman‐Ooyevaar Ingrid C. M.
Published: May 2005

New Pt …︁ HN bonding modes in two cycloplatinated complexes, [Pt(C6H4CH2NMe2‐2‐C,N)(C6H4CH2NMe2H‐2‐C,H)Br] (1) and [Pt(1‐C10H6NMe2‐8‐C,N)(1‐C10H6NMe2H‐8‐C,H)Br] (2), were characterized by 15N‐filtered and 2D NOESY 1H measurements. Both 1 and 2 show markedly different interactions of an RNMe2H+ group with a platinum centre; the 1J(15N,1H) values of 69 and 59 Hz for 1 and 2, respectively, are considerably less than those of the related free and protonated organic amine systems. The corresponding 1J(195Pt,1H) values are 72 and 180 Hz, respectively. An approach both to understanding and recognizing these Pt …︁ HN interactions is presented.
Demonstration of bicontinuous structures in microemulsions using automatic‐mode NMR (self‐)diffusion measurements
Authors: Datema K. P. , Bolt‐Westerhoff J. A. , Jaspers A. , Daane J. G. R. , Rupert L. A. M.
Published: May 2005

The specifications of an NMR instrument dedicated to frequency‐resolved automated Fourier transform pulsed‐field‐gradient proton NMR measurements are reported. In order to be able also to monitor accurately the slow diffusion of surfactant aggregates and polymers in automatic mode, an option for matching of the gradient pulses was developed and implemented. In a first application, the spectrometer was used to carry out NMR (self‐) diffusion measurements of microemulsions of the surfactant sodium p‐(7‐tetradecyl)benzenesulphonate in benzene and water. They indicate drastic changes in the morphology of the aggregates in the microemulsion on increasing the surfactant concentration. The aggregate morphology changes from a bicontinuous structure to hard, noninteracting spheres by increasing the surfactant concentration in the microemulsion. The bicontinuous structure, i.e. a solution which is continuous in both water and oil, is the result of a strong interaction between the microemulsion droplets (‘percolation phenomenon’). It appears that the water molecules inside the microemulsion droplets with the hard sphere character exchange rapidly, on the (NMR) time scale of 10–100 ms, with water which is dissolved in the benzene. The droplets have an apparent diameter of 56 Å.
Conformational equilibria of ephedrine and pseudoephedrine and hydrogen bonding
Authors: Tsai Helen , Roberts John D.
Published: May 2005

Proton NMR spectra suggest that the conformation with trans vicinal hydrogens is favored for ephedrine as the free base in deuterium oxide, although in non‐polar solvents, such as deuteriotrichloromethane, the gauche vicinal hydrogen conformations are favored, as has been reported previously. The conjugate acid has primarily gauche hydrogens. In contrast, the trans‐hydrogen rotamers of pseudoephedrine dominate for both the non‐protonated and protonated forms in deuterium oxide. Hydrogen bonding is unlikely to be as important as usually assumed in determining the conformational preferences of these substances.
Organometallic paramagnetic camphor complexes. EPR investigation of their formation and structures
Authors: Rebmann Andreas , Mäurer Manfred , Scheffler Klaus , Stegmann Hartmut B.
Published: May 2005

Photochemical reactions of camphor and other diones with carbonylmanganese or aryltin compounds lead to paramagnetic complexes. The radicals derived from Mn2(CO)10 and Mn2(CO)8(PR3)2 are formulated as sixcoordinate complexes with different structures depending on the organic moiety, and they are characterized by their EPR and ENDOR data. Under the same conditions, the tin compounds form five‐coordinate complexes in which the organic ligand occupies one equatorial and one axial position in the bipyramidal structure. Consequently, two permutation isomers are expected if camphor quinone is used as a scavenger for the photolytically generated tin radicals, independent of the structure of the trapped species. These two species can be detected by ENDOR and triple resonance experiments if the interconversion is slow with respect to the EPR time scale. Diastereomeric complexes are obtained by the formation of a second chiral centre, at the tin atom, in the course of the reaction. However, these isomers cannot be distinguished by ENDOR spectroscopy under the conditions applied.
1H and 13C NMR study of novel fused 1,2,4‐triazole heterocycles
Authors: Szabó Zoltán , Kóródi Ferenc , Batta Gyula
Published: May 2005

The 1H and 13C NMR spectra of some novel 1,2,4‐triazolo [1,3] thiazinoquinoline isomeric pairs are interpreted in terms of structural assignments. The structure of most compounds has been confirmed by NOE difference spectroscopy. Characteristic differences have been observed in both 1H and 13C NMR spectra of these isomeric Pairs: some of the 1H and 13C chemical shifts, and also the one bond 13C1H couplings of triazole protons, differ consistently in the NMR spectra of the isomers. The coupling constants have been determined using a combination of INEPT and chemical shift selective filtering.
Complete assignment of the 1H and 13C NMR spectra of 8‐hydroxy‐7‐methoxy‐4‐methyl‐1α,4α,4aα,8β,8aα‐tetrahydro‐1,4‐methanonaphthalen‐5(1H)‐one
Authors: Minter David E. , Marchand Alar P. , Lu Shao‐Po
Published: May 2005

Diels–Alder cycloaddition of a mixture of 1‐ and 2‐methylcyclopentadienes (1a and 1b, respectively) to 2‐methoxy‐p‐benzoquinone (2) gave a mixture of isomeric endo [4 + 2] cycloadducts (3a–3d). Fractional recrystallization of this product mixture from EtOAc‐hexane gave 6‐methoxy‐1‐methyl‐1α,4α,4aα,8aα‐tetrahydro‐1,4‐methanonaphthalene‐5,8‐dione (3a). Reaction of 3a with NaBH4 in the presence of cerium(III) chloride resulted in the selective reduction of the less hindered CO group in 3a, thereby affording 8‐hydroxy‐7‐methoxy‐4‐methyl‐1α,4α,4aα,8β,8aα‐tetrahydro‐1,4‐methanonaphthalen‐5(1H)‐one (4). The 1H and 13C NMR spectra of 4, a novel tricyclic ketoalcohol, have been completely assigned by using a combination of one‐ and two‐dimensional NMR techniques.
13C NMR study of 1‐substituted imidazoles
Authors: Benedini Francesca , Ferrario Francesco , Sala Alberto
Published: May 2005

The 13C NMR spectra of a series of 1‐substituted imidazoles were measured and assigned on the basis of substituent chemical shifts and 13C/1H shift correlated spectra.
1H and 13C NMR spectra of some 2‐substituted 4,5‐dimethylfurans
Authors: Dandárová Miloslava , Végh Daniel
Published: May 2005

1H and 13C NMR spectra of 22 2‐substituted 4,5‐dimethylfurans are reported. The J(C, H) values were used for signal assignments and for the identification of geometrical isomers of some derivatives.
Solid‐state 31P NMR investigations of unsaturated phosphorus–nitrogen–sulfur rings
Authors: Chivers Tristram , Edwards Mark , Fyfe Colin A. , Randall Leslie H.
Published: May 2005

Solid‐state CP/MAS 31P NMR spectra were measured for the following unsaturated phosphorus–nitrogen–sulfur ring systems: 1,5‐R4P2N4S2 (R = Me, Et, Ph), 1,5‐Ph4P2N4S2Ph2, Ph2PN4S3NPPh3 and Ph2PN3S2. The isotropic solid‐state shifts correlate well with the corresponding shifts in solution, the largest difference being 9.0 ppm, indicating that there are no phase‐dependent structural features. Analysis of the principal elements of the shielding tensor by the spinning side band method showed that one of these elements is primarily responsible for the anomalously low‐field isotropic chemical shifts of 1,5‐R4P2N4S2, but no correlation was found between this individual tensor component and any of the structural parameters of these folded eight‐membered rings. Two isotropic shifts were observed for the crystallographically inequivalent phosphorus atoms of 1,5‐Et4P2N4S2, but the individual 31P isotropic shifts of 1,5‐Me4P2N4S2 were not resolved.
Simultaneous measurement of one‐bond and long‐range carbon–carbon coupling constants in cembrene
Authors: Ma L. , Bigler P.
Published: May 2005

A 1D pulse sequence designed for the selective detection of carbon–carbon connectivities and the measurement of the corresponding coupling constants is presented. The sequence takes advantage of the increased sensitivity and the higher accuracy obtained with multiselective excitation and 1D detection, respectively. The sequence is shown to be a valuable alternative to the popular 2D INADEQUATE experiment in cases where parts, instead of the full, carbon–carbon connectivity matrix are of interest. The sequence is especially useful for the selective measurement of the stereochemically interesting long‐range coupling constants.
Assignment of the 1H and 13C NMR spectra and conformational analysis of the pyrrolizidine alkaloid 13‐O‐acetyldicrotaline
Authors: Rycroft David S. , Stirling Iain R. , Robins David J.
Published: May 2005

The 1H and 13C NMR spectra of the pyrrolizidine alkaloid 13‐O‐acetyldicrotaline were studied at 4.7 T. A full assignment of the 1H and 13C signals was achieved by application of a variety of NMR techniques, including homonuclear 1H NOE difference, 2D δH/δH phase‐sensitive COSY and δC/δH direct and long‐range correlation experiments. The stereochemistry at C‐13 in dicrotaline is confirmed to be S, and the conformation of the elevenmembered macrocycle is compared with that of related pyrrolizidine alkaloids.
Characterization of oligosaccharides from the non‐reducing termini of keratan sulphate chains
Authors: Huckerby Thomas N. , Dickenson John M. , Nieduszynski Ian A.
Published: May 2005

Keratan sulphate (KS) chains prepared from both bovine tracheal rings and bovine femoral head cartilage were digested with the enzyme keratanase from Pseudomonas species and non‐reducing terminal oligosaccharides were fractionated and purified using high‐performance ion‐exchange chromatography. Two oligosaccharides were fully characterized using one‐ and two‐dimensional NMR spectroscopic methods. An oligosaccharide derived from bovine tracheal ring KS chains was shown to have the structure NeuAcα2–3Galβ1–4GlcNAc(6‐SO4)β1–3Gal(6‐SO4)β1–4GlcNAc(6‐SO4)β1–3Gal‐ol (1). An oligosaccharide derived from bovine articular cartilage after treatment with a keratanase preparation containing neuraminidase activity was shown to have the structure Galβ1–4GlcNAc(6‐SO4)β1–3Gal(6‐SO4)β1–4GlcNAc(6‐SO4)β1–3Gal‐ol (2). These non‐reducing terminal structures are KS chain caps or terminators which, because of their accessibility, are likely to be involved in interactions with other macromolecules of the extracellular matrix.
NMR spectroscopy of paramagnetic complexes. Part 39—natural abundance 2H NMR of paramagnetic sandwich compounds
Authors: Blümel Janet , Hofmann Peter , Köhler Frank H.
Published: May 2005

The methylated metallocenes (MeCp)2M with M = V, Cr, Mn, Co, Ni (1–5) were investigated by 1H and 2H NMR spectroscopy at natural abundance. The 2H NMR signals are narrower by a factor of up to 30 compared with the corresponding 1H NMR signals, thus establishing an inexpensive method and a general improvement of the NMR spectra of paramagnetic π‐complexes. This has allowed the resolution of the signal splitting of Cp deuterons of 1 and 5 which could not be observed earlier in the 1H NMR spectra. The origin of the small (1 and 5) and large (2–4) signal splittings is discussed and related to an extended Hückel calculation. The relative magnitude of the signal splitting is reproduced, but the signal assignment had to be deduced from 13C NMR results. Primary isotope shifts of up to 4.0 ppm were found for 1, 2, 4 and 5. The much higher values for 3 (up to 16.6 ppm) reflect the combined influence of the intrinsic isotope shift and the isotope effect on the spin crossover.
Substituent effects on deuterium isotope effects on nuclear shielding of intramolecularly hydrogen‐bonded aromatic ketones, aldehydes and esters
Authors: Hansen Poul Erik
Published: May 2005

Deuterium isotope effects on 13C nuclear shielding, nΔC(OD), were investigated for a large number of substituted ortho‐substituted aromatic hydroxyacyl compounds of the type salicylaldehyde, 2‐hydroxyacetophenone, etc. The isotope effects were analysed as a function of substitution patterns. 2ΔC‐2(OD) shows a linear dependence on ΔOH, with one slope for 4‐ and 6‐substituted derivatives and another for 5‐substituted derivatives. A similar pattern is also found for the long range isotope effects. In addition, isotope effects also correlate with 13C chemical shifts. Isotope effects in o‐hydroxyacetophenones can be predicted from the δOH and nΔC(OD) values of salicylaldehyde, and vice versa. The isotope effects were analysed in terms of a vibrational term related to the intramolecular hydrogen bond and an electronic term related to the substituent influence on the transmission of the effect along the pathway between the deuterium‐substituted oxygen and the carbon in question. 2ΔC(OD) isotope effects are found to depend on the one‐bond bond order of the CC bond of the unsubstituted hydrocarbons. Long‐range isotope effects are observed to the olefinic carbons of 2‐hydroxychalcone, whereas no effects beyond C‐1′ are seen in o‐hydroxyketones or o‐hydroxybenzophenones. The tautomeric equilibrium of usnic acid is perturbed by the removal of the weak hydrogen bond between 9‐OH and the carbonyl group at C‐1.
Effect of the ortho‐nitro group on the 13C NMR chemical shifts of substituted pyridines
Authors: Rasala Danuta , Gawinecki Ryszard
Published: May 2005

The 13C NMR spectra of 40 vicinally substituted 2‐ and 3‐nitropyridines were recorded. The observed chemical shifts are, in general, non‐additive. These results are discussed in terms of the effects of 2‐, 3‐ and 4‐substitutents on the ring carbons and of the position of the fixed nitro group and the substituent. The chemical shifts of the para carbon, with respect to the substitutent, follow well the dual substituent parameter approach, which shows their electronic origin. However, the substituent chemical shifts of both ipso and ortho positions can be rationalized, in terms of multiple parameter substituent correlation analysis, only on a approximate level.
NMR spectra and stereochemistry of 6‐ and 7‐substituted cyclopenta [d][1,3]dioxanes
Authors: Crabb Trevor A. , Porssa Manuchehr , Patel Asmita V. , Elmore Norman F.
Published: May 2005

The reaction between 6‐ and 7‐ketocyclopenta[d] [1,3]dioxane and methyl‐phenylmagnesium bromide gave in each case only one isomer of the 6‐hydroxy‐6‐methyl‐phenyl‐ and 7‐hydroxy‐7‐methyl‐phenylcyclopenta [d] [1,3]dioxanes. The configurations of these derivatives were determined from a detailed analysis of the 1H NMR spectra. All the compounds were found to adopt the O‐inside cis‐fused conformations.
Assignment of the configuration of a substituent in saturated six‐membered ring compounds using the 13C chemical shifts of a single epimer
Authors: Pandiarajan K. , Manimekalai A.
Published: May 2005

The possibility of assigning the configuration of a substituent in six‐membered ring compounds from the 13C chemical shifts of a single epimer was examined. The chemical shifts of the ring carbons in saturated six‐membered ring compounds were calculated using standard substituent parameters obtained from tert‐butyl systems, and these calculated values were compared with the observed values. It was found that in isomeric 1,3‐ and 1,4‐disubstituted cyclohexanes the configuration could be assigned correctly for each isomer by comparing the observed chemical shifts with the calculated values, an exception being trans‐1,3‐dihydroxycyclohexane. However, in the 1,2‐disubstituted cyclohexanes the configuration could be assigned correctly only by comparing the observed and calculated chemical shifts for the γ‐ or β‐methylene carbons. The configuration cannot be assigned correctly in heterocyclic systems by using the individual chemical shifts as probes. However, when the sum of the chemical shifts of the ring carbons could be calculated for equatorial and axial orientations of the substituent using standard substituent parameters to a reasonable degree of accuracy, the configuration for any epimer could be assigned correctly by comparing the observed and calculated sums.
13C NMR of pyrazoles
Authors: Begtrup Mikael , Boyer Gérard , Cabildo Pilar , Cativiela Carlos , Claramunt Rosa M. , Elguero José , García José Ignacio , Toiron Catherine , Vedsø Per
Published: May 2005

The carbon‐13 chemical shifts and coupling constants of 1168 pyrazoles are reported, some of them in several solvents. These data are briefly discussed on the basis of statistical treatment and qualitative comparisons.
Isogambogic acid and isomorellinol from Garcinia hanburyi
Authors: Lin Lee‐Juian , Lin Long‐Ze , Pezzuto John M. , Cordell Geoffrey A. , Ruangrungsi Nijsiri
Published: May 2005

Three xanthone derivatives, gambogic acid, isogambogic acid and isomorellinol, were isolated from the dried latex of Garcinia hanburyi. Two of them, isogambogic acid and isomorellinol, are new. Determinations of the structures and stereochemistry were achieved independently by a series of NMR experiments including COSY, ROESY, HMQC, HMBC and selective INEPT. Isolation of isomorellinol from G. hanburyi provided important chemical evidence to link this species to G. morella. The presence of gambogic acid and isogambogic acid, however, demonstrated the difference between these two species. Cytotoxic evaluation of these isolates revealed that all three were active against KB and drug‐resistant KB‐V1 cell lines.
Theoretical study of the γ‐gauche effect for an n‐paraffin by using an ab initio GIAO–CHF procedure
Authors: Kurosu Hiromichi , Ando Isao , Webb Graham A.
Published: May 2005

Ab initio 13C nuclear shielding calculations of the γ‐gauche effect for an n‐paraffin using the GIAO–CHF procedure are reported. The geometrical parameters used are optimized for each dihedral angle. The dihedral angle dependences of shielding constant calculations are carried out and the γ‐gauche effect on n‐octane is discussed.
Temperature effects on the 1H1H, 1H19F and 1919F coupling constants of fluorobenzene and 1,2‐difluorobenzene
Authors: Suntioinen Sirpa , Weber Ursula , Laatikainen Reino
Published: May 2005

The 1H NMR spectra of fluorobenzene and 1,2‐difluorobenzene were measured in acetonitrile‐d3 and cyclohexane‐d12 at four temperatures to study the temperature dependence of 1H1H, 1H19F and 19F19F coupling constants. In acetonitrile‐d3 the 5J(F,H) coupling constant of fluorobenzene decreases by 5%, the 5J(H,H) coupling increases by 0.5% and all other couplings decrease by less than 1% when the temperature increases from 283 to 333 K. In cyclohexane‐d12 the change in 5J(F,H) for fluorobenzene is much smaller than in acetonitrile‐d6; the other changes are normally slightly smaller than in acetonitrile‐d5. The changes for 1,2‐difluorobenzene are generally of the same order as those for fluorobenzene.
Structural studies on mesoionic 1,2,3,4‐thiatriazolo‐5‐aminides and 1,2,3,4‐thiatriazolo‐5‐methylides by nitrogen and carbon NMR
Authors: Jażwiński Jaroslaw , Stefaniak Lech
Published: May 2005

15N, 14N, 13C and 1H NMR data were used for the structural analysis of seven 1,2,3,4‐thiatriazoles with various exocyclic groups. Measurements at various temperatures were carried out in order to study the behaviour of exocyclic groups. Some 15N‐labelled compounds were prepared to assist in the interpretation of the 15N NMR spectra. The results suggest that the investigated compounds exist in the cyclic structure. Three of the investigated compounds have not been previously synthesized.
Synthesis, EPR, ENDOR and TRIPLE resonance investigations of anthracycline‐related semiquinones
Authors: Stegmann Hartmut B. , Jülich Thomas , Höfler Ulrike , Schuler Paul , Koch Wolfhard , Krohn Karsten , Eickhoff Astrid
Published: May 2005

The synthesis of five substituted anthraquinones related to anthracyclines is described. One‐electron reduction of these compounds yields the corresponding semiquinones, which were characterized by EPR, ENDOR and TRIPLE resonance spectroscopy. The data indicate a rapid conformational interconversion of the cyclohexene moiety (ring A in the anthracyclines). The low‐temperature structures could be assigned to half‐chair conformers whose splitting constants and torsion angles were obtained by simple calculations. Introduction of substituents in the 4‐position, disturbing the symmetry of the anthraquinone, results in remarkable changes in the spin density distribution, in contrast to published results. A reinterpretation and assignment of known anthraquinone radicals is presented.
Motional heterogeneity and polymorphism of bisphenol‐A diacetate
Authors: Casarini Daniele , Harris Robin K. , Kenwright Alan M.
Published: May 2005

Two polymorphs of bisphenol‐A diacetate [2,2‐bis(p‐acetoxyphenyl)propane] were characterized by solid‐state 13C cross‐polarization magic‐angle spinning NMR, X‐ray powder diffraction and differential scanning calorimetic measurements. The structure of one polymorph was determined by single‐crystal x‐ray diffraction methods, and shown to have two molecules in the asymmetric unit. The two polymorphs show markedly different molecular mobilities, as reflected in variable‐temperature solid‐state NMR measurements, with one polymorph exhibiting motional heterogeneity in the flipping of the phenylene rings.
Complete 1H and 13C NMR spectral assignment of pentacyclo [6.4.0.02,6.05,9.04,12]dodecane derivatives and structure elucidation of pentacyclo [6.4.0.02,6.03,11.05,9]dodecane
Authors: Martins F. J. C. , Coetzee G. H. , Fourie L. , Venter H. J. , Viljoen A. M. , Wessels P. L.
Published: May 2005

Treatment of pentacyclo[6.4.0.02,6.05,9.04,12]dodecane‐2‐ol with concentrated sulphuric acid produced the rearranged hydrocarbon pentacyclo[6.4.0.02,6.03,11.05,9]dodecane as the main product. High‐field 1H and 13C NMR techniques were used in the structure elucidation and assignment of the different NMR resonances of these two and related compounds.