bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractAn 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractSeveral 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

AbstractN‐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

AbstractKnown 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

AbstractThe 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.
High‐field NMR studies of tert‐butyl cyanide in liquid and solid phases
Authors: Aksnes Dagfinn W. , Kimtys Liudvikas L. , Ramstad Kari 
Published: May 2005

Abstract1H, 2H and 14N NMR line widths and spin—lattice relaxation times (T1) of tert‐butyl cyanide (TBCN) were measured at a field strength of 9.4 T in the liquid and solid states. The NMR line width data reveal the existence of two crystalline phases between 160 K and the melting point (292 K). The ordered phase (solid II) is observed throughout most of the temperature region on warming (170–290 K), indicating that the disordered phase (solid I), observed between ca 260 K and the melting point, is monotropic. The 1H line width of solid II is large and almost constant between 171 and 285 K (19–16 kHz), indicating slow whole‐molecule motion. The line narrowing of the 2H and 14N resonances observed above ca 260 K is ascribed to the onset of the whole‐molecule motion, slow overall molecular tumbling and fast C4 reorientations of the dipole axis. Activation parameters for the whole‐molecule motions and internal methyl and tert‐butyl reorientations (C3 and C3 motions, respectively) were obtained from the T1 data. The activation energy for the overall tumbling motion increases from 9.6 to 31 kJ mol−1 on freezing. This motion is very fast in the liquid (1.6 × 1012 s−1 at the melting point), but too slow to affect T1 in the solid phase. However, in solid I the molecular symmetry axis is also undergoing rapid, low‐amplitude reorientations with an activation energy of 8.9 kJ mol−1. The faster motion in solid II is the uniaxial C3′ reorientations with an activation energy of 15 kJ mol−1, while the slower motion is the C3 reorientation with an activation energy of 19 kJ mol−1.
Phosphorus 31P Spin–lattice relaxation times as a tool for the determination of the structure of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom
Authors: Mikolajczyk Marian , Wróblewski Krzysztof , Graczyk Piotr P. 
Published: May 2005

AbstractRelaxation times, T, due to the dipolar mechanism of relaxation of 31P nuclei were determined for eight pairs of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom. The separation of dipole–dipole from the total spin–lattice relaxation could be applied for the unambiguous assignment of configuration of the compounds under investigation. The T relaxation times are smaller for compounds with phosphorus located axially (cis). This observation is discussed in terms of internal rotation around the C‐2 bond and the distances between the phosphorus and axial H‐4,6 protons.
Studies on ferrocene derivatives. VIII—1H nuclear magnetic resonance studies of 1,1′‐bis(o‐hydroxyphenyl)ferrocene
Authors: Okada Yutaka , Hayashi Takatoshi 
Published: May 2005

AbstractIn 1,1′‐bis(substituted‐phenyl)ferrocenes the protons of the second cyclopentadienyl (Cp) group are influenced by the ring current effect of the Ph group bonded to the first Cp group. The conformations of these derivatives are discussed with respect to the anisotropy of the Ph groups. The chemical shifts of 1,1′‐bis(o‐hydroxphenyl)ferrocene were unrepresentative in comparison with the other ortho derivatives. Both an OHO and an OH d type hydrogen bond are formed in this derivative, so that the two Ph groups are adjacent in the preferred conformation.
Two‐dimensional NMR analysis of selected photochromic spiroindolinonaphthoxazines
Authors: Malatesta V. , Allegrini P. , Neri C. , Lanzini L. 
Published: May 2005

Abstract1H and 13C studies of a series of 19 photochromic spiroindolinonaphthoxazines were carried out by two‐dimensional NMR methods. The assignments of the 1H resonances were made by 2D homonuclear shift correlation (COSY) and the 2D nuclear Overhauser effect (NOESY). Complete 13C chemical shift assignments were carried out by using DEPT and two‐dimensional heteronuclear correlation spectroscopy.
Two‐dimensional NMR studies on the additivity rules for carbon‐13 chemical shifts in tetra‐n‐alkylammonium halides
Authors: Cheng Jinlong , Xenopoulos Alexander , Wunderlich Bernhard 
Published: May 2005

AbstractThe 13C chemical shifts of symmetric tetra‐n‐alkylammonium cations with n = 1–18 were identified unambiguously using two‐dimensional homonuclear (1H) chemical shift correlation (COSY) and heteronuclear (1H, 13C) chemical shift correlation spectroscopy (XHCORR). The 13C chemical shifts in small tetra‐n‐alkylammonium cations with less than five carbons in a chain are found to decrease from C‐1 (bonded to the nitrogen) (52‐60 ppm) to the methyl chain end (7‐14 ppm). For the cations with longer chains the values of chemical shifts are not in sequence with the carbon positions in an alkyl chain. The chemical shifts of C‐2 (22.5 ppm) are close to that of the methylene carbon next to the methyl group. The C‐3 carbon resonates at 26.4 ppm and is more shielded than the third carbon from the chain end (31.4 ppm). The chemical shifts of the remaining carbons are very similar to those of carbons in a corresponding linear alkane. The differences of the chemical shifts in alkylammonium salts from the corresponding n‐alkanes are largest for C‐1, C‐2 and C‐3, and this can be ascribed to the effects of the positive charge on C‐1, and the restricted segmental motion for the innermost region of the cations. Empirical additivity rules for the chemical shifts of C‐1, C‐2, and C‐3 are derived from the experimental results on 26 symmetric tetra‐n‐alkylammonium salts, and are tested for some asymmetrical systems with unequal chain lengths in the cation.
Quinazoline–iodine interaction as studied by NMR in nematic solutions
Authors: Suryaprakash N. , Khetrapal C. L. , Diehl P. 
Published: May 2005

AbstractThe results of an NMR study of the interaction of quinazoline with iodine in the nematic phase indicate the formation of at least two different types of charge‐transfer complexes. Significant changes in the molecular geometry of the quinazoline moiety were observed as a result of complexation with iodine. Detailed information on the formation of the charge‐transfer complexes was derived from the changes in the molecular structure, order parameters and chemical shifts as functions of iodine concentration. The observed changes in the order parameters are interpreted in terms of bond interaction tensors.
Conformation and dynamics in a solution of an N‐quaternized cinnamide derivative: A molecule active as a UV filter
Authors: Anselmi Cecilia , Centini Marisanna , Scotton Mirella , Sega Alessandro 
Published: May 2005

AbstractThe dynamics and conformation ofN,N‐dimethyl‐N‐[3‐(4‐methoxy‐trans‐cinnamoylamino)propyl]‐N‐n‐dodecylammonium bromide (1) have been established in two solvents (CDCl3 and DMSO‐d6) by the use of 13C spin–lattice relaxation rates, non‐selective and selective proton spin–lattice relaxation rates and 1H–(1H) NOE experiments. The two solvents affect the conformation of the cinnamide moiety in different ways. This alters the anchor capacity of the moiety towards the alkyl chain and, as a consequence, the dynamics of 1 in CDCl3 and DMSO‐d6 show understandable differences. However, the main mean conformations of 1 in both solvents are ‘linear’. The data do not allow the rationalization of the relationship between conformation and sunscreen efficiency.
η5‐Cyclopentadienyl derivatives of tin(II) studied by two‐dimensional multinuclear magnetic resonance in solution and by 13C and 119Sn CP/MAS NMR in the solid state
Authors: Wrackmeyer Bernd , Kupče Ēriks , Kehr Gerald , Sebald Angelika 
Published: May 2005

AbstractAbsolute coupling signs of 1J(119Sn, 13C) (<O) and 2J(119Sn, 1H) (<O) in (n5‐C5H5)2Sn (1) and 1J(119Sn, 13C) (<O)2J(119Sn, 13C) (<O) and 3J(119Sn, 1H) (>O) in (n5‐C5Me5)2Sn (2) were determined using advanced direct and indirect two‐dimensional methods. These are based on Ψ‐BIRD techniques and z‐filtering, leading to pseudotriple‐resonance experiments of the type 1H{119Sn(13C)} and 13C{1H(119Sn)}, respectively. A mixed n5‐cyclopentadienyltin(II) amide was prepared and characterized by 1H, 13C, 29Si and 119Sn NMR in solution in the presence of its symmetrical redistribution products 1 and [(Me3Si)2N]2Sn. Solid‐state 119Sn CP/MAS NMR spectra of 1 shows the presence of two tin sites (in accord with the x‐ray analysis) with a 62.2 ppm difference in 119Sn chemical shifts, the mean value being in close agreement with the solution‐state δ119Sn value. The symmetries of the shielding tensor for the two tin sites are different and there appears to be a correlation between this property and the ring centroid—Sn—ring centroid angle α. 13C CP/MAS NMR proved insensitive to the structural differences between the two types of molecules of 1 in the unit cell.
Structure establishment by two‐dimensional NMR spectroscopy of the product obtained in the reaction of MCPBA and himachalol and revised 1H NMR assignments for himachalol
Authors: Agrawal Pawan K. , Frahm August W. , Schneider M. 
Published: May 2005

AbstractThe reaction of himachalol with m‐chloroperoxybenzoic acid afforded a rearrangement product, the structure of which was deduced by 2D NMR analysis to be 3α,4α‐epoxyhimachalane‐2α,7α‐diol. The recently proposed 1H NMR assignments for himachalol have been revised, based on the analysis of 2D COSY, DEPT, HETCOR and NOE experiments.
Solution behaviour and redistribution reactions of tetraorganodistannoxane dimers
Authors: Jain Vimal K. , Mokal V. B. , Sandor P. 
Published: May 2005

AbstractThe solution behaviour and redistribution reactions of tetraorganodistannoxane dimers were investigated by 19F and 119Sn NMR spectroscopy. The variable‐temperature NMR data suggest that both the ‘ladder’ and ‘staircase’ structures exist in solution. Redistribution between two different tetrabutylstannoxanes is rapid on the NMR time scale. The 119Sn 2D EXSY NMR data for [Bu2Sn(F)OSnBu2(Cl)]2 indicate that there is no exchange between exo‐ and endocyclic tin centres.
NMR studies of hindered rotation and thermal decomposition of novel 1‐aryl‐3,3‐dialkyltriazenes
Authors: Lippert Th. , Wokaun A. , Dauth J. , Nuyken O. 
Published: May 2005

Abstract1‐Aryl‐3,3‐dialkyltriazenes have been synthesized by coupling the corresponding diazonium salts of substituted aniline derivatives with dialkylamines. The thermostability of these compounds was investigated by differential scanning calorimetry; activation energies of 240–280 kJ mol−1 were determined for the thermal decomposition. The hindered rotation of the dialkylamino group was studied by 1H NMR exchange measurements. Both experiments are interpreted in terms of an involvement of a 1,3‐dipolar structure of the NNN functional group. The influence of substituents, both on the aromatic ring and at the amino group, on the kinetic and activation parameters is investigated; results are analysed on the basis of mesomeric and steric effects on the dipolar charge distribution in the molecule.
1H and 13C NMR study of 2,3‐di‐ carboxymethyl‐7‐oxabicyclo[2.2.1]hepta‐2,5‐diene derivatives
Authors: Bighelli Ange , Tomi Félix , Casanova Joseph 
Published: May 2005

Abstract13C and 1H NMR spectral assignments have been obtained for 2,3‐di‐carboxymethyl‐ 7 ‐oxabicyclo[2.2.1]hepta‐ 2,5‐diene and 19 of its derivatives. The use of a combination of one‐dimensional and two‐dimensional NMR techniques allowed the unambiguous assignments of all 13C resonances of the bicyclic framework.
Coherent and incoherent magnetization transfer in the rotating frame
Authors: Hwang Tsang‐Lin , Kadkhodaei Mehran , Mohebbi Afsaneh , Shaka A. J. 
Published: May 2005

AbstractTwo‐dimensional (2D) NMR spectroscopy has become a routine part of molecular structure determination in liquids. In most modern experiments there is some correlation of transition frequencies between the two dimensions, and the mechanism responsible for the correlation dictates the information obtainable from the 2D spectrum. Two distinct mechanisms for magnetization transfer are considered: scalar coupling and cross‐relaxation. The former gives rise to information about the proximity of spins through the electronic framework of the molecule and the latter provides information on spatial proximity and molecular motion. Two‐dimensional experiments of both types are described, concentrating in particular on TOCSY and ROESY. It is shown how polarization transfer can be tailored and controlled, and how the unwanted coherent transfer due to J coupling can be eliminated in the ROESY experiment. Throughout the discussion, the multiple‐pulse sequence used for each experiment is the central focal point, and its design and analysis are the main considerations.
Comparative evaluation of conventional 5 mm inverse and micro inverse detection probes at 500 MHz
Authors: Crouch Ronald C. , Martin Gary E. 
Published: May 2005

AbstractPerformance and sensitivity characteristics of a standard 5 mm inverse detection probe and a new micro inverse detection probe design were compared on identical amounts of material at 500 MHz. The latter consistently afforded approximately twice the signal‐to‐noise performance of the former in two‐dimensional experiments, corresponding to a factor of four improvement in performance times to obtain comparable signal‐to‐noise ratio projections of HMQC data. The latter also facilitated the acquisition of HMQC spectra on much smaller amounts of material than was possible in the conventional 5 mm inverse detection probe.
Structure elucidation by NMR spectroscopy of saccharolidin A, a novel antiparasitic macrolide from Saccharothrix aerocolonigenes
Authors: Swanson Alistair G. , Monday Robert A. , Perry David A. 
Published: May 2005

AbstractThe structure of saccharolidin A, C38H60O9, a macrolide with antiparasitic properties isolated from Saccharothrix aerocolonigenes, was determined by two‐dimensional NMR using a fragment‐directed approach. Complete elucidation of the structure required concerted application of a range of homo‐ and heteronuclear experiments (TOCSY, ROESY, HMQC, HMBC, HMQC‐TOCSY). Saccharolidin A is related to the hygrolides but contains a number of unique features which distinguish it from previously reported members of this family. It is unsubstituted on C‐2 and contains both a 1,3‐dioxepane ring and an unsubstituted n‐pentyl side‐chain. The relative stereochemistry within each of the three groups of contiguous chiral centres has been determined.
Long‐range deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen‐bonded compounds. Purpurogallins
Authors: Hansen Poul Erik 
Published: May 2005

AbstractLong‐range deuterium isotope effects on 13C chemical shifts, nΔC(OD), were studied in the intramolecularly hydrogen‐bonded purpurogallins (benzotropolones). A very large long‐range isotope effect from the hydrogenbonded 4‐OH(D) is observed over six bonds at C‐7. Further, long‐range isotope effects are transmitted over as many as eight bonds. The transmission pathway including the carbonyl carbon is favoured, and some of the long‐range effects are transmitted via the carbonyl group. Large long‐range isotope effects are thus observed in hydrogen‐bonded systems with effective conjugation to the carbonyl group via alternating double bonds. This study indirectly supports recent theoretical predictions. The 13C and 1H NMR spectra of purpurogallin and its 2,3‐dimethyl, 2,3,6‐trimethyl and 2,3,4,6‐tetramethyl derivatives are assigned, and the hydrogen bond patterns are established based on the OH chemical shifts and 2ΔC(OD) isotope effects.
Determination and assignment of heteronuclear 119Sn1H coupling constants
Authors: Ratier Max , Jousseaume Bernard , Noiret Nicolas , Petit Nathalie , Lartigue Jean‐Claude , Pétraud Michel 
Published: May 2005

AbstractnJ(119Sn, 1H) coupling constants were determined by 2D 13C1H and 119Sn1H non‐refocused COLOC (TPPI) correlation methods. As the 2D 13C1H method only gives access to coupling constants directly measured from the spectra, the proposed non‐refocused COLOC technique is more general since it allows measurements in the case of satellites which are non‐observable in 13C NMR spectra. An optimization method for the τ value in COLOC experiments is also proposed.
13C and 17O NMR spectra of ketenes: A new and unusual type of heavy‐atom effect
Authors: Duddeck H. , Praas H.‐W. 
Published: May 2005

AbstractThe 13C and 17O chemical shifts of a number of ketenes are reported and discussed in terms of electronic and mesomeric substituent influences. New deshielding α‐ and shielding γ‐heavy‐atom effects are reported. The corresponding data for carboxylic acid bromides and chlorides are given.