bluuebunny/crossref_metadata_2025_split huggingface dataset:
15N NMR spectroscopy 24—chemical shifts and coupling constants of α‐amino acid N‐carboxyanhydrides and related heterocycles
Authors: Kricheldorf Hans R. 
Published: May 2005

AbstractThe chemical shifts of amino acid N‐carboxyanhydrides (NCAs) and cyclic or linear urethanes are less sensitive to solvent effects than those of amides and lactams. The values of the one‐bond 15N1H coupling constants depend on the solvent and are 5‐8 Hz larger than those of ureas and amides. The 15N13C coupling constant of the NCO group is also unusually high, while that of the N—CH group lies within the range known for N‐acylated aliphatic amines. The one‐bond 15N13C coupling constant was found to be insensitive to conformational changes.
Stereochemical studies—XXXVII: Saturated heterocycles—XIII Configuration and conformation of Z‐ and E‐N‐methyl‐ and ‐N‐ benzyl‐2‐p‐nitrophenyl‐4,5‐ and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines
Authors: Sohár P. , Gera L. , Bernáth G. 
Published: May 2005

AbstractThe configuration and conformation of Z‐ and E‐N‐methyl‐ and ‐N‐benzyl‐2‐p‐nitrophenyl‐4,5‐, and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines were determined by 1H and 13C NMR spectroscopy. The Z isomers were proved to be conformationally homogeneous, having the heteroatom in axial and equatorial position, respectively, in the case of the 5,6‐ and 4,5‐tetramethylene compounds. Consequently, the p‐nitrophenyl group and the anellated cyclohexyl ring are all‐cis arranged in the Z‐5,6‐tetramethylene compounds while in the case of the Z‐4,5‐tetramethylene isomers the p‐nitrophenyl group and the cyclohexyl ring are trans arranged to the hetero ring.
Determination of the isotope distribution in partially deuterated compounds by NMR difference spectroscopy
Authors: Roth K. , Melzer P. , Kurreck H. 
Published: May 2005

AbstractThe position and the isotope distribution within labelled compounds can be determined by NMR by analysing the difference spectrum, and its integral, of the labelled and the corresponding parent compound. The method is applied to m‐terphenyl and it 4–4″‐dideutero derivative.
The structure and ring‐puckering vibration of thietane as studied by 1H and 13C NMR spectra of the oriented molecule
Authors: Jokisaari J. , Kuonanoja J. , Häkkinen A.‐M. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of partially oriented thietane have been recorded and analysed. The molecular structure was determined assuming the molecule to be planar and rigid. Because of the unsatisfactory fit of the dipolar coupling constants, a model which also takes into account the ring‐puckering vibration was applied. This model leads to a better fit, but also to long CH distances. Consequently, it seems that the one‐dimensional ring‐puckering model does not on its own explain the differences between the experimental and calculated coupling constants.
Proton magnetic resonance spectra of substituted adamantane‐2,4‐diones. Determination of the C‐6 and C‐9 stereochemistry
Authors: Ahmed S. Asghari , Hickmott Peter W. , Cooper Maurice W. , Stenhouse Ian A. 
Published: May 2005

AbstractThe 220 MHz 1H NMR spectra of 6‐hydroxy‐7‐methyl‐6‐phenyladamantane‐2,4‐dione, 6‐hydroxy‐5,7‐dimethyl‐6‐phenyladamantane‐2,4‐dione, and 6‐hydroxy‐7,9‐dimethyl‐6‐phenyladamantane‐2,4‐dione have been determined and complete proton assignments carried out with the aid of multiple irradiation. The stereochemistry of the C‐6 and C‐9 chiral centres have been determined and some of the factors affecting the magnitude of the geminal, vicinal and W coupling constants are discussed.
Carbon‐13 NMR studies on some 5‐substituted quinoxalines
Authors: Hollstein Ulrich , Krisov Galen E. 
Published: May 2005

AbstractEleven 5‐substituted quinoxalines (NO2, NH2, COOH, OCH3, CH3, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their 13C NMR spectra have been measured in DMSO‐d6 and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1‐substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1‐substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5‐Fluoroquinoxaline was also measured in CDCl3, CD3COCD3, CD3CN, CD3OD, C6D6 and CD3COOD. In all solvents an abnormally low 2J(CF) (∼ 12 Hz) was found for C‐4a and no CF spin‐spin splitting could be detected for the three‐bond coupling of C‐8a. Similar abnormalities were found in 2‐fluoroaniline and 2‐fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C‐8 (‘para’ position) and the Hammett σp parameter of the substituent.
A carbon‐13 nuclear magnetic resonance study of compounds substituted by a perfluoroalkyl chain
Authors: Tordeux M. , Leroy J. , Wakselman C. 
Published: May 2005

AbstractThe 13C NMR spectra of alkanes, alkanones and cyclohexanones substituted by perfluoroalkyl groups, RF, have been studied. The influence of the perfluoroalkyl group on the chemical shifts of other carbons of the molecules is the same regardless of the RF chain length.
1H and 13C NMR of substituted chromium tricarbonyl complexes; substituent effects and Cr(CO3) conformation
Authors: Solladié‐Cavallo A. , Suffert J. 
Published: May 2005

AbstractIt is shown that 13C NMR is not suitable for determining the conformation of the Cr(CO)3 group in monosubstituted chromium tricarbonyl complexes. However,. 1H NMR can be used for such determinations if one takes substituent effects into account, whn necessary, and an appropriate relationship is proposed. The populations, xA, of the eclipsed conformer so obtained for various substituents increase with the π donor ability of the substituent. These results are consistent with X‐ray results and with Carter and Hoffmann's models.
Carbon‐13 nuclear magnetic resonance studies of leonurine hydrochloride and its analogues
Authors: Langford Gordon E. , Yates Peter , Yeung Hin Wing , Cheng Kin Fai 
Published: May 2005

AbstractThe 13C NMR spectra of leonurine hydrochloride and thirteen of its analogues in DMSO‐d6 have been analyzed. Changes in the aromatic substituents have no significant effect on the chemical shifts of the side chain methylene carbons indicating that they do not influence the conformation of the latter. Observed deviations from additivity of substituent effects for the methylene carbon chemical shifts suggest that the methylene side chains of these compounds may be more tightly coiled than are the corresponding n‐alkanes. In representative cases no change in conformation is evident in 50% aqueous DMSO‐d6 solutions, indicating that similar considerations may apply in aqueous media.
Structure determination of di‐O‐benzylidene derivatives of L‐iditol by 1H and 13C NMR spectroscopy
Authors: Sohár P. , Fehér G. , Toldy L. 
Published: May 2005

AbstractThe configuration and stable conformation of two dibenzylidene‐L‐iditol isomers formed upon benzalation of L‐iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative—the main product of the benzalation reaction—were determined by 1H and 13C NMR spectroscopy.
The nuclear magnetic resonance spectra of N‐nitroso‐N‐alkyl amino acids
Authors: Chow Yuan L. , Polo Joel 
Published: May 2005

AbstractStructurally related acyclic and cyclic N‐nitroso‐N‐alkyl amino acids were prepared and their 1H, 13C and 15N NMR spectra were investigated. The changes in the 13C NMR spectra of the N‐nitroso α‐amino acids after dissolving in solvents suggest that they posses the Z‐configuration in the crystalline state; in solution some of them isomerize to mixtures of the Z‐ and E‐isomers whose composition appear to depend on steric factors. The 13C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The 13C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the α‐carbons and shielding on the β‐carbons.
A carbon‐13 NMR study of phenyl‐substituted cyclophosphazenes
Authors: Krishnamurthy S. S. , Ramabrahmam P. , Woods M. 
Published: May 2005

AbstractThe 13C NMR spectra of the cyclotriphosphazenes N3P3CI6−n Phn (n=2, 3, 4, 6) and the tetrameric derivatives 2,2,6,6‐N4P4CI4Ph4 and N4P4Ph8 have been recorded. The carbon chemical shifts can be largely explained on the basis of concomitant mesomeric electron release from the benzene ring and inductive electron withdrawal by phosphorus. The magnitude of 1J(P, C‐1) for the non‐geminal compounds is ≃40 Hz higher than that observed for the geminal compounds. Some aspects of the NMR data are also discussed with reference to the X‐ray crystal structures of several phenyl‐substituted cyclotri‐ and cyclotetra‐phosphazenes.
Coupling of chromatography and NMR. 3—study of flowing gas chromatographic fractions by proton magnetic resonance
Authors: Buddrus Joachim , Herzog Helmut 
Published: May 2005

AbstractA procedure is described which allows the recording of 1H NMR spectra from gas chromatographic (GC) fractions flowing through the magnetic field with a velocity of c. 0.6 cm/s. The spectra are obtained by the pulse Fourier transform technique; the beginning and the termination of the pulse sequence is timed according to the chromatogram from a thermal conductivity detector. The line width of the signals in the NMR spectra is 2 Hz.
Tritium nuclear magnetic resonance spectroscopy. 14—analysis of tritiated methyl groups
Authors: Bloxsidge James P. , Elvidge John A. , Jones John R. , Evans E. Anthony , Kitcher J. Philip , Warrell David C. 
Published: May 2005

AbstractThe complete analysis of the tritium distribution in tritiated methyl groups in labelled compounds is achieved by a direct method for the first time, through 3H NMR spectroscopy aided by resolution enhancement.
1H and 13C NMR study of 8‐hydroxyquinoline and some of its 5‐substituted analogues
Authors: Kidrič J. , Hadži D. , Kocjan D. , Rutar V. 
Published: May 2005

Abstract1H and 13C NMR spectra of 8‐hydroxyquinoline (oxine) and its 5‐Me, 5‐F, 5‐Cl, 5‐Br and 5‐NO2 derivatives have been studied in DMSO‐d6 solution. The 1H and 13C chemical shifts and proton–proton, proton–fluorine, carbon–proton and carbon–fluorine coupling constants have been determined. The 1H and 13C chemical shifts have been correlated with the charge densities on the hydrogen and carbon atoms calculated by the CNDO/2 method. The correlation of the 1H and 13C chemical shifts with the total charge densities on the carbon atoms is approximately linear (rH2 = 0.85, rC2 = 0.84). The proton in peri position to the nitro group in 5‐NO2‐oxine is an exception.
Synthesis, 1H NMR spectral properties and conformational preferences of some open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units
Authors: Bottino Francesco , Pappalardo Sebastiano 
Published: May 2005

AbstractThe conformational preferences in solution of eight new open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units have been investigated, parallel to those of some structurally related phenyl sulphides, by means of 1H NMR spectroscopy. The results obtained have shown that replacement of phenyl by the pyridyl or the 1,3,4‐thiadiazolyl moieties induces slightly different propeller arrangements, ascribed to the higher conjugative tendency of both electron‐deficient heteroaromatic rings, in all open‐chain mixed sulphides, in opposition to the skew arrangements observed for phenyl sulphide derivatives. No prominent differences have been found for cyclic sulphides, which preferentially adopt the sterically unhindered saddle shape conformation.
NMR study of the structure of the nitration intermediate of furfural
Authors: Gaset A. , Gorrichon J. P. 
Published: May 2005

AbstractThe structure of the intermediate obtained in the come of the nitrationof 2‐furancarboxaldehyde was investigated by means of1H and13C NMR. It was shown unambiguously that this intermediate is 2‐acetoxy‐2‐diacetogymethyl‐5‐nitro‐2,5‐dihydrofuran.
Proton polarization transfer in natural abundance 15N NMR studies of E‐ and Z‐isomers of N‐alkylformamides
Authors: Sørensen O. W. , Scheibye S. , Lawesson S.‐O. , Jakobsen H. J. 
Published: May 2005

AbstractProton polarization transfer has been used for the convenient observation of proton coupled natural abundance 15N NMR spectra of the E‐ and Z‐isomers of N‐methylformamide at 10.14 MHz. Second‐order spectral analysis is required to determine the 15NH coupling constants, at least for the E‐isomer of secondary formamides. An useful stereospecificity is observed for both the one‐ and two‐bond 15NH coupling constants.
The assignment of the 1H and the 13C NMR chemical shifts of N‐phenyl‐2,4‐dimethylbuta‐1,3‐diene‐1,4‐sultam
Authors: Radeglia R. , Fanghänel E. 
Published: May 2005

AbstractThe assignment of the signals in the 13C and 1H NMR spectra of N‐phenyl‐2,4‐dimethylbuta‐1,3‐diene‐1,4‐sultam is difficult for the signal pairs C‐2 and C‐4, C‐1 and C‐3, (C‐1)H, (C‐2)CH3 and (C‐4)CH3. The 13C NMR spectrum recorded under gated decoupling conditions provide long‐range couplings which make possible an unambiguous assignment of the 13C NMR signal pairs. Application of the 1H CW off‐resonance decoupling technique in recording the 13C NMR spectra enables the assignment information from the 13C NMR spectrum to be transferred to the 1H NMR spectrum.
Mercury‐199 NMR chemical shifts in substituted diphenylmercury and phenylmercuric chloride
Authors: Wells Peter R. , Hawker Darryl W. 
Published: May 2005

AbstractThe influence of substituents on the 199Hg chemical shifts of some Ar2Hg and ArHgCl species in 1:1 CDCl3: CH2Cl2 and in CDCl3: DMSO solutions is reported. The effects are substantial and are in the direction of electron withdrawal producing increased shielding (i.e. shifts towards higher field).
Dihedral‐angle dependence of the vicinal 15N,13C spin‐coupling constants. A new NMR parameter for the conformational analysis of amino acids and peptides
Authors: Kainosho Masatsune , Tsuji Takashi 
Published: May 2005

AbstractThe first successful observation of the vicinal 15N,13C spin‐coupling constants in a series of amino acids, comprising Val, Ile, Leu and Thr, in which the α‐nitrogens are fully replaced with 15N, is described. A Karplus‐type dihedral‐angle dependence was noted for the coupling constants between the α‐nitrogen and γ‐carbon nuclei which may, in turn, be applied to the conformational analysis of other amino acids and small peptides. The potential usefulness and limitation of this new parameter in such applications is briefly discussed.
Carbon‐13 T1 measurements on glyceryl trivalerate
Authors: Hosur Ramakrishna V. , Govil Girjesh 
Published: May 2005

Abstract13C spin lattice relaxation times (T1) of glyceryl trivalerate have been measured as a function of concentration in CDCl3 solutions. The T1 values indicate that there is a gradient in the rate of rotational motions around the CC bonds in the hydrocarbon chains, the rate increasing towards the methyl groups. Examination of T1 values as a function of concentration suggests that glyceryl trivalerate does not aggregate in CDCl3 solutions, unlike other lipids with long hydrocarbon chains. It is concluded that the length of the hydrocarbon chain plays a dominant role in determining the aggregation behaviour of lipids in solution.
Carbon‐13 nuclear magnetic resonance study of the motional behaviour of bilirubin and of some of its derivatives
Authors: Kaplan Doron , Navon Gil 
Published: May 2005

AbstractA comparative study of the spin‐lattice relaxation times (T1) of proton‐bearing carbons in bilirubin and its derivatives is reported. The NT1 values of the backbone carbons indicate that the overall reorientation of the molecule is isotropic. In dimethyl sulphoxide solutions, the segmental motion of the propionic side chains is very limited in bilirubin, bilirubin dimethyl ester and mesobilirubin dimethyl ester, faster in dimethoxybilirubin dimethyl ester and is very fast in the propionic residue of vinylneoxanthobilirubinic acid methyl ester. The relative mobilities of the propionic residues are interpreted on the basis of intramolecular hydrogen bonding in which the solvent participates. The dimeric form of bilirubin dimethyl ester in chloroform solutions is confirmed by the correlation time of tumbling of the backbone. In this solvent the segmental motion of the propionic side chains is rapid, indicating the probable absence of hydrogen‐bonding. In bilirubin, bilirubin dimethyl ester and dimethoxybilirubin dimethyl ester, internal rotation is rapid for the endo‐vinyl group and slow for the exo group, correlating with reported differences in the chemical behaviour of these residues in bile pigments.
The structural dependence of two‐bond 13C13C coupling constants
Authors: Klessinger Martin , Stöcker Michael 
Published: May 2005

AbstractTwo‐bond 13C13C coupling constants are discussed on the basis of INDO‐SCPT calculations. The dependence of 2J(CC) on bond angle variation and on methyl substitution is evaluated, and it is shown that 2J(CC) depends linearly on the bond orbital s‐character product of the terminal carbon atoms, whereas no systematic relationship with the hybridization of the central carbon atom was obtained. Alkyl group substituent effects are found to be additive. The coupling constants of a number of cyclobutane derivatives are discussed on the basis of these structural relationships; it is shown that the experimental findings can be interpreted quite consistently by assuming a dual‐pathway coupling mechanism.
1H and 13C NMR study of the effects exerted by an oxirane ring in the epoxybicyclo‐[2.2.2]octane series
Authors: Christol H. , Laffite C. , Plénat F. , Renard G. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 2,3‐disubstituted exo‐5,6‐ and endo‐5,6‐bicyclo[2.2.2]octanes, and the corresponding alkanes, have been investigated to determine the effects exerted by an oxirane ring. The 1H NMR study showed that the anti protons, H‐7a and H‐8a, are significantly shielded and the syn protons, H‐7s and H‐8s, are deshielded, although to a smaller extent, by the exo‐oxirane. An endo‐oxirane has practically no effect on the same protons. The stereochemistry of epoxybicyclo[2.2.2]octanes is, thus, easily deduced from 1H NMR data. The 13C NMR study of the epoxy compounds provided an estimate of the value of α, β, γ syn and γ anti effects (to the epoxide oxygen) of an oxirane ring. In these rigid bicyclic molecules, of known geometry, the γ syn and the γ anti effects are of the same value, even though the dihedral angles are very different (0° and 120°).
ESR studies of nitroxide radicals formed in the low temperature photolysis of N‐nitrosamines
Authors: Joshi Avinash , Yang George C. 
Published: May 2005

AbstractVarious N‐nitrosamines were photolyzed in toluene solution in the temperature range −100°C to −30°C to yield dialkyl nitroxides. The nitrosamines studied were N‐nitrosodimethylamine, N‐nitrosodiethylamine, N‐nitrosodipropylamine, N‐nitrosodibutylamine and N‐nitrosodicyclohexylamine. Subsequent nitroxide side products were also detected by ESR, and a mechanism for their formation is proposed. Temperature dependent hyperfine couplings of the methylene protons were observed for a few radicals of the type R1CH2NO˙R2.
The effect of iodine on the carbon‐13 relaxation times of pyridine
Authors: Smith William B. 
Published: May 2005

AbstractThe addition of iodine to pyridine not only causes appreciable changes in the 13C chemical shifts but also a marked reduction in spin‐lattice relaxation times. The effect at the γ‐carbon is larger than at the α‐ and β‐carbons. This is consistent with the formation of a pyridine‐iodine complex with a preferential tumbling about the C‐γNI axis. Elementary theory is applied to approximate the tumbling ratio.
Carbon‐13 resonance assignments of some friedelanes and taraxasteranes
Authors: Patra Amarendra , Mukhopadhyay Apurba K. , Mitra Alok K. 
Published: May 2005

AbstractCarbon‐13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol and epi‐friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revision.
13C nuclear magnetic resonance spectra of several hydroxy diterpene derivatives
Authors: Delmond Bernard , Taran Martine , Valade Jacques , Petraud Michel , Barbe Bernard 
Published: May 2005

Abstract13C NMR spectra of several hydroxy diterpene derivatives having a pimarane, isopimarane and (13S, 8α)rosane skeleton have been recorded. The most significant effects caused by the introduction of hydroxyl groups in such a skeleton are demonstrated. The magnitudes of the γ‐ and δ‐effects are large enough to allow their use in sterochemical assignments.
1H NMR studies of 3,8‐dioxatricyclo‐[3.2.1.02,4]octane derivatives
Authors: Marfisi Claude , Cossu Michèle , Aycard Jean‐Pierre 
Published: May 2005

AbstractA series of 6‐X‐3,8‐dioxatricyclo[3.2.1.02,4]octanes (XCO2CH3, CN, Cl and CN) are studied by NMR, after their syntheses by epoxidation of the corresponding 7‐oxabicyclo[2.2.1]heptenes. The NMR parameters (J, δ) are determined, and also the anisotropy effects of methyl groups at the 1,5 bridgehead positions. The results allow an unambiguous identification of the diastereo‐isomers having a gem‐chlorocyano group in the 6 position.
13C chemical shifts of symmetrically substituted biphenyls: Unambiguous signal assignment for the carbons ortho and para to an aryl group
Authors: Fuji Karou , Yamada Toshihide , Fujita Eiichi 
Published: May 2005

AbstractThe natural abundance 13C NMR spectra of 2,2′‐dimethyl‐, 2,2′‐dimethoxy‐ and 2,2′‐dihydroxybiphenyls, and a series of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls were recorded. Unambiguous signal assignments of the carbons ortho and para to an aryl ring in biphenyls were made by selective deuteration and/or the graphical method for 1H single frequency off‐resonance decoupled spectra. Contrary to the reported assignments, it was shown that the signal for C‐6 in 2,2′‐dimethylbiphenyl clearly appears at lower field than that for C‐4. The signals for the ortho carbons (C‐6) of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls generally appeared at lower fields than those for the para carbons (C‐4). The validity of applying deuterium isotope shifts to the assignments of 13C chemical shifts of di‐ and tetra‐substituted biphenyls is also discussed.
Carbon‐13 NMR spin‐lattice relaxation in dithiarsolanes. Correlation between molecular motions and structural properties
Authors: Aksnes D. W. , Holak T. A. 
Published: May 2005

Abstract13C NMR spin‐lattice relaxation times (T1) and nuclear Overhauser enhancements (η) were measured for dithiarsolanes. The contributions of dipolar (T) and spin‐rotation (T) mechanisms were determined. The T1 data were analysed to obtain information on the relative order of magnitude of the internal motion rates. The calculations were based on the isotropic, with internal rotation about the AsPh bond, model of reorientation. In cis, trans‐2‐phenyl‐4‐methyl‐1,3,2‐dithiarsolane, the internal rotation of the phenyl ring is c. three times faster than overall molecular reorientation. The internal motion of the arsolane ring is slightly slower than the phenyl ring rotation. The rotation of the methyl groups in the compounds appears to be considerably hindered, with rotation energy barriers of c. 10 kJ mol−1. In contrast to the situation in the 4‐methyldithiarsolane, the internal motion of the arsolane ring is twice as fast as the internal rotation of the phenyl ring for the methyl‐unsubstituted analogue, 2‐phenyl‐1,3,2‐dithiarsolane.