bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid‐state NMR study of the kinetics of a ring chain tautomerism in a tetrahydro‐1, 3‐oxazine derivative
Authors: Riddell Frank G. , Rogerson Martin , Fülöp Ferenc , Bernáth Gábor
Published: May 2005

Condensation of cis‐2‐aminomethylcyclohexanol with p‐nitrobenzaldehyde under mild conditions initially gives the imine as the kinetically controlled product. The imine undergoes a solid‐state rearrangement to the bicyclic tetrahydro‐1, 3‐oxazine. The kinetics of the rearrangement were followed by solid‐state CP/MAS 13C NMR spectroscopy over the temperature range 283–297 K and the reaction was shown to have an activation energy of 85.0 ± 14.7 kJ mol−1. The probable reaction mechanism is discussed.
Ab initio 13C nuclear shielding calculations for some solid amino acids using the GIAO procedure
Authors: He Yong , Wu Donghui , Shen Lianfang , Li Baiwen , Webb Graham A.
Published: May 2005

The results of ab initio GIAO‐CHF 13C nuclear shielding calculations for some solid amino acids, performed with the 6—311G** and a locally dense basis set are reported. Comparison of the present calculation with the observed shieldings shows an RMS error of 6.6 ppm. Shieldings of the carbon nuclei which are multiply bonded are strongly influenced by electron correlation effects. Experimental molecular geometries used in these calculations were taken from crystal structures of amino acids.
1‐alkynyldioxaborolanes: Determination of 1J(13C,11B) from 13C NMR studies at 102°C
Authors: Cheesman Bruce Victor , Deloux Laurent , Srebnik Morris
Published: May 2005

Broad 13C resonances, as the result of partially relaxed scalar 13C11B coupling, were observed for the C‐1 and to a lesser extent C‐2 carbons of 1‐alkynyldioxaborolanes at 25°C. Measurement of the 13C spectra at 102°C resulted in a slower 11B quadrupolar relaxation rate and allowed the determination of 1J(13C,11B) scalar coupling from the resulting quadruplets for the C‐1 carbon.
Measurement of indirect spin—spin coupling constants between crystallographically equivalent nuclei. Determination of 2J(31P, 31P) in solid Ag[P(m‐tolyl)3]2NO3
Authors: Wu Gang , Wasylishen Roderick E. , Pan Hongjun , Liu C. W. , Fackler John P. , Shang Maoyu
Published: May 2005

Solid‐state 31P magic angle spinning (MAS) NMR spectra of Ag[P(m‐tolyl)3]2NO3 were investigated as a function of the magic angle spinning frequency. Examination of the 31P MAS NMR spectra obtained at 4.70 and 9.40 T indicates that the two phosphorus nuclei have identical isotropic chemical shifts, that is, they are crystallo‐graphically equivalent, δ = 11.2 ppm. However, since the orientation of their respective chemical shift tensors is not coincident, the two phosphorus nuclei are magnetically non‐equivalent and exhibit spinning‐frequency dependent 31P NMR lineshapes. Analysis of the spinning‐frequency dependent 31P MAS NMR spectra at 4.70 and 9.40 T indicates that 2J(31P, 31P) = 140 Hz. This value was confirmed by 2D J‐resolved spectroscopy. The determination of an indirect spin‐spin coupling constant between two nuclei which constitute an ‘isolated’ spin pair with identical isotropic chemical shifts is not possible in conventional solution‐state NMR studies unless a third spin is introduced. The 31P MAS NMR spectra of Ag[P(m‐tolyl)3]2NO3 also exhibit resolvable splittings due to 109Ag and 107Ag; 1J(109Ag, 31P) = 517±5 Hz and 1J(107Ag, 31P) = 453 ± 5 Hz. In solution NMR studies these couplings are not always observed because of rapid metal‐ligand exchange.
NMR assignments and absolute configuration of kauranoids
Authors: Tan R. X. , Wang W. Z. , Wu S. X. , Yang L.
Published: May 2005

A new ent‐kaurane diterpenoid glycoside has been shown to be the main sweetening constituent of the traditional medicines Aster tongolensis and A. ageratoides native to China. This study involved the total 1H and 13C spectral assignment of the compound and its degraded product by means of two‐dimensional NMR techniques (COSY, NOESY, HETCOR and TOCSY) and resulted in unambiguous spectral assignments, particularly in the heavily convoluted regions of the spectra. Concerning the absolute stereochemistry, the sweetener was determined to be (4R,5S,8S,9S,10,13R)‐16,17‐dihydroxykauran‐19‐oic acid β‐D‐glucopyranosyl ester through a combination of circular dichroism and 2D NMR techniques.
Rapid method for combined X—{1H} NOE and T1 measurement using heteronuclear polarization transfer
Authors: Kövér Katalin E. , Forgó Péter , Batta Gyula
Published: May 2005

A polarization transfer enhanced inversion‐recovery experiment is proposed for the combined measurement of heteronuclear T1 and NOE of low‐γ nuclei. This method offers significant time savings compared with conventional relaxation measurements. The reliability and accuracy of the combined T1, and NOE determination and its dependence on the experimental set‐up is also demonstrated. The proposed approach may be preferred for multiple field/multiple temperature model‐free analysis of molecular dynamics.
Analysis of 13C NMR substituent chemical shifts in some (aryl)(2‐nitrobenzo [b]thiophen‐3‐yl)amines: A new class of compounds with analgesic, anti‐exudative and anti‐inflammatory activities showing low mutagenicity
Authors: Lamartina Liliana , Spinelli Domenico , Guerrera Francesco , Sarvà Maria Concetta
Published: May 2005

The 13C NMR chemical shift values of (aryl)(2‐nitrobenzo[b]thiophen‐3‐yl)amines were measured in DMSO‐d6 solutions, suggesting the occurrence of an alternate charge polarization at C‐3, C‐2, C‐3a, C‐7a, C‐4 and C‐5. A dual substituent parameter analysis of the experimental data indicates a large or a low resonance contribution for aryl para or meta substituents, respectively, while the inductive component remains constant throughout.
Pure absorption phase gradient‐enhanced HMQC‐TOCSY with direct response editing
Authors: Crouch Ronald C. , Davis Ann O. , Martin Gary E.
Published: May 2005

Pulsed field gradients (PFG) have the potential to revolutionize further potent, inverse‐detected structural NMR techniques by eliminating artifacts and thermal noise in data taken with very small numbers of transients. A phase‐sensitive GE (gradient‐enhanced)‐HMQC‐TOCSY experiment is reported with features which allow the discrimination (or elimination) of direct correlations relative to the relayed TOCSY responses. Sensitivity losses which arise from molecular diffusion during the course of a pulse sequence are potentially serious when field gradients are employed for solutions containing small molecules. By carefully combining phase cycling with relatively weak pulsed field gradients, it is possible both to maintain good sensitivity and to suppress completely t1 noise in GE‐HMQC‐TOCSY data acquired with only two transients per t1, increment.
Solid state NMR investigations of dicalcium phosphates
Authors: Schaumburg K. , Shabanova E. , Eichner P.
Published: May 2005

Important new information about the crystal structure of dicalcium phosphate (DCP) powders was obtained using the 31P NMR technique. There were two types of powders under investigation. One type includes pure DA (CaHPO4) and DH (CaHPO4· 2H2O) powders, and their mixtures in different proportions. The other includes powders from an industrial production. They were obtained by DH heating. An effective and fast method of identification of the structure of the nuclear nearest surroundings is presented. Determination of the concentration of nearest surroundings corresponding to DA or DH types for the 31P nuclei was demonstrated on examples taken from production powders. Good agreement was found in comparison with data obtained by chemical analysis. Especially interesting information is obtained by using the CP MAS NMR technique. This method allows the following conclusions about the production sample structure to be drawn: it is a powder consisting of DH‐type microcrystals, but with numerous vacancies at the positions of water molecules which disappeared during heating.
103Rh chemical shifts and trans influence of ligands in rhodoximes and organorhodoximes
Authors: Ludwig M. , Öhrström L. , Steinborn D.
Published: May 2005

The 103Rh NMR chemical shifts of rhodoximes [Rh(dmgH)2(PPh3)X] (1) and organorhodoximes [Rh(dmgH)2(L)R] (2, L = PPh3; 3, L = PMe3; 4, L = P(OPh)3; 5, L = SMe2; 6, L = py) were measured with a wide range of anionic ligands X, organo groups R and axial ligands L. The chemical shifts δ(103Rh) in the halide complexes 1 show the ‘normal halogen dependence’ (Cl > Br > I). δ(103Rh) in 2–6 depends on the axial base L in the order py > SMe2 > PPh3 > P(OPh)3 ≈︁ PMe3 and in 2 on the organo group R in the order Et ≈︁ Me < nPr < CH2Ph ≈︁ CH2OMe < CH2Br < CH2Cl < iPr < Cy < CHCH2 < CH2SiMe3 < tBu < cis‐CHCHPh ≈︁ cis‐CHCHPr < Ph ≈︁ CCPh < CPrCH2. The coupling constants 1J(103Rh,31P) in 2 reflect the (NMR) trans influence of R. There is a strong correspondence between the NMR trans influence and the structural trans influence, as indicated by the bond lengths d(Rh—P).
4J(HH)‐Kopplungen in den 3‐Chlor‐2,3‐dibrombuttersäuremethylestern
Authors: Brink Maud
Published: May 2005

4J(HH)‐Kopplungen in die beiden stereoisomeren 3‐Chlor‐2,3‐dibrombuttersäuremethylester wurden in fünf Lösungsmitteln ermittelt.
Free radicals in the reactions of organic cations
Authors: Bubnov N. N. , Medvedev B. Ya. , Polyakova L. A. , Bilevich K. A. , Okhlobystin O. Yu.
Published: May 2005

By using the ESR and CIDNP methods the formation of free radicals in the reaction of nucleophilic and electrophilic substitution is proved. The role of free radicals in the mechanism of these reactions is discussed.
FT–NMR investigation of 13C11B coupling. A reappraisal
Authors: Axelson D. E. , Oliver A. J. , Holloway C. E.
Published: May 2005

An earlier short communication on this topic reports some incorrect 11B13C coupling parameters. The correct data are given together with some 10B coupling and isomer shift data.
Substituent effects in proton NMR of monosubstituted acetophenones: I
Authors: Caplin G. A.
Published: May 2005

Chemical shifts are reported for the acetyl protons in a series of para‐substituted acetophenones in a number of solvents, and substituent effects evaluated statistically by means of the Swain‐Lupton multiple correlation analysis. A basic set of substituents was built up by careful choice of substituted derivatives, and it was shown that this facilitated the possibility of valid comparisons of substituent effects between differing systems. Strong emphasis was placed on the idea of individuality of substituents and solvents.
Substituent chemical shift correlations. Hammett σp+ values and shifts for exocyclic protons in para‐substituted benzene derivatives
Authors: Lynch Brian Maurice
Published: May 2005

The methyl 1H NMR shifts for series of para‐substituted N,N‐dimethylanilines as their conjugate acids in trifluoroacetic acid, and series of para‐substituted N,N,N‐trimethylphenyl‐ammonium iodides in acetonitrile and in deuterium oxide, and the methylene shifts for series of para‐substituted N,N‐diethylanilines as their conjugate acids in deuteriosulfuric acid, are shown to be linearly related to the Hammett σp+ parameter. It is proposed that this dependence reflects a response of the chemical shift of the proton of the probe moiety to the electron density at the point of attachment of the probe to the aromatic ring and that this response is determined by the electric field effect of the charge at the point of attachment. Literature data are cited to indicate that Hammett σp+–1H NMR shift relationships may be general for probe moieties lacking a through‐resonance mechanism for interaction between the probe and the aromatic ring.
Carbon‐13 chemical shifts of some cholinergic neural transmission agents
Authors: Simeral Larry , Maciel Gary E.
Published: May 2005

Carbon‐13 chemical shifts have been obtained in the pulse Fourier transform mode on the following cholinergic neural transmission agents: acetylcholine, β‐methyl acetylcholine, carbamoyl choline, choline, tetramethylammonium, scopolamine, atropine, methyl atropine, tropine, tropic acid, nicotine, dimethyl phenylpiperazinium, arecoline, oxotremorine and pilocarpine. The effects of structural variations, asymmetric centers and steric interactions on the 13C shielding are considered. The observed chemical shifts do not appear to correlate simply with potencies in the cholinergic nervous system.
Mesomere Kationen: III—13C‐Fourier‐Transform‐NMR‐Spektren von Harnstoffen, Thioharnstoffen und Guanidinen
Authors: Kalinowski Hans‐Otto , Kessler Horst
Published: May 2005

Die 13C‐chemischen Verschiebungen von methylsubstituierten Harnstoffen, Thioharnstoffen und verwandten Verbindungen werden diskutiert. Es wurde eine Korrelation von 13CO und 13CS‐chemischen Verschiebungen gefunden. Die mittlere Anregungsenergie im paramagnetischen Verschiebungsanteil wird für die Änderung der Verschiebungen bei Übergang von Carbonyl‐ zu entsprechenden Thiocarbonyl‐Verbindungen als wesentlich angesehen. Einfache HMO‐Berechnungen der Ladungsdichte können die Trends der 13C‐chemischen Verschiebungen nicht wiedergeben.
Kernresonanzspektroskopische Untersuchungen an C6H2F2(SCH3)2‐Isomeren: Das [AMX3]2Spinsystem
Authors: Hägele Gerhard , Richter Jens , Peach Michael
Published: May 2005

Aus CH3SNa und 1,2,4,5‐ bzw. 1,2,3,4‐Tetrafluorobenzol wurden 1,2‐Difluor‐4,5‐dimethylthiobenzol bzw. 1,4‐Difluor‐2,3‐dimethylthiobenzol dargestellt. Die Struktur der beiden C6H2F2(SCH3)2‐Isomeren wurde durch kernresonanz‐spektroskopische Methoden bestimmt. Der subspektrale breakdown des [AMX3]2‐Spinsystems wird für den Sonderfall verschwindender long‐range‐Kopplungen abgeleitet.
Conformational analysis of β‐methoxyalkylmercuric chlorides by NMR spectroscopy and extended hückel theory
Authors: Ibusuki T. , Saito Y.
Published: May 2005

The energy difference (ΔE) between the two types of rotamers of β‐methoxyethylmercuric chloride has been satisfactorily determined by only assuming the ratio of vicinal trans and gauche HH coupling constants. The validity of the result was confirmed by the large temperature dependence of the vicinal HgH couplings in various solvents. Moreover, it has become possible to determine small values of ΔE in nonpolar solvents. Two ΔE values of β‐methoxypropylmercuric chloride in various solvents were determined on the basis of the substituent electronegativity effect on the HH couplings and their validity was supported by the large temperature dependence of the vicinal HgH couplings. With regard to erythro‐ and threo‐(α‐methyl‐β‐methoxy)propylmercuric chlorides, both the HH and HgH couplings were used to estimate the values of ΔE among the rotamers. Throughout the mercury compounds, it was ascertained that the more polar the solvent, the greater the preference for the conformation with the trans disposed HgCl and OCH3 groups. Excellent agreement between the observed facts and the calculations by extended Hückel theory were shown with regard to the relative magnitude of the rotamer polarity and the conformational energy difference of these mercury compounds.
Chemical shift non‐equivalence of the isopropyl methyl groups of two 10‐isopropoxyergoline‐8β‐methanol derivatives
Authors: Vigevani Aristide
Published: May 2005

The chemical shift non‐equivalence values (about 1 ppm) of the isopropyl methyl groups in the 1H and 13C NMR spectra of the compounds having structure 1 is interpreted as due to the existence of a highly preferred conformation.
Konformationsanalyse und Diastereomerenzuordnung an 1,3‐Aza‐ und 1,3‐Oxaphospholanen mittels paramagnetischer Verschiebung
Authors: Zschunke A. , Hauser A. , Oehme H. , Tauchnitz J.
Published: May 2005

An Dreiding‐Modellen der verschiedenen Konformere von 1,3‐Aza‐ und 1,3‐Oxaphospholanen werden die GeometriefaktorenG[G= (cos2θ – 1)r−3] einzelner Protonen bezüglich eines Koordinationszentrums [Eu(dpm)3] bestimmt. Das Koordinationszentrum wird entweder an dem Sauerstoff der Carbonylgruppe oder an dem Stickstoff oder Sauerstoff im Heteroring gebunden angenommen. Die graphische Darstellung der Geometriefaktoren gegen die paramagnetischen Verschiebungen der betreffenden Protonen ergibt nur für die bevorzugten Konformere bei Zugrundelegung der richtigen Koordinationszentren Geraden. Als Maßzahl für die paramagnetische Verschiebung eines Protons wird die Steigung der Geraden gewählt, die sich beim graphischen Auftragen der chemischen Verschiebung gegen den Gehalt an Eu(dpm)3(in Mol‐%) ergibt. Durch Variation der relativen Konfiguration am C‐Atom 5 an den Modellen und Berechnung der Geometriefaktoren ist es möglich, die unterschiedlichen Diastereomere zuzuordnen, die sich bezüglich der Substituentenstellung am Phosphor und am C‐Atom 5 unterscheiden.
Correlations between molecular parameters and the spin–spin coupling constants of vicinal protons: Criticism of the karplus equations
Authors: Vorontsova L. G. , Bochkov A. F.
Published: May 2005

Conformationally rigid systems such as xylopyranose 1,2,4‐ortho esters (1a) and (1b) and 10‐methoxy‐6‐aza‐isoadamantane (2), for which the identity of conformations both in the crystalline state and in solution can reasonably be assumed, provide good models for the study of experimental correlations between the spin–spin coupling constants (J) of the vicinal protons and the dihedral bond angles (DBA) determined from an X‐ray study in the HCCH bond system. The Karplus equations and their modifications (with and without corrections for the electronegativity of adjacent groups) were found to be unable to provide satisfactory correlations between these parameters. Optimum coefficients for the equations connecting the J and DBA values with corrections for electronegativity were calculated by the least squares method. The same procedure was used to obtain an equation connecting the J with DBA values using the sum of the chemical shifts as a measure of the electronic factors affecting the J ∝ DBA dependence. The accuracy of the equation thus obtained lies within ±18% as opposed to ±48% for the original Karplus equations. A similar correlation was obtained for the angles between the intercrossing lines formed by the directions of the vicinal CH bonds (ILA). When combined with the sum of chemical shifts, ILA provides a better correlation with the coupling constants J than the conventional parameter DBA.
Carbon‐13 NMR spectra of some polychlorinated telomerisation products
Authors: Velichko F. K. , Dostovalova V. I. , Kuzmina N. A. , Fedin E. I. , Freidlina R. Kh.
Published: May 2005

The study of 28 specially selected compounds containing chlorine shows that 13C NMR signals of the CCl3, CCl3CH2 and CH2Cl groups are registered in the ranges of 93 to 105, 49 to 71 and 38 to 59 ppm (from TMS), respectively and are readily identified in 13C NMR spectra of polychloro compounds. The weak electron withdrawing ability of the CCl3CHCl and CH2Cl groups, as well as the extremely strong influence of CCl3 and CH2Cl groups on the methylene group between them in 1,1,1,3‐tetrachloropropane, is noted.
‘Anomalous’ 2J(SnH) coupling in mono– and dichloromethyltin compounds
Authors: Mitchell T. N.
Published: May 2005

The linear relationship between the coupling constants 1J(Sn13C) and 2J(SnH), observed for a number of organotin compounds, does not hold for coupling in the SnCHnCl3−n group of mono‐ and dichloromethyltin compounds. A complete determination of all NMR parameters of the compounds Me3Sn‐CHnCl3−n (n = 0 to 3) shows no further anomalies, indicating that steric factors must be responsible for the unusually low values of 2J(SnH) in the SnCHnCl3−n group. Molecular weight measurements support this theory, showing that the chlorine‐containing compounds are associated.
Restricted rotation in amides. VII—methods of resonance assignment in tertiary amides—an evaluation
Authors: Lewin Anita H. , Frucht Melvin
Published: May 2005

Examination and evaluation of various methods for resonance assignments in amides reveals that only three of these are reliable: (a) the nuclear Overhauser effect, which leads to unequivocal results in tertiary amides; (b) the aromatic solvent induced shift, which is rapid and accurate for tertiary amides without polar substituents; (c) the lanthanide‐induced shift, which although easy, can be applied only to tertiary amides with substituents that do not complex lanthanides.
Concerning the fluorine NMR spectra of steroidal phosphorofluoridates
Authors: Jennings W. Brian , Tolley Malcolm S. , Cooper G. H. , Chittenden Rosemary A.
Published: May 2005

Additional spectral evidence suggests that the previously reported signal doubling in the 19F NMR spectra of certain steroidal phosphorofluoridates is better interpreted in terms of diastereoisomerism than by restricted rotation around the PO bond.
13C NMR spectra of benzofuroxan and related compounds
Authors: Anet F. A. L. , Yavari Issa
Published: May 2005

The 13C n.m.r. spectrum of benzofuroxan at −15°C is assigned on the basis of selective decoupling experiments and by comparison with the 13C chemical shifts of model compounds. The 13C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the 13C spectrum of benzofuroxan in CDCl3, a barrier of 14·0 ± 0·2 kcal mol−1 is obtained for the degenerate tautomerism in this compound.
Nuclear magnetic resonance spectroscopy of Schiff bases: II—imines extracted from aqueous solution
Authors: Pesek Joseph J. , Frost Jack H.
Published: May 2005

Nuclear magnetic resonance spectroscopy is used to study netural imines formed from various aldehydes and primary amines in aqueous solution. The imines are then extracted into CDCl3 and their formation constants in the aqueous phase are calculated as a function of pD. The results are in agreement with previous studies. Decoupling experiments are used to prove that additional splitting of the proton spectrum is due to long range coupling rather than syn‐anti isomerism. The possibility of utilizing the formation of Schiff bases in aqueous solution for synthetic purposes is discussed and the 13C magnetic resonance spectrum of the imine, isolated from the reaction of 2‐thiophenecarbaldehyde and n‐butylamine, is reported.
Sterisch behinderte Rotation in monosubstituierten Ansa‐Verbindungen
Authors: Brink Maud
Published: May 2005

Die Rotationsbarriere um die Pivot‐Bindungen in

equation image

mit n = 8 oder 10 und R = CH2C6H5, CH2COOH, CH2COOCH3 oder CH(CH3)2 wurde studiert; ΔG≠ Werte wurden > 24 Kcal/Mol. gefunden. Die Lösungsmittel‐, Temperature‐ und Konzentrationsabhängigkeit der doppelten, magnetisch nichtäquivalenten Methylenprotonen bzw. Methylgruppen wurde untersucht.
A 1H NMR study of hydrogen bonding and complexation processes of trimethylacetic acid in acetone
Authors: Balevichius V. , Kimtys L.
Published: May 2005

The carboxyl proton chemical shifts of trimethylacetic acid, which was dissolved in acetone and in binary mixtures of acetone and cyclohexane, have been measured as a function of concentration at temperatures of 0, +15, +30, +45 and +60 °C. The results obtained for the system studied, using the equilibrium constant method for interpretation of experimental data, indicate that the molecular association through hydrogen bonds occurs as a monomer‐cyclic dimer‐1:1 complex equilibrium process in the low concentration range (up to 0·08 mol fraction). The equilibrium constants of complexation and dimerization, the chemical shifts of the acid in the complex, and the thermodynamic parameters of complexation and dimerization have been calculated.
Etude stereochimique par RMN du 13C des α‐halogenocyclohexanones
Authors: Jantzen R. , Tordeux M. , de Villardi G. , Chachaty C.
Published: May 2005

L'étude en RMN 13C des halogéno‐2 t‐butyl‐4 cyclohexanones cis et trans permet de mesurer l'influence de la nature et de la stéréochimie des halogènes sur les déplacements chimiques des différents carbones de la molécule. Les incréments sont comparés à ceux obtenus en série cyclohexanique. Par comparaison entre les valeurs des déplacements chimiques expérimentaux et calculés (à l'aide du jeu d'incréments trouvés précédemment) on montre sur des molécules mono‐ et dihalogénées de stéréochimie et de conformation connues, que ces incréments sont à la fois additifs et fonction linéaire de la valeur de la position de l'équilibre conformationnel.
A 1H NMR study of tautomerism in some 1‐arylamino‐3‐aryliminopropenes
Authors: Richards C. P. , Webb G. A.
Published: May 2005

1H n.m.r. spectra at ambient temperatures reveal that an equilibrium exists between the ‘all‐trans’ and ‘all‐cis’ isomers of some of the 1‐arylamino‐3‐aryliminopropenes. The ‘all‐cis’ isomer predominates in nonpolar solvents, whereas the ‘all‐trans’ isomer is favoured in hydrogen bonding solvents. From a consideration of the magnitudes of the 3J coupling constants, it is reported that the ‘cis‐trans’ isomer is the most stable form of the 4‐nitrophenyl derivative in dimethyl sulphoxide.
13C n.m.r. chemical shifts of carbodiimides
Authors: Anet Frank A. L. , Yavari Issa
Published: May 2005

The 13C n.m.r. chemical shifts of the sp‐hybridized carbons in dialkylcarbodiimides have values of δc ≃ 140. These shifts are compared with those of similarly hybridized carbons occuring in other classes of compounds.
Conformational analysis: XIV—A 1H n.m.r. conformational study of methyl substituted 2‐oxo‐1,3,2‐dioxathians to confirm the predominance of chair forms in the trimethylene sulphite series
Authors: Nikander Hannu , Mukkala Veli‐Matti , Nurmi Timo , Pihlaja Kalevi
Published: May 2005

Seven isomeric 4,5,6‐trimethyl‐2‐oxo‐1,3,2‐dioxathians, cis‐4‐trans‐6‐dimethyl‐r‐2‐oxo‐1,3,2‐dioxathian and two isomeric 4,5,5,6‐tetramethyl‐2‐oxo‐1,3,2‐dioxathians were prepared and their 1H n.m.r. spectra analysed. The values of the vicinal coupling constants reported earlier for the cis‐4‐trans‐6 compound were shown to be erroneous. In all cases the values of the vicinal coupling constants (and those of the chemical shifts) are indicative of a single chair conformation or a chair‐chair equilibrium, in contrast to earlier reports on the significant contribution of twist forms but in agreement with an electron diffraction study. The chair form is ≳ 31 kJ mol−1 thermochemically more stable than the twist form.
13C n.m.r. spectroscopy: Comparison of the spectra of some dimeric Catharanthus alkaloids and their derivatives
Authors: Dorman Douglas E. , Paschal Jonathan W.
Published: May 2005

The 13C n.m.r. spectra of some dimeric Catharanthus alkaloids are reported and assigned. Methods devised to aid in the assignment of resonances in complex molecules are described. The 13C n.m.r. spectra of several derivatives of vinblastine are discussed.
Carbon‐13 n.m.r. studies of some saturated 1,2‐oxazepine derivatives
Authors: Rice Kenner C. , Wasylishen Roderick E.
Published: May 2005

The influence of incorporating an group, an oxygen atom and the fragment in a saturated 7‐membered ring system on carbon‐13 n.m.r. chemical shifts is examined, and also, the influence of the dioxolane ring moiety on the 13C chemical shifts in these ring systems. Substituent effects are generally additive except in cases where the ring is heavily substituted with methyl groups. A large upfield steric shift (γ effect) of 7–8 ppm is observed in two of the derivatives. An example of long range nonequivalence is also observed. Assignments of the 13C n.m.r. spectra have been made by comparison with model compounds, and from proton coupled 13C n.m.r. spectra. The synthesis of several new compounds is described.
Effets stériques des groupes alkyle sur le déplacement chimique des hydrogènes d'un méthyle: Correlation avec les termes Es de Taft
Authors: Roussel C. , Gallo R. , Chanon M. , Metzger J. , Bernassau J. M.
Published: May 2005

L'effet des groupements alkyle de la série Me, Et, i‐Pr, t‐Bu sur le déplacement des hydrogènes d'un groupe méthyle, situé en ortho, est relié linéairement aux paramètres d'effets stériques (Es) de Taft dans des structures du type 1.

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Une équation Δδ = δR – δMe = λ′Es rend compte des résultats expérimentaux. λ′ dépend du solvant et du modèle utilisé. Les calculs des déplacements chimiques suivant les approches d'ApSimon et de Buckingham confirment la prépondérance des effets stériques sur l'effet de substituant observé.
RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique
Authors: Grenier‐Loustalot M. F. , Iratçabal P. , Forchioni A. , Metras F.
Published: May 2005

Nous avons enregistré les spectres RMN du 13C d'une série de quatorze chlorocyclohexanones afin d'examiner les variations du déplacement chimique du 13C en fonction de la position de l'orientation et du nombre de substituants chlore. On détermine par comparaison entre les valeurs des déplacements chimiques expérimentaux et calculés de molécules chlorée, des incréments Δδ13C et les conditions de leur additivité. La comparaison des déplacements chimiques observés et calculés dans le cas de molécules mono et dichlorées en interconversion, montre que les effets du chlore sont additifs.
2,3,5,6‐Tetramethylmorpholine: II—1H n.m.r. structural studies of the isomers of 2,3,5,6‐tetramethylmorpholine
Authors: Hernestam Sven , Nilsson Bertil
Published: May 2005

The structures of the six isomers of 2,3,5,6‐tetramethyl‐morpholine have been determined by means of proton nuclear magnetic resonance studies at 100 MHz. The spectra have been analysed in terms of spin–spin coupling constants and population distributions of the possible conformers at low temperatures. Also included in this paper are results from n.m.r. studies on the six 4‐benzyl‐2,3,5,6‐tetramethylmorpholine derivatives, which give information about the stereochemistry of the methyl groups α to the amine group.
Natural abundance nitrogen‐15 n.m.r. spectroscopy. Spin–lattice relaxation in organic compounds
Authors: Levy George C. , Holloway Clive E. , Rosanske Richard C. , Hewitt James M. , Bradley Craig H.
Published: May 2005

The small negative magnetogyric ratio (γ) of the 15N nucleus decreases the efficiency of 15N1H dipole‐dipole relaxation to about 25% of that for an analogous 13C nucleus. This may lead to greater competition from other relaxation mechanisms in 15N n.m.r. and consequent partial or total quenching of the negative nuclear Overhauser effect (NOE). In unfavorable circumstances nulling of the 15N resonance can occur. Previous 15N relaxation studies have examined isotopically enriched, low molecular weight compounds. The present study examines several small to intermediate size organic compounds containing nitrogen at natural isotopic abundance. In contrast to some of the earlier studies, 15N1H dipolar relaxation was found to be dominant for protonated nitrogen atoms, even for two tertiary nitrogens (the tertiary amine nitrogen in 1,2,3,4,6,7,12,12b‐octahydroindolo[2,3‐a] quinolizine and the oxime nitrogen in 3‐methyl‐2‐pentanone ketoxime). The magnitude of the NOE and the moderate value of T1 indicate effective dipolar relaxation from neighboring but not directly bonded protons in these cases. Nitro groups were found, as expected, to have predominant contributions from non‐dipolar mechanisms, and in one case (2‐methyl‐2‐nitro‐1, 3‐propanediol) signal nulling (NOE of η = −1) was observed. The effect of paramagnetic impurities was demonstrated for ethanolamine, which contains a basic nitrogen. In this case T1DD(15N1H) = 4·3 s; added Ni(acac)2 at 1 × 10−4 Molar reduced the 15N T1 to 0·065 s and consequently the NOE to η = 0.
13C n.m.r. spectroscopy of diethyl alkyl‐ and benzyl‐phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds
Authors: Ernst Ludger
Published: May 2005

13C chemical shifts and31P13C spin–spin coupling constants are reported for 10 alkyl‐, 20 benzyl‐ and 3 (naphthylmethyl)‐phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects onJ(PC) are studied and discussed.nJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates andnJ(PP) (n = 5, 6, 7) were obtained from the13C satellites in the31P n.m.r. spectra of the isomeric diphosphonates, C6H4[CH2P(O)(OEt)2]2. Comparison of those13C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH3C6H4CH2P(O)(OEt)2, yielded the relative signs ofnJ(PC) (n = 2–6).
Nuclear magnetic resonance studies: VII—13C and 15N n.m.r. of diazo compounds
Authors: Albright Thomas A. , Freeman Walter J.
Published: May 2005

The 13C and 15N n.m.r. results for a series of diazo compounds are reported. It is found that the diazo carbon is shielded by an extraordinary amount compared with normal sp2 hybridized carbons. The 15N chemical shifts reveal that the terminal nitrogen is deshielded relative to the central one. This is contrary to that expected from charge effects but support is found for this phenomenon in other systems. One‐bond 13C14N coupling in diazomethane is also reported for the first time. INDO MO calculations of the charges and finite perturbation calculations of 13C14N and CH couplings are compared with the experimental results.
N.m.r. spectra of prostaglandin metabolites and precursors and of related pyrazoline adducts
Authors: Rackham David M. , Cowdrey Sarah E. , Gutteridge Norman J. A. , Osborne David J.
Published: May 2005

The 13C n.m.r. spectra of the major human urinary metabolite of prostaglandin PGE2 and PGE1 are discussed together with some unsaturated precursors. Δ‐2‐Pyrazolines, formed by addition of diazomethane to the 11‐oxo dienediones in this series, were identified by 13C and 1H n.m.r. and by other physical methods.
Proton shielding increment values for the benzenesulfonyl group in saturated and unsaturated sulfones
Authors: Bongini Alessandro , Savoia Diego
Published: May 2005

Some alkyl and alkenyl phenyl sulfones have been examined and the additive proton shielding increments calculated for the benzenesulfonyl group.
13C n.m.r. investigation on the first and second nitrogen protonation in the diazanaphthalenes
Authors: van de Weijer Peter , van den Ham Dirk M. W. , van der Meer Douwe
Published: May 2005

The 13C chemical shifts of the diazanaphthalenes have been recorded as a function of the pH value, providing classical titration curves. From these curves the pK1 and pK2 values have been determined taking into account the activity coefficients. The changes in 13C chemical shift under the influence of nitrogen protonation (Δδ) can be described by two protonation parameter sets.
Kernresonanzspektroskopische Untersuchungen ancis‐(CH3)2Pt[P(OCH3)3]2
Authors: Hägele Gerhard , Lorberth Jörg
Published: May 2005

100 MHz1H NMR Spektren voncis‐ (CH3)2Pt[P(OCH3)3]2werden als Superposition von [AR3X9]2‐und [AR3X9]2M ‐Systemen analysiert. Diecis‐Struktur wird abgeleitet von den KopplungskonstantenJ(PP) undJ(PtP).
Carbon‐13 n.m.r. analysis of selected strychnos alkaloids
Authors: Leung J. , Jones Alan J.
Published: May 2005

The carbon‐13 chemical shifts of strychnine and ten closely related analogues have been assigned and confirmed in several cases using selective proton decoupling techniques. Where additivity relationships are used the importance of having data on an array of structural analogues is emphasized. Quaternization at N‐19 exerts long range polarization effects throughout the molecular framework. The effects of N‐oxide formation on the carbon‐13 shifts of 5 to 9‐membered ring heterocycles and strychnine are discussed as aids to structural assignment. A Zwitterionic structure for strychnic acid is deduced.
Carbon‐13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives
Authors: Cheng A. K. , Stothers J. B.
Published: May 2005

The 13C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.02,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.02,406,8]nonane are also reported.
Determination of the conformation of 1,4‐diheterocyclanes. I—The1H n.m.r. spectrum and ring conformation of 3‐methyl‐2‐oxo‐1,4‐dioxepane
Authors: Äyräs Pertti , Partanen Annikki
Published: May 2005

The1H n.m.r. spectrum of 3‐methyl‐2‐oxo‐1,4‐dioxepane was recorded at 300 and 60 MHz. The ring conformation was considered in terms of the spectral parameters and shown to be a twisted boat where the lactone grouping is approximately planar.
Analyse du spectre de RMN protonique du cyclobutanedithiol‐1,1
Authors: Fournier Claude , Lemarié Bernard , Braillon Bernard , Paquer Daniel , Vazeux Michel
Published: May 2005

Cette note traite de la synthèse et de l'analyse du spectre de RMN protonique à 90 MHz du cyclobutanedithiol‐1,1. Les déplacements chimiques et les constantes de couplage sont rapportés et la discussion de ces dernières a permis de préciser la conformation de cette molécule.
Étude en RMN du 13C de Dérivés de la Pipéridone‐4 Stériquement Encombrés et des Oximes Correspondantes
Authors: Geneste P. , Kamenka J. M. , Brevard C.
Published: May 2005

Les différences de déplacements chimiques régiospécifiques introduites par la fonction oxime permettent, à l'aide de paramètres (Δδ et Δδ), d'estimer les modifications conformationnelles directement à partir des spectres de 13 C. En particulier, les conformations croisées résultant de l'oximation de pipéridones stériquement encombrées sont détectées sans ambiguité.
Carbon‐13 n.m.r. study of 31P13C spin–spin coupling constants in dichloro‐ and monochloro‐vinyl phosphate derivatives
Authors: Szalontai Gábor
Published: May 2005

Carbon‐13 chemical shifts and J(PC) coupling constants of 29 vinyl phosphate derivatives are presented. In the series of compounds (R1O)2P(O)OC1(R)C2X2 (where 3 in R indicates the first carbon of the R2 substituent) large differences were found between the 3J(P, O, C‐1, C‐3) and 3J(P, O, C‐1, C‐2) coupling constants of the chlorinated (XCI) and the unsubstituted (XH) derivatives. A possible explanation of this phenomenon is given on the basis of Jameson's s bond character theory. Strong stereospecificity of 3J(P, O, C‐1, C‐3) coupling constants was observed in the series of compounds (R1O)2 P(O)OC1(R)C2HR3. Coupling constants varied between 3.2–4.9 Hz in the E isomers, while peaks could not be resolved in the Z isomers. The 3J(P, O, C‐1, C‐2) coupling constants were regularly 20–30% greater in the Z than in the E isomers.
Temperature dependence of the chemical shifts of commonly employed proton n.m.r. reference compounds
Authors: Cross Bradford P. , Schleich Thomas
Published: May 2005

The temperature dependence of the chemical shifts of ten commonly employed 1H n.m.r. reference compounds of interest to both organic and biological workers was determined using the temperature independent standard ethane at low density. The water soluble standards sodium 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate and sodium 3‐trimethylsilylpropionate‐d6 exhibited very small chemical shift changes over the range of 20–65 °C. Outside of this temperature interval the chemical shift is distinctly nonlinear, but still is sufficiently small to be neglected for many n.m.r. studies. In contrast, the temperature dependence of seven neat organic liquid reference standards was observed to be linear over a significant temperature range with slopes varying between 0.0009 and 0.0023 ppm °C−1. Only tetramethylammonium chloride (in 2H2O) exhibited a small but pronounced nonlinear temperature dependence over the full range investigated.
Carbon‐13 n.m.r. investigation on the nitrogen methylation of the mono‐ and diazanaphthalenes
Authors: van de Weijer Peter , Mohan Chandra , van den Ham Dirk M. W.
Published: May 2005

The 13C n.m.r. spectra of the N‐methylated mono‐ and diazanaphthalenes have been recorded and analysed. It has been shown that N‐methylation as well as N‐protonation in cinnoline occur predominantly at the β‐nitrogen atom. N‐methylation and N‐protonation show a similar effect on the 13C chemical shifts.
The interpretation of carbon nuclear magnetic resonance shifts. 3.. The variation of the local diamagnetic shielding term in 13C N.m.r., as determined by calculation and by X‐ray photoelectron spectroscopy
Authors: Mason Joan
Published: May 2005

Experimental values of ‘chemical shifts’

The term ‘chemical shift’ is used in the general sense, as by physicists and physical chemists (cf. chemical shifts in Mössbauer spectroscopy, or as here, X‐ray photoelectron spectroscopy). The chemical shift δ, as measured in n.m.r. spectroscopy, is then the algebraic sum of the ‘chemical shift’ in the local diamagnetic shielding term, ΔσAp in the paramagnetic term, ΔσAp and, the contribution from the rest of the molecule, in the local term approximation.

in the local diamagnetic term σAd for carbon in a wide range of groupings have been obtained from X‐ray photoelectron spectroscopic measurements of chemical shifts in the C‐Is binding energy. Eb. This conversion is possible because σAd and Eb both depend directly on the electrostatic potential within the valence shell; thus Eb increases, and σAd calculated by an extended Flygare method (in which CNDO‐calculated atomic charges are used to interpolate Hartree‐Fock values of σd for the free atom A and ± ions) show that the extended Flygare method values are reliable, differential relaxation effects in the photo‐emission process being small. Agreement is also good with published ab initio values of σAd. The range of variation in σAd for carbon is 7–8 ppm from C2H2 to CF4, or 10 ppm if one includes negative ions such as CN−. Some problems of the local term approximation are discussed, and comparison made with the atom‐plus‐ligand ‘local’ term approximation.
Résonance Magnétique Nucléaire. V.—Etude de Chlorures Vinyliques par RMN 1H. Incréments spécifiques des radicaux alkyle
Authors: Abudarham J. P. , Meyet J. , Smadja W. , Levisalles J.
Published: May 2005

Isolés et identifiés, vingt‐cinq chlorures vinyliques ont été caractérisés par résonance magnétique du proton (RMN 1H), par chromatographie en phase vapeur (CPV) et, pour certains, par voie chimique. De nouveaux incréments spécifiques du groupe alkyle géminé au proton vinylique sont proposés. L'effet du chlore sur les hydrogènes vinyliques allyliques et homoallyliques est décrit, ainsi que l'effet de solvant du benzène.
1H n.m.r. spectra of N‐phenylmaleimide in isotropic and nematic phases
Authors: Khetrapal C. L. , Diehl P. , Kunwar A. C.
Published: May 2005

1H n.m.r. spectra of N‐phenylmaleimide have been investigated in isotropic as well as nematic phases; the chemical shifts, the direct dipolar and the indirect spin–spin coupling constants have been determined. The direct dipolar coupling constants are consistent with rapidly interconverting energetically equivalent twisted conformations of C2 symmetry. Under the assumption that only two such conformers are predominantly present, the angle between the phenyl and the maleimide planes is determined as 52.9±0.9°.
Etudes d'Alkylidènehydrazono‐2 Méthyl‐3 Dihydro‐2,3 Benzothiazoles par RMN 1H en Présence d'Eu(fod)3
Authors: Richer Jean‐Claude , Beljean Martine , Pays Michel
Published: May 2005

L'étude des spectres RMN 1H, en présence d'Eu(fod)3, d'une série d'alkylidènehydrazono‐2 méthyl‐3 dihydro‐2,3 benzothiazoles démontre que le site de coordination du complexe de lanthanide sur les deux azotes de ces azines varie en fonction de facteurs qui peuvent étre stériques ou polaires.

Cette étude permet également de déterminer les configurations Z ou E des azines étudiées ainsi que les proportions relatives des isomères en solution dans différents solvants.
Carbon‐13 nuclear magnetic resonance of the azomethine group. II—(II.II) conjugation and twist angles
Authors: Solladié‐Cavallo A. , Solladié G.
Published: May 2005

Torsional angles in some mono‐substituted conjugated benzenes were determined from the chemical shift of the para carbons. Similar results were obtained from ketones and imines, and the torsional angles increase, as expected, with steric hindrance. It is possible to assign a syn or anti stereochemistry for the imines from the value of the torsional angle.
Carbon‐13 n.m.r. of the 8‐phosphabicyclo[3.2.1]octane system
Authors: Rudi A. , Kashman Y.
Published: May 2005

13C Chemical shifts and 13C31P nuclear spin coupling constants have been determined for 26 8‐phosphabicyclo[3.2.1]octane derivatives, namely phosphines, phosphine oxides, phosphine sulphides and one phosphonium salt. The influence of the phosphorus configuration on δ and 2J(PC) values was examined and other factors influencing the 2J(PC) coupling constant are discussed.
Calculation of some boron nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A.
Published: May 2005

Boron screening constants and their anisotropies have been calculated for 23 trivalent boron compounds. The calculations have been performed within a framework in which gauge‐dependent atomic orbitals are used in the molecular orbital description. Reasonable agreement with experimental chemical shifts is found when CNDO/S parameters are used; INDO calculations are less satisfactory. No correlation is found between the observed chemical shifts and those estimated from the Average Excitation Energy approach. Similarly, no correlation is found with total boron charge densities although agreement is reported with π charge density. In trimethylboron the lowest energy σ→π* transition dominates the in‐plane contributions to the local paramagnetic term while various σ→π* transitions dominate the out‐of‐plane contributions.
Sur l'Utilisation de la Stéréospécificité des Couplages Magnétiques à Longue Distance dans la Détermination des Conformations d'Aziridines Bicycliques
Authors: Rouillard Michel , Férrero Louis , Geribaldi Serge , Azzaro Marcel
Published: May 2005

L'étude des couplages magnétiques à longue distance relevés dans les spectres RMN du proton à 60 MHz d'aziridines du type aza‐7 bicyclo[4.1.0]heptane, permet de préciser la conformation de ces composés et de démontrer sans ambiguïté l'existence de structures bloquées pour certains isomères.
NMR studies in the heterocyclic series. XVIII—Carbon‐13 NMR study of azolium salts. Attempted correlation of chemical shifts with calculated charge densities
Authors: Fayet Jean‐Pierre , Vertut Marie‐Claire , Fruchier Alain , Tjiou El Mostafa , Elguero José
Published: May 2005

The carbon‐13 chemical shifts and the 1J(CH) coupling constants for 18 azolium salts (di‐N‐methyl‐pyrazolium, ‐indazolium, ‐benzimidazolium and ‐benzotriazolium iodides) have been determined and assigned. The chemical shifts are discussed as a function of substituent effects, positive charge introduction and total electronic density (calculated by the CNDO/2 method). The general problem of correlations between chemical shifts and total charge densities in azoles is discussed. A statistical approach shows that these correlations are of poor quality.
Remarks on the analysis of dynamic 1H NMR spectra of A3B2 ⇌ C3D2 spin systems. Internal rotation in N,N‐diethylbenzamide
Authors: Gryff‐Keller Adam , Szczeciński Przemyslaw
Published: May 2005

A method of analysis of dynamic NMR spectra for A3B2 ⇌ C3D2 spin systems is proposed. This method is based upon the assumption that the shape of the A–C part of the spectrum is the same as for the AB2 ⇌ CD2 spin system and the shape of the B–D part is the same as for the A3B ⇌ C3D system. By means of this simplification the iterative total line shape analysis of dynamic NMR spectra by the use of the least‐squares method becomes feasible. The method proposed is applied to the determination of the thermodynamic parameters of activation for internal rotation in N,N‐diethylbenzamide in CD3CN (ΔG = 62.6 kJ mol−1 ΔH≠ = 62 kJ mol−1, ΔS≠ = −1 J/mol−1 K−1). The determination of natural line widths is discussed in detail and a method of estimation of the effect of systematic errors on the results is proposed.