bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interpretation of substituent‐induced chemical shifts in 13C NMR spectra of 2‐substituted norbornadienes. Influence of homoconjugation
Authors: Krawczyk Hanna , Szatylowicz Halina , Gryff‐Keller Adam 
Published: May 2005

AbstractComplete signal assignments and an interpretation of the 13C NMR spectra of bicyclo[2.2.1]hepta‐2,5‐diene and of 12 of its 2‐substituted derivatives are presented. The substituent effects observed at C‐1, C‐2 and C‐3 are very similar to those reported for 2‐substituted propenes and monosubstituted benzenes. Transmission of those effects on C‐5 and C‐6 may be at least partially attributed to the homoconjugative interaction between the double bonds in the systems investigated. The relative importance of the field and the resonance effects at particular positions have been evaluated by the dual substituent parameter analysis of the chemical shift data. Relationships between substituent‐induced chemical shifts and electron densities, calculated by the PM3 method, have been found.
29Si and 13C NMR spectra of tert‐butyldimethylsilyl derivatives of amino acids
Authors: Kubec Roman , Velíšek Jan , Kvíčalová Magdalena , Čermák Jan , Schraml Jan 
Published: May 2005

Abstract29Si and 13C NMR chemical shifts are reported for tert‐butyldimethylsilyl (TBDMS) derivatives of ten common amino acids. The 29Si chemical shifts of TBDMS derivatives of various functionalities encountered fall into distinct spectral regions. The 29Si chemical shifts correlate linearly (r = 0.999) with the 29Si shifts reported earlier for the trimethylsilyl (TMS) derivatives of the same amino acids, the 29Si chemical shift values in the TBDMS derivatives being larger than those in the TMS derivatives (in SiN groups this downfiled shift varies between 3.8 and 5.8 ppm and in SiO groups between 1.4 and 1.7 ppm).
Determination of signs of coupling constants [1J(77Se29Si), 2J(77Se13C), 3J(77Se1H)] in 2,5‐dihydro‐1,2,5‐selenasilaborole derivatives
Authors: Wrackmeyer Bernd , Köster Roland , Seidel Günter 
Published: May 2005

AbstractThe signs of coupling constants [1J(77Se29Si) > 0, 2J(77Se13CSiMe) > 0,3J(77Se1HSiMe) > 0] were determined for pentaorgano‐substituted 2,5‐dihydro‐1,2,5‐selenasilaboroles [R3 = Me, la; R3 = C(Me)CH2, 1b], and also for derivatives in which the surroundings of the selenium atom were changed by forming a pyridine‐borane adduct (2), by formation of an SeAlCl3 adduct (3) and by π‐complexation with the transition metal fragments [Fe(CO)3] (4) and [Ru(CO)3] (5). The sign determination was achieved by using various types of 2D heteronuclear shift correlations (HETCOR) with 13C, 29Si or 1H detection (HMQC). Some of these experiments had to be modified by z‐filtering or by a Ψ‐BIRD pulse sequence. The change in the magnitude of 1J(13C13C) (la, 58.9 Hz; 4, 33.8 Hz) as a result of π‐complexation follows the trend known for diene complexes.
Investigation of substituted dihydronaphthalenes using 1H and 13C NMR spectroscopy
Authors: Alam Todd M. , Liu Ming‐Eng , Garcia Daryl K. , Hernandez Valerie M. , Malone Richard R. , Chamblee Brian B. , Deck Lorraine M. , Royer Robert E. 
Published: May 2005

Abstract1H and 13C NMR studies were carried out on the substituted dihydronaphthalene compounds 1,2‐dihydro‐8‐isopropyl‐6,7‐dimethoxy‐2‐methylnaphthalene, 3‐bromo‐1, 2‐dihydro‐8‐isopropyl‐6, 7‐dimethoxy‐2‐methylnaphthalene, 3, 4‐dihydro‐5‐isopropyl‐6, 7‐dimethoxy‐3‐methyl‐1(2H)‐naphthalenone, 1, 2‐dihydro‐6, 7‐dimethoxy‐2, 8‐dimethylnaphthalene, 3‐bromo‐1, 2‐dihydro‐6, 7‐dimethoxy‐2, 8‐dimethylnaphthalene and 3, 4‐dihydro‐6, 7‐dimethoxy‐3, 5‐dimethyl‐1(2H)‐naphthalenone. Complete assignments of the proton and carbon spectra were made using one‐ and two‐dimensional NMR techniques including APT, COSY, NOESY and 1H‐13C HETCOR spectroscopy.
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

AbstractCondensation 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

AbstractThe 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

AbstractBroad 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

AbstractSolid‐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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractPulsed 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

AbstractImportant 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

AbstractThe 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

Abstract4J(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

AbstractBy 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.
Substituent effects in proton NMR of monosubstituted acetophenones: I
Authors: Caplin G. A. 
Published: May 2005

AbstractChemical 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

AbstractThe 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

AbstractCarbon‐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

AbstractDie 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

AbstractAus 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractConformationally 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

AbstractThe 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

AbstractThe 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

AbstractExamination 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.