bluuebunny/crossref_metadata_2025 huggingface dataset:
Substituent‐induced chemical shifts of aromatic carbon centres in a series of non‐acetylated and peracetylated Para‐substituted aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides
Authors: Roy René , Tropper François D. , Williams Antony J.
Published: May 2005

The additive behaviour generally observed for the substituent‐induced chemical shifts (SCS) for disubstituted benzenes was examined for a series of aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides having a wide range of para substituents with varying possible electronic contributions. The SCS values associated with non‐acetylated and peracetylated glucoside rings in para‐substituted aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides were calculated. The additive nature of SCS analysis for para‐substituted systems was shown to hold for the meta and para positions but the very small change in chemical shifts for the ortho positions precluded attempts at analysis of these data. The observation of a good correlation for the ipso carbons for the acetylated compounds compared with a poor correlation for the same site in the non‐acetylated compounds is not well understood.
Carbon‐13 NMR spectral assignments of some bicyclo[4.3.0]nonanone and bicyclo[4.4.0]decalone systems
Authors: Rao H. Surya Prakash , Reddy K. Subba
Published: May 2005

Carbon‐13 NMR signal assignments of some bicyclo[4.3.0]nonan‐4‐ones (hydrindanones) and bicyclo[4.4.0]decal‐4‐ones are reported.
Sur les complexes formés par le trifluorure de bore avec les sulfoxydes, aminoxydes, phosphinoxydes et arsinoxyde: Aspects généraux des spectres de RMN (1H,11B,19F et31P)
Authors: Bravo R. , Durand M. , Laurent J.‐P.
Published: May 2005

Les spectres de résonance magnétique nucléaire (1H,11B,19F et31P) des complexes RnMO·BF3formés par le trifluorure de bore et des sulfoxydes, aminoxydes, phosphinoxydes et arsinoxydes ont été obtenus. Les paramètres (déplacements et couplages) caractérisant ces spectres sont comparés à ceux de composés similaires renfermant également une liaison de coordination O·B.
Mise en evidence de la chiralité de l'édifice spirophosphoranique
Authors: Houalla D. , Sanchez M. , Wolf R.
Published: May 2005

La chiralité de l'édifice spirophosphoranique dans le mélange racémique 2a, 2ā, est décelée, en RMN, à l'aide d'inducteur de déplacement chimique optiquement actif.
Dynamic NMR: A single operational parameter approach for evaluation of lifetime in an uncoupled, equally populated AB system
Authors: Dimitrov Valentin S.
Published: May 2005

Two simple formulae involving only one variable are presented for the simple and rapid estimation of the mean lifetime (τ) of exchange in uncoupled, paripartite AB systems. These formulae are shown to provide τ values comparable to those obtained from total line‐shape analysis.
NMR spectrum of 1‐chloronaphthalene orientated in the nematic phase
Authors: Diehl P. , Vogt J.
Published: May 2005

The NMR spectrum of 1‐chloronaphthalene has been studied in the nematic phase of N‐(p′‐ethoxybenzylidene)‐p‐n‐butylaniline. Ratios of interproton distances have been derived.
Determination of the erythro and threo configuration of the two diastereoisomeric 2‐amino‐3‐mercaptobutyric acids by NMR spectroscopy of derived thiazolidines
Authors: Toppet S. , Claes P. , Hoogmartens J.
Published: May 2005

A study of the 1H and 13C NMR spectra of the N‐formyl‐2,2,5‐trimethyl‐4‐carboxythiazolidines and the N‐formyl‐4‐carboxy‐5‐methylthiazolidines derived from the two diastereoisomeric 2‐amino‐3‐mercapto‐DL‐butyric acids, permits unambiguous assignment of the erythro and threo configuration of these amino acids. The spectra of the N‐formylthiazolidines, recorded in DMSO‐d6 solution, reveal the presence of two conformational isomers with a low rate of interconversion. The geometry around the carbon–nitrogen bond and correlated conformations of the 5‐membered ring in both forms are discussed.
Temperature dependent NMR spectra of oxazepines, thiazepines, oxazocines and thiazocines
Authors: Puar Mohindar S. , Yale Harry L. , Cohen Allen I.
Published: May 2005

The temperature dependence of several 7‐membered 5‐substituted‐5,11‐dihydrodibenz[b,e] [1,4]oxazepines (Z = O) and thiazepines (Z = S), as well as of 8‐membered 12‐substituted ‐6,11‐dihydro‐12H‐dibenz[b,f] [1,4]oxazocines (Z = O) and thiazocines (Z = S), has been studied by NMR spectroscopy. The average ΔF* (kcal/mol) values at coalescence temperatures are 14·0 (M = CHO), 18·2 (M = COCH3) for oxazepines, 17·3 (M = CHO), >21 (COCH3) for thiazepines, and 13·0 for oxazocines and 13·3 for thiazocines, respectively. These data show that replacement of oxygen by a sulfur atom raises the barrier height of ring inversion, but that this effect is greater with the 7‐membered than with 8‐membered heterocycles. Thus the 8‐membered rings have a greater degree of flexibility than do the 7‐membered ones. With the oxazepines and the thiazepines, it was also possible to measure the thermodynamics (ΔF*, ΔH* and ΔS*) of the hindered rotation around the NCO bond by studying the temperature dependence of the formyl and acetyl proton resonances. The results suggest that the processes of conformational inversion and hindered rotation in the same molecule are independent of each other. The rate of hindered rotation is slower than the rate of conformational inversion. The conformational preferences of the compounds are also discussed.
NMR spectra of 1,3‐butadienes: VII—the conformation of 2,4‐dimethyl‐2,4‐pentadiene
Authors: Cunliffe A. V. , Harris R. K.
Published: May 2005

Proton magnetic resonance spectra of 2,4‐dimethyl‐2,4‐pentadiene have been examined for a number of solution conditions and (for a CF2Cl2 solution) over a range of temperatures. Coupling constants for the ethylenic protons were obtained from double resonance (methyl decoupled) spectra. Further double resonance experiments established the sign of 4Jc. It is found that 4Jc = −1·20 Hz and [4Jt] = 0·18 Hz. It is concluded that the compound exists in a single nonplanar conformation with an average dihedral angle (from the s‐cis form) ϕ = 50° ± 15°. Some long range coupling constants involving the methyl group were found to be appreciable in spite of the lack of planarity of the diene chain.
On the NMR spectrum of 1,3‐oxathiane‐3‐oxide: A contrast between the conformational preference of the sulphinyl oxygen in 1,3‐oxathiane‐3‐oxide and in 1,3‐dithiane‐1‐oxides
Authors: Bergesen Knut , Cook Michael J. , Tonge Alan P.
Published: May 2005

The 100 MHz spectrum of 1,3‐oxathiane‐3‐oxide is reported. Parameters obtained from first order analyses are interpreted in terms of an absence of a conformational preference of the SO bond at 38°C, but an axial preference at low temperatures. The behaviour contrasts with that found previously in the 1,3‐dithiane‐1‐oxide series.
Hindered rotation about the amido NC bond and the tautomeric equilibrium in N,N‐dimethylacetoacetamide
Authors: Hobson R. F. , Reeves L. W. , Shaddick R. C.
Published: May 2005

The molecule N,N‐dimethylacetoacetamide, which is subject to a keto–enol equilibrium process in solution, also exhibits hindered rotation about the amido NC bond. The hindered rotation rates have been studied by lineshape fit methods of the nuclear magnetic resonance spectra. In spite of some overlap of the keto and enol N‐methyl proton signals, the simultaneous measurement of the two distinct energy barriers in the two forms is possible as well as a determination of the keto–enol equilibrium. The differences in free energy of activation between keto and enol forms for the rotation barrier can be related to the conjugation energy of the NC π system with the enolic hydrogen bonded ring. Appeal to the model compound acetylacetone reveals a consistent set of energies for the keto and enol forms in the ground and transition states for internal rotation. The opportunity has been taken to reexamine and compare the keto–enol system ethylacetoacetate. Long range, solvent, concentration and temperature sensitive scalar couplings 4J(HH) between the enolic –OH and the adjacent methyl group in acetoacetic ester have not hitherto been reported.
Hétérocycles contenant du phosphore. XXIII—Etude par RMP de dérivés de l'oxazaphospholane‐1,3,2: III—Interprétation des résultats. Tentative d'analyse conformationnelle
Authors: Devillers Jean , Cornus Martine , Navech Jacques
Published: May 2005

Moyennant certaines hypothèses, il est possible de déterminer la conformation au niveau du fragment C4C5 des différents dérivés de l'oxazaphospholane‐1,3,2 dont les paramètres de RMP ont été préalablement calculés.
Nuclear magnetic resonance spectra of pyrido‐ and azapyridocyanines
Authors: Leubner Ingo H.
Published: May 2005

The nuclear magnetic resonace spectra of six pyridocyanines, four azapyridocyanines, one monoquaternized 2,4′‐dipyridylamine and two dipyridylamines were measured and fully analyzed. The spectra of the 2,2′‐pyrido‐ and azapyridocyanines support previously published results that these dyes exist in the all‐trans form and not in the mono‐cis form, as stated by others. Strong evidence was obtained that N,N′‐ethylene‐2,2′‐pyridocyanine is twisted. The spectra of dyes with p‐connected pyridine rings indicate that these nuclei may rotate around the bond between the meso group and the p‐position. Relative chemical shifts in the spectra of the homologous pyrido‐ and azapyridocyanines can be explained by electronic effects rather than by magnetic anisotropy of the aza group or changes in ring currents.
Utilisation de la RMN a champs forts dans la série du norbornène: triméthylsilyl‐endo‐3 bicyclo (2.2.1) heptène‐5
Authors: Gassend R. , Limouzin Y. , Maire J. C.
Published: May 2005

La RMN à 250 et à 300 MHz combinée à des expériences de double irradiation de type classique ou INDOR a été utilisée pour établir sans ambiguité la structure endo d'un triméthylsilyl‐3 norbornène‐5. Les déplacements chimiques et les constantes de couplage ont été très exactement déterminés, des couplages à longue distance n'obéissant pas à la ‘règle du W’ ont été mis en évidence.
Ring strain effects: VI—benzocyclobutadienoquinone radical anion
Authors: Rieke Reuben D. , Westmoreland David G. , Rieke Loretta I.
Published: May 2005

Electron paramagnetic resonance studies were carried out on the radical anion of 4‐deuterobenzocyclobutadienoquinone. The hyperfine coupling constants which had been assigned previously were found to be in error. The effects of the strained 4‐membered ring on the spin density distribution are discussed.
Solvent effects on the proton magnetic resonance spectra of thio‐ and dithio‐oxamides
Authors: Lepoivre J. A. , Desseyn H. O. , Alderweireldt F. C.
Published: May 2005

The chemical shifts of the N‐methyl signals for a number of thio‐oxamide and oxamide derivatives are unambiguously determined in the solvents chloroform, carbon tetrachloride, benzene, chlorobenzene, o‐dichlorobenzene and nitrobenzene. The ASIS effect is discussed. The temperature dependence of the absolute shift and of the relative shift differences of both methyl groups of the N,N‐dimethyl derivatives are studied.
NMR studies of sulphur heterocycles. II—substituent effects in the thieno[2,3‐b] [1]benzothiophene and thieno[3,2‐b] [1]benzothiophene systems
Authors: Ewing D. F. , Gregory D. N. , Scrowston R. M.
Published: May 2005

Substituent chemical shifts for the title systems have been determined at infinite dilution in CDCl3 from a study of 40 derivatives. An excellent correlation is found between the ortho effect of substituents in the thiophene ring and the corresponding effects in thiophene itself, indicating negligible perturbation by the fused rings. Long range effects of 2‐ and 3‐substituents on the 5‐ and 6‐protons are electronic in origin, but cannot be interpreted in terms of simple resonance theory. These long range effects correlate linearly with σp°. An O, S‐cis conformation for the formyl group in 2‐formyl‐thieno[2,3‐6][1]benzothiophene is adduced on the basis of chemical shifts.
Analysis of fine splittings in the fourier transform 1H magnetic resonance spectra of some 15N labeled borazine derivatives
Authors: Turbini Laura J. , Porter Richard F.
Published: May 2005

Proton NMR spectra are reported for 15N enriched borazine and a series of 15N enriched derivatives: N‐methyl‐borazine, N,N′‐dimethylborazine and a new photochemical product, 1‐methyl‐2‐aminoborazine. Chemical shifts for the ring (15NH) protons have been measured. Using a Fourier transform spectrometer, fine structure in the 15NH doublet is resolved. Ortho and meta ring proton and three‐bond 15N to H coupling constants have been determined. Substituent effects on chemical shifts and coupling constants for borazine derivatives are compared with those for analogous benzene derivatives.
A theoretical study of nuclear spin coupling constants and hyperfine coupling constants of se‐heterocyclics
Authors: Galasso V. , Bigotto A.
Published: May 2005

MO calculations based on the finite perturbation theory in the INDO approximation have been carried out on selenophene, eighteen of its monosubstituted derivatives and benzo (b)selenophene. The calculated nuclear spin coupling constants satisfactorily reproduce signs, magnitudes, internal orders and some trends of the experimental values. Comparison of different ZDO calculations provides information on the relative importance of σ and π pathways for the various coupling constants in selenophene and benzo(b)selenophene. Unrestricted Hartree‐Fock calculations at the INDO level have been performed on the radical anions of dibenzoselenophene and 2,1,3‐benzoselenadiazole, the phenoselenazine radical cation, the phenoselenazine neutral radical and the phenoselenazine nitroxide. The isotropic hyperfine coupling constants have been found to be generally in satisfactory agreement with experiment.
Systèmes aromatiques à 10 électrons π dérivés de l'aza‐3a pentalène. IX—etude par RMN de l'équilibre azide/tetrazole dans le cas du tetrazolo [5,1‐b] benzothiazole
Authors: Faure R. , Galy J. P. , Giusti G. , Vincent E. J. , Elguero J.
Published: May 2005

Nous avons observé l'équilibre azide‐tétrazole dans le cas du tétrazolo [5,1‐b] benzothiazole par résonance magnétique nucléaire du proton à 250 MHz, en solution dans le deutériochloroforme. L'analyse des spectres a permis la détermination des déplacements chimiques et des constantes de couplage des deux formes tautomères.
Long range 31P1H couplings in phosphorylated iminothiazolines and iminooxazolines
Authors: Tseng C. K. , Mihailovski A.
Published: May 2005

Long range 31P1H coupling constants of 21 phosphorylated iminothiazolines and two phosphorylated iminooxazolines have been studied. The size of the 31P1H coupling in the HCNCNP framework is larger than that in the HCSCNP framework which is in turn larger than the HCOCNP framework. The value of the 31P1H coupling through the HCNCNP framework decreases in the order of P > PS > PO, whereas a reverse trend is observed for the HCSCNP framework. A planar zig‐zag configuration has been proposed for the long range 31P1H couplings.
Study of the intrinsic and conformational solvent effects on the chemical shift of the aldehydic proton in furfural and thiophenealdehyde
Authors: Bertrán José Fernández , Rodríguez Mario
Published: May 2005

The chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents. The correlation of the chemical shifts of thiophenealdehyde and benzaldehyde is excellent (r = 0·996) while it is lower for furfural–benzaldehyde (r = 0·956). The long range coupling constant Jα5 of furiurai has been measured in twelve solvents and the rotameric mole fractions determined. The chemical shifts of individual rotamers are calculated and shown to correlate with benzaldehyde, (r = 0·992; 0·993). Only one rotamer is predominant for thiophenaldehyde in all solvents. The intrinsic solvent effects of the three aldehydes are similar.
Benzo‐ and indoloquinolizine derivatives. VI—configuration and conformation of 4b,5,6,7,8,8a,10,11,16,16b‐decahydrodibenz[f,h]indolo[2,3‐a]quinolizine diastereoisomers. A 270 MHz 1H NMR study
Authors: van Binst G. , Tourwé D.
Published: May 2005

The synthesis of a D/E cis isomer of the title compound is described. In an attempt to obtain the other D/E cis isomer, epimerisation reactions were studied. The configuration and conformation of the isomers are determined on the basis of their 1H NMR spectra. The shift of the 16b proton on N‐9 protonation indicates the quinolizidine conformation. At 270 MHz, the ABCD system of the C‐10 and C‐11 methylenes can be analysed. The 2J(C‐10H2), together with the multiplicity of H‐8a, allows an unequivocal assignment of a cis‐anti‐cis structure to the only D/E cis isomer obtained.
Intrinsic carbon‐13 NMR solvent shifts in hydrocarbons. Relevance of long range substituent parameters
Authors: Wilson A. R. N. , van de Ven L. J. M. , de Haan J. W.
Published: May 2005

Carbon‐13 NMR chemical shifts have been measured in a number of binary mixtures of normal alkanes. Intrinsic solvent shifts are deduced from the shifts and the relevance of some small substituent effects in alkanes is discussed. A comparison is made between solvent effects and thermally induced chemical shift differences in alkanes.
Influence of methyl substituents on the chemical shift of the ring protons in mono‐, di‐ and trimethylcyclohexanes a 300 MHz study of the 1H NMR spectrum of cis‐1,3‐dimethylcyclohexane
Authors: Danneels Dirk , Anteunis M.
Published: May 2005

From a 300 MHz spectral study of mono‐to trisubstituted cyclohexanes, allowing a re‐examination of some of their 1H NMR spectral parameters, it is shown that it is possible to predict with reasonable accuracy the shifts (in CCl4) of the ring protons. A substantial feature in this is the validity of the (questioned) additivity of multiple effects. It is also shown that with respect to shift alterations, equatorial ring protons behave anomalously, which cannot be explained by any existing theoretical model.
Theoretical and empirical calculations of the carbon chemical shift in terms of the electronic distribution in molecules
Authors: Martin G. J. , Martin M. L. , Odiot S.
Published: May 2005

The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ13C are pointed out. The variations of the excitation energy ΔE, the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ13C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ13C and the electronic charge, electronegativity, Hammett‐Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.
composés cycliques à six chaǐnons
Authors: Cazaux Louis , Navech Jacques
Published: May 2005

Diverses méthodes de calcul sont proposées pour calculer l'angle de torsion de la liaison CC dans les composés cycliques à six chaǐnons. Elles fournissent un ordre de grandeur correct de cet angle par comparaison avec les mesures aux rayons X. La limite de cette détermination est montrée.
Long range substituent effects relfected in the 13C NMR spectra of allyl alcohols and their derivatives
Authors: Wenkert Ernest , Gašić Miroslav J. , Hagaman Edward W. , Kwart L. D.
Published: May 2005

Acylation of allyl alcohols induces strong carbon shifts, shielding γ and deshielding δ effects. These shifts are a consequence of through‐bond polarization of the olefinic carbons. Allyl ethers show similar, but milder perturbations. The olefinic carbon shifts reveal a strong concentration dependence. This effect, in greatly reduced form, is also observed in non‐oxygenated alkenes. Hydrogen bonding by alcohols enhances the chemical shift difference in olefinic carbon pairs by increased polarization.
Carbon‐13 nuclear magnetic resonance chemical shifts and 13C‐199Hg coupling constants for symmetrical dialkylmercurials
Authors: Casanova J. , Rogers H. R. , Servis K. L.
Published: May 2005

The carbon‐13 chemical shifts and coupling constants (J[13C199Hg]) have been determined for a series of eleven symmetrically substituted organomercurials. Empirical substituent parameters can be calculated which correlate observed and predicted chemical shifts for dialkylmercurials.
A NMR investigation of proline and its derivatives. II—Conformational implications of the 1H NMR spectrum of L‐proline at different pH
Authors: Pogliani L. , Ellenberger M. , Valat J.
Published: May 2005

The 250 MHz 1H NMR spectrum of L‐proline is comprehensively analysed by computer simulation for different pH values. A fast endo–exo interconversion has already been proposed from chemical shift and coupling constant data. A critical comparison of the vicinal coupling constants leads to the conclusion that in basic solution the equilibrium is shifted towards a more endo conformation. The position of the carboxylic plane in the ring space is given by the relative intramolecular chemical shift of the geminal protons and by the typical patterns of the Hα multiplet. These results are applied to the analysis of the spectra of ProNH2 and AcProNH2.
Reaction de redistribution entre le tripropylbore et ses produits d'oxydation: Etude par résonance du Noyau 11B
Authors: Cros G. , Costes J. , Laurent J‐P.
Published: May 2005

L'étude par résonance magnétique nucléaire (11B) des systèmes formés par le tripropylbore et l'anhydride borique met en évidence l'intervention de réactions de redistribution entre le tripropylbore et ses produits d'oxydation, c'est‐à‐dire de redistributions mettant en jeu des groupements monofonctionnels (C3H7) et difonctionnels (O) sur des atomes de bore tricoordonnés.
Proton NMR spectrum of indene oriented in the nematic phase
Authors: Diehl P. , Vogt J.
Published: May 2005

The proton NMR spectrum of the 8‐spin system of indene has been studied in the nematic phase of N‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline. Orientation parameters and ratios of interproton distances have been derived and are compared with the results of an electron diffraction study.
Hochauflösungs‐13C‐NMR‐Spektroskopie. II—Die Spektren von (2‐Dimethylamino‐1‐propenyl)triazinen
Authors: Braun S. , Frey G. , Bachmann M.
Published: May 2005

Die unentkoppelten 13C‐NMR‐Spektren der bei der Reaktion von Methyltriazinen mit 1‐Äthoxy‐1‐(dimethylamino)‐äthylen entstandenen Produkte wurden mit Hilfe der Puls‐Fourier‐Transform‐Technik aufgenommen und analysiert. Der Vergleich der beobachteten 13C‐chemischen Verschiebungen und 13CH‐Kopplungskonstanten mit denen der Ausgangstriazine und des 2‐Dimethylamino‐2‐penten‐4‐ons bestätigt die (2‐Dimethylamino‐1‐propenyl)triazin‐Struktur. Die Daten werden im Hinblick auf sterische Effekte sowie die Konfiguration und Konformation der Seitenkette diskutiert.
Unresolvable long range spin–spin coupling as a source of systematic error in proton NMR total bandshape analysis
Authors: Drakenberg Torbjörn , Carter Robert E.
Published: May 2005

Unresolvable long range spin‐spin coupling which is not explicitly taken into account in total NMR bandshape analysis is demonstrated to be a potentially important source of systematic error, leading to ΔH≠ and δS≠ values incorrect by c. 1 kcal/mol and 2 to 4 cal/(mol K), respectively.
Etude par RMN du carbone des systèmes CN: imines, phénylhydrazones, semicarbazones, amidines, iminoéthers
Authors: Naulet N. , Filleux M. L. , Martin G. J. , Pornet J.
Published: May 2005

Ce travail présente une étude par RMN de carbone‐13 de composés comportant une double liaison CN simple et conjuguée (iminoéthers, imines aliphatiques, imines éthyléniques, amidines, oximes, phénylhydrazones, semicarbazones). L'influence de la stéréoisomérie Z/E, des substituants et le rǒle de l'effet stérique sur le déplacement chimique sont discutés.
1H NMR spectra of E and Z pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone and related compounds
Authors: Bell C. F. , Mortimore G. R.
Published: May 2005

Proton magnetic resonance spectra at 100 MHz are reported for the E‐ and Z‐isomers of pyridine‐2‐carbaldehyd 2′‐ pyridylhydrazone in carbon tetrachloride, d6‐dimethylsulphoxide and d6‐benzene solutions, and for various monomethylated derivatives in d6‐dimethylsulphoxide. The spectral parameters obtained by analysis with the help of LAOCOON 3 are discussed in terms of solvent effects and the chemical shift changes consequent upon isomerisation are evaluated. Some conclusions are reached concerning the preferred conformations of the E‐ and Z‐isomers of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone.
Parameter errors in LAOCOON 3 calculations
Authors: Ewing D. F.
Published: May 2005

Some model calculations with LAOCOON 3 have been used to show that the mean error in the calculated coupling constants is linearly related to the root mean square error in the transition frequencies. On the basis of this linearity it is shown that the ‘probable’ error parameter of LAOCOON 3 should be increased by a factor of 2·5 to give more realistic errors.
13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols
Authors: Paasivirta Jaakko , Laihia Katri
Published: May 2005

Carbon chemical shifts and direct 13C1H coupling constants of 2‐endo‐methyl‐5‐norbornen‐2‐exo‐ol, 2‐exo‐methyl‐5‐norbornen‐2‐endo‐ol, 2‐endo‐methylnorbornan‐2‐exo‐ol and 2‐exo‐methylnorbornan‐2‐endo‐ol have been measured from single samples using a dual probe pulse Fourier transform method.
35Cl/37Cl isotope effects on 13C chemical shifts. Assignment of carbon‐13 NMR lines of polychlorinated hydrocarbons
Authors: Buchner W. , Scheutzow D.
Published: May 2005

An isotope effect of about 0·1 Hz at 25 MHz (0·004 ppm) on the 13C chemical shifts due to directly bonded chlorine has been observed at −50°C for hexachloropropene, hexachlorobutadiene and tetrachlorobutenyne. This effect yields an unambiguous assignment of 13C NMR lines to specific carbon atoms in these polychlorinated hydrocarbons.
Vicinal C,H spin coupling in substituted alkenes. Stereochemical significance and structural effects
Authors: Vogeli U. , von Philipsborn W.
Published: May 2005

Vicinal C,H spin coupling (3JC,H) in substituted alkenes has been investigated systematically. Emphasis is laid on the stereochemical significance (Jtrans/Jcis) and on the various structural factors which influence 3JC,H, such as π‐bond order, torsional angle ϕ, bond angle θ, electronegativity of substituents and steric effects. A new type of γ‐effect is observed in 3JtransC,H which appears to have the same origin as the γ‐shift effect. By comparison of 3J and 3JH,H, it was found that the relation 3JC,H ≈︁ 0·6 3JH,H holds for both trans and cis coupling constants. Finally, it is concluded that 3JC,H constitutes a valuable criterion to distinguish E‐ and Z‐isomers, particularly in trisubstituted alkenes. Applications to natural products are presented.
15N nuclear magnetic resonance spectroscopy. Natural abundance 15N NMR of monosubstituted indoles
Authors: Rosenberg E. , Williamson Kenneth L. , Roberts John D.
Published: May 2005

15N chemical shifts of twenty‐four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2‐, 3‐ and 5‐ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl3. 13C NMR data for previously unreported compounds are also reported.
13C nuclear magnetic resonance studies on some substituted isoxazoles
Authors: Gainer James , Howarth Graham A. , Hoyle William , Roberts Stanley M.
Published: May 2005

13C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4‐substituted 3,5‐dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C‐5 methyl.
13C, 15N coupling constants in substituted 1,2,4‐triazines‐4‐15N
Authors: Braun S.
Published: May 2005

The 13C,15N coupling constants in three 1,2,4‐triazine‐4‐15N derivatives and in a substituted pyrimidine‐1‐15N have been determined and are compared with those in pyridine and quinoline. Of special interest are the data of the 5‐(2‐dimethylamino‐1‐propenyl)‐3,6‐dimethyl‐1,2,4‐triazine‐4‐15N, since one observes a characteristic alternation of the absolute value of J(13C,15N) along the sidechain and a hitherto unobserved very large 13C,15N coupling constant through four bonds of 3·9 Hz, the origin of which is attributed to the influence of the lone pair orbital on the 15N at position 4.
Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques
Authors: Gobert F. , Combrisson S. , Platzer N. , Ricard M.
Published: May 2005

Les conséquences en RMN 1H et 13C de l'effet péri induit par un phényle ont été étudiées en série anthracénique. On a pu montrer que les contributions stériques s'élevaient à 25% de l'effet total. Le modèle de Johnson et Bovey est susceptible de décrire correctement la zone de blindage du phényle seul. En RMN 13C, les blindages et déblindages inattendus observés chez les dérivés très encombrés sont probablement liés à des distorsions du squelette anthracénique.
13C Fourier transform n.m.r.: XIII—reassignment of the 13C spectrum of ergosterol
Authors: Cushley Robert J. , Filipenko J. Douglas
Published: May 2005

The complete labeling pattern of ergosterol isolated from Saccharomyces cerevisiae grown with [1‐13C] acetate is detailed and the results of this study have led to a reassignment of carbons 5, 8, 12, 16, 22 and 23 in the 13C n.m.r. spectrum of ergosterol.
Proton n.m.r. spin‐tickling studies of 13C‐labeled compounds. The correlation of J(C,H) and J(H,H)
Authors: Marshall James L. , Seiwell Ruth
Published: May 2005

A tabulation has been compiled for twenty 13CH coupling constants of various carboxylic acids and includes 2J(C,H), 3J(C,H) and 4J(C,H) values of olefins (both cis and trans); 3J(C,H), 4J(C,H) and 5J(C,H) values of aromatics; 3J(C,H) and 4J(C,H) values of acetylenes; and 2J(C,H) and 3J(C,H) values of rigid aliphatics. This tabulation has been completed in the present study by the spin‐tickling proton n.m.r. study of 13C‐carboxyl‐endo‐1,2,3,4,7,7‐hexachloronorbornene‐5‐carboxylic acid, which has established that the 2J(C,H) value is negative and the 3J(C,H) values (both cis and trans) are positive in this system. A plot of these twenty J(C,H) values vs the corresponding J(H,H) values of geometrically equivalent model systems (where there is a proton in place of a carboxyl group) gives a correlation coefficient of 0·975 (with a slope of 0·62), indicating that carbon–proton and proton–proton couplings operate by similar mechanisms throughout this broad series of structural types.
Conformational investigations on cyclic dipeptides containing a proline residue by means of 13C n.m.r. spectroscopy
Authors: Siemion Ignacy Z.
Published: May 2005

The amounts of boat (A) and planar (B) forms for the equilibrium state in D2O and CD3OD/d6‐DMSO (1:1) were calculated for seven proline‐containing cyclic dipeptides from their 13C n.m.r. spectra. For c‐Pro‐Val the thermodynamic functions for the conversion between the boat and planar forms have been obtained from measurements of equilibrium constants at different temperatures.
15N13C coupling constants in 15N labelled azaadamantane
Authors: Berger Stefan , Kaletsch Hans
Published: May 2005

The 15N13C coupling constants in 15N labelled azaadamantane have been measured and interpreted in terms of their conformational dependence as compared with 15N‐quinuclidine.
Theoretical calculations of nuclear spin coupling of phosphorus to carbon and hydrogen by the finite perturbation method
Authors: Albright Thomas A.
Published: May 2005

Finite perturbation calculations using CNDO/2 wave functions are presented for the determination of 31P13C and 31P1H couplings. The calculations were carried out on 46 molecules and a comparison with experimental values is given. The groups of compounds considered were phosphonium cations, phosphine oxides, alkylidenephosphoranes, phosphine sulfides, phosphoranes and phosphines. With the exception of phosphines, the finite perturbation approach reproduces the experimental couplings with fair accuracy. It is found that there is a good correlation with the calculated 1J(P, C) and the phosphorus 3s‐carbon 2s bond orders for tetra‐ and pentavalent phosphorus compounds. This lends support to the growing body of evidence for the direct relationship of the magnitude of 1J(P, C) and percent s character in the hybrid orbital on the carbon comprising the PC bond. The finite perturbation technique was also used to explore the effects of geometrical changes on PC and PH couplings. Finally, the effect of deleting d orbitals on phosphorus is discussed briefly.
Sélénophènes substitués. Additivité de l'influence des substituants sur les couplages J(HH) et J(SeH)
Authors: Simonnin M. P. , Pouet M. J. , Cense J. M. , Paulmier C.
Published: May 2005

Les différents couplages J(HH) et J(SeH) mesurés dans divers sélénophènes 2‐ et 3‐substitués, dont les signes ont été déterminés par double résonance, ont été reliés aux constantes de réactivité de Swain et Lupton par des équations linéaires J = i + fF + rR. L'importance relative de la contribution des effets inductifs et mésomères est discutée. Dans les sélénophènes 2,4‐disubstitués, l'effet des deux substituants sur les couplages J(HH) et J(SeH) est additif. Cette loi d'additivité rend compte du changement de signe de 3J(SeH) observé dans le dinitro 2,4‐sélénophène. Les conformations préférentielles des formyl 2‐ et 3‐sélénophènes, déduites des couplages à longue distance, sont respectivement SeO cis et SeO trans.
The use of the selective population inversion technique in the assignment of carbon‐13 n.m.r. resonances in 3,6‐epoxy‐pentacyclo[6.2.1.02,7.04,10.05,9]undecane
Authors: Dekker T. G. , Pachler K. G. R. , Wessels P. L.
Published: May 2005

Different applications of the selective population inversion technique in an n.m.r. study of 3,6‐epoxypentacyclo‐[6.2.1.02,7.04,10.05,9] undecane have been demonstrated. The intensity gain accompanying heteronuclear 13C—{1H} experiments allowed the detection of fine structure due to long range CH couplings otherwise hidden in normal proton coupled 13C spectra. Definite assignments of two very similar, directly bonded, CH couplings within a methylene group have been made.
13C spin relaxation studies of the basic pancreatic trypsin inhibitor
Authors: Wüthrich Kurt , Baumann Rudolf
Published: May 2005

The longitudinal 13C spin relaxation times T1 and the 13C{1H} nuclear Overhauser enhancement were measured in a concentrated aqueous solution of the basic pancreatic trypsin inhibitor. The correlation time for overall rotational motions of the basic pancreatic trypsin inhibitor molecules was found to be τR ≈ 2 × 10−8 s. In connection with previous 1H n.m.r. studies of intramolecular motions of the aromatics, we were particularly interested in the correlation times τG for intramolecular segmental motions of the aromatic rings. The present experiments revealed no manifestation of intramolecular motions of the aromatics, indicating that τG ≫ 2 × 10−8 s for the aromatic ring carbon atoms. On the other hand, rapid segmental motions were evidenced for the peripheral carbon atoms of aliphatic amino acid sidechains. Comparison of the 1H and 13C n.m.r. data on the basic pancreatic trypsin inhibitor indicates that the time scale of high resolution 1H n.m.r. at high fields may in many instances be more appropriate for studies of the molecular dynamics in globular proteins than the time scale of spin relaxation measurements.
A 13C n.m.r. study of the B6 vitamins and of their aldimine derivatives
Authors: Harruff Richard C. , Jenkins W. Terry
Published: May 2005

The vitamins, pyridoxine, pyridoxal, pyridoxamine, pyridoxal‐5′‐phosphate and pyridoxamine‐5′‐phosphate, have been studied in aqueous solution over a pH range of 2–12 by 13C nuclear magnetic resonance spectroscopy. Resonance assignments are made primarily by the spin–spin coupling constants of carbons with protons and with phosphorus. The proton–carbon coupling constants show a marked conformational dependence in the hemiacetal form of pyridoxal. Furthermore, the H‐6C‐5 coupling constant in the vitamins is much smaller than the corresponding constant in pyridine. This may be due either to an effect of the C‐5 substituent in vitamins or to a different electronic configuration of the zwitterionic hydroxypyridine ring. The addition of manganese to a solution of pyridoxal phosphate causes line broadenings consistent with the interaction of the metal ion with this vitamin at the formyl and phenolic oxygens. The chemical shifts of the aromatic carbons of pyridoxine have been calculated, as a function of pH, by summing shielding parameters which were estimated empirically from pyridine derivatives. The calculated shifts agree well with the experimental data for C‐3, C‐5 and C‐6, less well for C‐2, and poorly for C‐4. The deviation from additivity for C‐4 indicates a preferred orientation for the 4‐hydroxymethyl substituent caused by internal hydrogen bonding between the substituents at C‐3 and C‐4. Evidence is presented for the existence of the free aldehyde form of pyridoxal at alkaline pH. Aldimine complexes of pyridoxal and pyridoxal phosphate with amines and amino acids have also been studied. Characteristic chemical shift changes caused by both pyridinium and aldimine nitrogen deprotonations are seen. Additionally, the chemical shifts of carbons of the pyridine ring are dependent upon the structure of the imine, especially when the aldimine nitrogen is protonated. We conclude that this dependency is due to steric effects in an aldimine complex which is constrained by internal hydrogen bonding. We also discuss the merits of carbons 3 and 4 as possible sites of cofactor labeling for enzymatic studies.
A unified correlation of substituent effects with carbon, proton and fluorine chemical shifts in aromatic and olefinic systems
Authors: Smith William B. , Proulx Thomas W.
Published: May 2005

At the present time no completely satisfactory quantum mechanical calculations exist for carbon, proton or fluorine chemical shifts in various substituted aromatic or olefinic systems. However, the chemical shifts in such systems have been shown to be well correlated by a linear multiple regression analysis with the Swain and Lupton field and resonance para meters ℱ and ℛ, and the semiempirical parameter Q. The utility of Q in testing substituent stereochemistry has been exemplified previously. Here the applications of the complete regression analysis to a wide variety of different systems for the three nuclei are given. The correlation is also shown to apply to selenium in substituted selenophenes. The 13C chemical shifts for a series of ortho substituted toluenes are presented and comparisons made with other ortho disubstituted benzenes.
Carbon‐13 nuclear magnetic resonance spectra: III—2‐heteroadamantanes
Authors: Duddeck Helmut , Wolff Peter
Published: May 2005

The 13C n.m.r. spectra of some 2‐heteroadamantanes and 1‐substituted 2‐heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the 13C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2‐mono‐ and 2,2‐disubstituted adamantanes. The nonadditivity of the substituent effects for 1‐substituted 2‐heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH2 group and of NCH3 carbons upon the 13C chemical shifts of the carbons in the adamantane system are described.
Photolyse d'oxazirannes: VI—Détermination par RMN du proton des configurations et conformations privilégiées d'oxazirannes à jonction spirannique
Authors: Oliveros Esther , Riviere Monique , Lattes Armand
Published: May 2005

Les structures d'imines et d'oxazirannes dérivés de la méthyl‐2 et de la diméthyl‐2,6 cyclohexanone ont été déterminées par RMN 1H. Nous avons pu montrer que pour tous les oxazirannes étudiés, la conformation préférentielle correspond à une position équatoriale de l'azote.
Automatic analysis of n.m.r. spectra; a practical application to the spectra of oriented 2,4‐dichlorobenzaldehyde and 2‐chlorobenzaldehyde
Authors: Diehl P. , Vogt J.
Published: May 2005

The capabilities of a novel computer program for the ‘automatic analysis of n.m.r. spectra’ [J. Magn. Reson. 19, 67 (1975)] are demonstrated in the analysis of the experimental spectra of oriented 2,4‐dichlorobenzaldehyde and 2‐chlorobenzaldehyde. In both cases solutions are found by starting from parameters which do not allow a line assignment. The fitting procedure is described in detail and the conclusion is reached that the program is a typical search program which is able to find, fully automatically, parameters which are unknown in principle. However, for reasons of efficiency, a certain amount of interaction between the computer and the spectroscopist is desirable. The structural results indicate that in both molecules, which are assumed to be planar, the O‐trans‐configuration vastly predominates and that the benzene rings are considerably distorted.
Electronic effects in some 3‐substituted‐2‐cyclohexenones: A study by carbon‐13 n.m.r. spectroscopy
Authors: Bedford G. R. , Taylor P. J.
Published: May 2005

The carbon‐13 n.m.r. spectra of some 3‐substituted‐2‐cyclohexenones show very wide variations in chemical shift at C‐3 that correlate with Pauling electronegativity χ, even wider variations at C‐2 that correlate with the Taft resonance parameter σRº and almost no variation at C‐1. These very different effects are shown to be consistent with the electronic distribution for these and related compounds revealed by other spectroscopic techniques. Reasons for the insensitivity of carbon‐13 n.m.r. to configurational and conformational variation in simple enamino‐ketones are discussed.
Determination of 3J(31P31P) and 13C31P coupling constants in 1,6‐diphosphatriptycene from carbon‐13 n.m.r. lone pairs effects on 13C31P couplings
Authors: Sørensen S. , Jakobsen H. J.
Published: May 2005

The 31P31P and 13C31P coupling constants in 1,6‐diphosphatriptycene have been obtained from analysis of its proton decoupled 13C n.m.r. spectra. More accurate data, however, resulted from simultaneous analysis of the proton decoupled 13C spectra and 31P(13C) satellite spectra. The 13C31P couplings are strongly influenced by the proximity and orientation of the phosphorus lone pair electrons. The first 31P31P coupling in an aromatic diphosphine is reported.
Résonance Magnétique Dynamique du Carbone: IV—Application à l'Étude Conformationnelle des Thiourées
Authors: Filleux‐Blanchard Marie‐Louise
Published: May 2005

Une étude par spectroscopie 13C d'une série de thiourées est réalisée. Des informations sont obtenues sur l'équilibre conformationnel. Une rotation empěchée des groupes tert‐butyle est mise en évidence. Les effets de substituant sont examinés.
Constantes de couplage vicinales à travers deux hétéroatomes: III—Calculs théoriques et mesures expérimentales dans les hydrazides enrichies en 15N
Authors: Elguero José , Johnson Brian L. , Pereillo Jean‐Marie , Pouzard Guy , Rajzmann Michel , Randall Edward W.
Published: May 2005

Divers calculs, dont celui utilisant la méthode des perturbations finies avec des fonctions d'onde INDO, ont été effectués pour calculer la valeur du couplage 3J(1HNN1H) dans les hydrazides en fonction de l'angle dièdre. Les résultats expérimentaux (1H, 13C, 15N) sont examinés à la lumière de ces calculs. Le premier exemple d'un couplage 2J(1HN15N) est décrit.
A caution regarding the use of LAOCOON III for AA′BB′ spin systems
Authors: Manatt Stanley L.
Published: May 2005

It has been found that LAOCOON III can fail to converge for some strongly coupled AA′BB′ spin systems unless trial coupling constants and chemical shifts within a few tenths of a Hz of the real parameters are used to initiate the iteration. This problem seemed linked to those spin systems possessing two or more pairs of energy levels which are nearly degenerate. In the cases where LAOCOON III failed, the program NMRENIT always yielded the correct, converged, iterative solution even with completely arbitrary starting parameters. The latter program also appears to accomplish a given number of iterations with an AA′BB′ system roughly three times as fast as the former program.
Conformational analysis of the dibenzo [a,g]‐quinolizidines by spectroscopic means. II—The use of high resolution 270 MHz proton magnetic resonance
Authors: Tourwé D. , Van Binst G. , Kametani T.
Published: May 2005

The 270 MHz 1H n.m.r. spectra of some model tetrahydroprotoberberines have been analysed and the dependence of the chemical shifts and the geminal and interbenzylic coupling constants on the conformation examined. Their use for conformational analysis was illustrated on two 8‐methyl substituted epimers.
The n.m.r. spectra of porphyrins. 13—A ring current model for the porphyrin and chlorin (7,8‐dihydroporphyrin) rings
Authors: Abraham Raymond J. , Fell Stephen C. M. , Smith Kevin M.
Published: May 2005

The equivalent dipole model of the ring current shift in benzene is shown to be equivalent to that of the well‐known two current loop calculation. A network model of the ring current effect in the porphyrin system is described, using the double–dipole approximation, to give a calculation of the ring current shifts in the porphyrin system; this agrees with the observed shifts of protons both in the ring‐plane and above it. A simple modification of the model enables treatment of ring current shifts in the chlorin ring. These models may be used to provide, very simply, good estimates of the ring current shifts of the porphyrin and chlorin rings at points above and outside the current loops; the agreement is sufficiently good to allow assignments of peripheral substituents to be made, and to provide information on their orientation. The model is consistent with a peripheral ring current loop in both the free‐base porphyrins and their metal complexes. The relationship of these results to calculations in polycyclic aromatics and to protonation shifts in porphyrins is discussed.
Carbon‐13 nuclear magnetic resonance spectra: V—substituent interactions at 4‐substituted adamantanones and bicyclo[2.2.2]octanones
Authors: Duddeck Helmut , Wolff Peter
Published: May 2005

The 13C n.m.r. data of a variety of 4eq‐ and 4ax‐substituted adamantanones and bicyclo[2.2.2]octanones are presented. It is shown that for a number of carbons the chemical shifts cannot be predicted by a given additivity rule. The deviations of the observed chemical shifts from the calculated ones are discussed in terms of different interaction mechanisms operating through the σ bond frameworks or through space.
A new stable spiropyranic aminyloxide (nitroxide)
Authors: Balaban Alexandru T. , Negoita Nicolae , Baican Roman
Published: May 2005

The N‐hydroxy‐spiropyran 1‐hydroxy‐3‐oxoindoline‐2‐spiro‐4′‐[2′,6′‐diphenyl‐4′ H‐pyran], prepared according to Van Allan et al. starting from a 4‐methyl substituted pyrylium salt, can be readily oxidized to the corresponding aminyloxide. This can be obtained in the crystalline state and may be kept as such for years without modification. The e.s.r. spectra were investigated in the solid and in solution.
Intensity gains with a progressive saturation SPI n.m.r. experiment. The degenerate A—{X3} case
Authors: Pachler Klaus G. R. , Wessels Philippus L.
Published: May 2005

An Ft n.m.r. experiment is described which may lead to a substantial increase in the peak height of n.m.r. signals.