bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractAt 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

AbstractThe 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

AbstractLes 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractUne 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

AbstractDivers 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

AbstractIt 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.
Carbon‐13 n.m.r. study of naturally occurring xanthones
Authors: Westerman Philip W. , Gunasekera Sarath P. , Uvais M. , Sultanbawa S. , Kazlauskas Rymantas 
Published: May 2005

AbstractThe 13C n.m.r. spectra of 36 naturally occurring xanthones are reported and all chemical shifts assigned. The shifts in substituted xanthones can be predicted from substituent effects evaluated for simple derivatives. The agreement between calculated and observed shifts decreases as the extent of substitution in the xanthone increases.
The carbon‐13 spectra of steroids on the way to ecdysone
Authors: Smith William B. 
Published: May 2005

AbstractA combination of chemical shift reagent effects, partially relaxed spectra, and carbon T1 measurements have been used to assign the chemical shifts of the carbons in seven different steroids which have served as intermediates in a synthesis of the steroid moulting hormone ecdysone. The assignments of ergosterol have been completed. It has been shown that the T1's are consistent with the molecular structures.
A rotational barrier about the isopropyl to aryl bond in highly substituted sulphines
Authors: Tangerman Albert , Zwanenburg Binne 
Published: May 2005

AbstractThe rotational barriers in sulphines containing the substituents 2,6‐dimethyl‐3‐isopropyl‐4‐methoxyphenyl and 4,6‐dimethyl‐3‐isopropyl‐2‐methoxyphenyl are discussed. Particular attention is given to the occurrence of a barrier to rotation about the isopropyl to aryl bond. In both types of sulphines the isopropyl group is flanked by a methyl and a methoxy group. The isopropyl to aryl barrier could only be detected in the sulphines containing the second type of substituent where the o‐methoxy group experiences a buttressing effect from the CSO moiety.
Étude des Phénomènes de Redistribution dans les Systèmes BR3/BT3 avec T = –OCH3, –SCH3, –N(CH3)2
Authors: Costes Jean‐Pierre , Cros Gérard , Laurent Jean‐Pierre 
Published: May 2005

AbstractL'étude des spectres de résonance nucléaire (1H, 11B) de différents mélanges BR3/BT3/ avec T = OCH3, SCH3 et N(CH3)2 met en évidence l'existence d'équilibres de redistribution entre les espèces BRnT3–n (n = 0, 1, 2, 3). II apparaǐt que, d'une façon générale, les espèces mixtes (n = 1 et 2) sont plus favorisées que ne le laisserait prévoir un modèle de redistribution au hasard. Les facteurs d'ordre stérique et électronique susceptibles d'intervenir dans ces réactions sont envisagés.
On the assignment of 13C resonances in unsymmetrical ortho‐disubstituted benzene rings. 13C N.m.r. spectrum of Piroxicam
Authors: Whipple Earl B. 
Published: May 2005

AbstractCharacteristic differences in multiplet hyperfine structure observed in coupled 13C n.m.r. spectra of symmetrical o‐disubstituted benzene rings are explained on general grounds. Contrary to earlier proposals, the observation of this effect in unsymmetrical systems is not a suitable basis for corresponding 13C n.m.r. assignments unless the proton spectrum has been sufficiently analyzed. The 13C spectrum of piroxicam, an antiinflammatory agent, is assigned and some interesting relaxation properties are noted.
1H n.m.r. study of the self‐association of acetone phenylhydrazone by hydrogen bonding
Authors: Stassinopoulou C. I. , Petrou J. 
Published: May 2005

AbstractProton magnetic resonance dilution studies of acetone phenylhydrazone were carried out in n‐heptane, carbon disulphide and hexachlorobutadiene solutions. Equilibrium constants and enthalpy values for the predominant self‐associated species are reported. Linear trimeric aggregates predominate in n‐heptane solutions. The monomeric units are associated by intermolecular hydrogen bonding of the NH proton to the iminic nitrogen. The enthalpy per hydrogen bond is 10.04 kJ (2.4 kcal). In carbon disulphide and hexachlorobutadiene solutions complexation of acetone phenylhydrazone with the solvent competes with self‐association.
Nuclear magnetic resonance of oriented molecules in lyotropic liquid crystalline media: p‐cresol
Authors: Long Robert C. , Goldstein J. H. 
Published: May 2005

AbstractProton‐proton distance ratios and order parameters for partially oriented p‐cresol in a lyotropic mesophase derived from potassium laurate are obtained. The order parameters are the largest yet found for an ordered solute in a nematic‐like lyotropic system. The dipolar couplings and structural data were independent of the rotational potential from 0–200 cal mol−1.
Etude Conformationnelle par Résonance Magnétique Nucléaire Protonique des Dérivés de la O‐Isopropylidène‐2′,3′ Adénosine
Authors: Gaudemer Alain , Nief François , Pontikis Renée , Zylber Jean 
Published: May 2005

AbstractLes états conformationnels de plusieurs dérivés de la O‐isopropylidène‐2′3′ adénosine différante par la nature des substituants en C‐5′, C‐8 et N‐6 ont été déterminés à partir des données de RMN du proton, δ,3J et de mesures d'effet nucléaire Overhauser. Les variations conformationnelles observées résultent d'interactions spécifiques entre la partie sucre et la base purique et, d'autre part, d'autre part, d'effets de solvants.
NMR‐daten substituierter 1,2‐diphospholane sowie des 1,5‐diphosphabicyclo[3.3.0]octans und seiner p‐derivate
Authors: Issleib K. , Thorausch P. , Meyer H. 
Published: May 2005

AbstractAnhand von 13C‐ und 31P‐Spektren wird die Struktur 1‐ sowie 2‐substituierter 1,2‐Diphospholane, des 1,5‐Diphosphabicyclo[3.3.0]octans und dessen P‐Derivate ermittelt. Die 31P‐chemischen Verschiebungen zeigen für letztere eine zusätzliche sterisch bedingte Wechselwrikung der Phosphoratome. Sämtliche Verbindungen sind innerhalb der NMR‐spektroskopischen Nachweisgrenze sterisch einheitlich.
Carbon‐13 n.m.r. investigation of 2‐arylaminothiazolines and analogous thiazines, thiazepines and their amides
Authors: Sohár P. , Fehér G. , Toldy L. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of 2‐arylaminothiazoline, ‐thiazine and ‐thiazepine derivatives, and also those of some N‐substituted isomeric pairs were recorded and assigned. The structure of the individual isomers, which as a result of contradictory spectroscopic data had earlier been ambiguous, was established. In addition, the tautomeric structure of some N‐unsubstituted compounds was determined.
Carbon‐13 NMR studies. 73—carbon‐13 spectra of several 10‐methyl‐trans‐decalins. Further definition of the deshielding antiperiplanar γ effect
Authors: Ayer W. A. , Browne L. M. , Fung S. , Stothers J. B. 
Published: May 2005

AbstractThe 13C spectra of a series of 21 10‐methyl‐trans‐decalins have been recorded to explore in greater detail the deshielding antiperiplanar γ effects found earlier in a few of these derivatives. From the data for the series complete assignments for each compound were obtained, permitting an analysis of the shielding effects of the methyl and hydroxyl groups.
Natural‐abundance lithium‐6 NMR spin–lattice relaxation in some simple organolithium compounds
Authors: Wehrli F. W. 
Published: May 2005

Abstract6Li, 7Li and 13C spin–lattice relaxation and NOE data are reported for methyllithium, butyllithium and phenyllithium with 6Li T1 values found in the order of tens of seconds and their relaxation 2–3 orders of magnitude less efficient than that for 7Li. The data indicate that 6Li is substantially relaxed by the intramolecular 6Li–1H mechanism, whereas both quadrupolar and 6Li–7Li dipolar relaxation are minor processes. The non‐linearity of the Arrhenius curve for Me6Li is compatible with a small spin–rotation contribution. Since 6Li in solution behaves essentially as a spin‐1/2 nucleus, it represents, in spite of its lower magnetic moment and overall sensitivity, an attractive alternative to 7Li NMR.
Carbon‐13 NMR studies of twenty‐four methyl‐substituted morpholines
Authors: Nilsson Bertil , Hernestam Sven 
Published: May 2005

AbstractCarbon‐13 NMR spectra of all the isomers of monomethyl‐, 2,3‐, 2,5‐, 2,6‐, 3,5‐dimethyl‐, 2,3,5‐, 2,3,6‐trimethyl‐ and 2,3,5,6‐tetramethylmorpholine have been obtained at both ambient (25 °C) and low temperature (∼ −100 to −120 °C). The ring carbon shifts appear to be additive with respect to the position of the methyl groups. A good correlation between predicted and experimental shift values was obtained (r = 0.9989). The values were used in an attempt to assign, conformationally, the ‘all cis’ isomer 2,3,5,6‐tetramethylmorpholine, which from 1HNMR spin–spin coupling studies has been unsuccessful. Methyl carbon shifts to high field were found for axially oriented carbons. The extracted ‘steric shift’ values for such carbons were compared to their corresponding proton shift data.
The calculation of 2J(HH) couplings in benzyl groups
Authors: Abraham R. J. , Bakke J. M. 
Published: May 2005

AbstractThe results of FPT/INDO theory together with the observed 2J(HH) coupling in benzyl groups (Ph · CH2X) leads to a simple equation 2J(HH) = A+B cos θ+C cos 2θ where θ is the C.C.C.X dihedral angle, and X = C,H. The extension to other X substituents can be obtained from additivity rules.
Application of artificial intelligence for chemical inference. XXV. A computer program for automated empirical 13C NMR rule formation
Authors: Mitchell Tom M. , Schwenzer Gretchen M. 
Published: May 2005

AbstractA computer program which generates empirical rules associating 13C NMR shifts with local structural environments is described. The program uses a heuristic method to search for common structural features for those carbon atoms exhibiting similar shifts. Rules have been generated by our program from a combined set of acyclic amine and paraffin data. Examples of these rules are presented, and their performance as a tool for structure elucidation is examined.
Some self‐consistent perturbation calculations of 15N13C coupling constants
Authors: Khin Tun , Webb G. A. 
Published: May 2005

AbstractSelf‐consistent perturbation calculations within the INDO framework are reported for 63 15N13C coupling constants. Examples are presented for which each of the contact, orbital and dipolar terms provides the dominant contribution to the observed coupling constant. In general, good agreement with the experimental data is obtained when the integral products SN2(O)SC2(O) and 〈r−3〉N〈r−3〉C take the values 14.480 au−6 and 2.446 au−6 for 1J(15N13C), and the corresponding values of 10.444 au−6 and 17.664 au−6 for 1J(15N13C). All 19 of the 1J(15N13C) couplings considered are predicted to have a negative sign.
Bulky alkyls and amides of main group 5 elements II. Rotational barriers in phosphorus compounds containing bulky groups
Authors: Goldwhite Harold , Power Philip P. 
Published: May 2005

AbstractThe group [(CH3)3Si]2CH is effectively bulkier than the (CH3)3C group in inhibiting rotation about the PC bond in R2PCI compounds. In phosphonamidous chlorides, RP(CI)NR2′, increasing the bulk of the groups at nitrogen, e.g., from CH3 to (CH3)2CH to (CH3)3Si, increases the rotational barriers about the PN bond; however, changing R from (CH3)3C to [(CH3)3Si]2CH increases the barrier, which is a reversal of the trend earlier observed. It is suggested that these very bulky silylated groups represent limiting cases of steric interference.
A carbon‐13 nuclear magnetic resonance spectral data base and search system
Authors: Dalrymple D. L. , Wilkins C. L. , Milne G. W. A. , Heller S. R. 
Published: May 2005

AbstractA data base containing approximately 4000 13C nuclear magnetic resonance spectra has been assembled. The spectra have been evaluated and all the corresponding compounds have been registered by the Chemical Abstracts Service (CAS). The data base is available to the international scientific community on magnetic tape or microfiche and is also the basis of a search system operating upon an international computer network.