bluuebunny/crossref_metadata_2025_split huggingface dataset:
cis‐trans‐and Intramolecular enol‐enolic equilibrium of β‐ketoaldehydes
Authors: Noy R. S. , Gindin V. A. , Ershov B. A. , Kol'tsov A. I. , Zubkov V. A. 
Published: May 2005

AbstractTautomerism of aromatic β‐ketoaldehydes p‐XPhCOCH2CHO (1, X = NMe2, OMe, Me, H, Br, NO2), aliphatic β‐ketoaldehydes and benzoylacetaldehyde RCOCH2CHO (2, R = Me, i‐Bu, t‐Bu, Ph), RCOCH(Me)CHO (3, R = Me, Et, i‐Pr) and methyl 2‐formylpropionate MeOCOCH(Me)CHO (4) has been studied by the 1H NMR technique. In basic solvents both cis‐ and trans‐enol forms of these compounds co‐exist. trans‐Enolisation, which occurs exclusively at the formyl group, is most favoured in compound (4) and least favoured in compounds (1) and (2). The increasing electron‐attracting property of the substituent X in the aromatic β‐ketoaldehydes (1), as well as increasing solvent basicity in the series propanediol‐1, 2‐carbonate, acetone < dimethylformamide < dimethylacetamide < pyridine, also shifts the equilibrium towards the trans‐enol form. The trans‐enol form is absent in aprotic solvents of low basicity such as CCl4, C2HCl3 and toluene. The thermodynamic parameters of the cis‐trans‐enol (C ⇌ T) and cis‐enol‐enolic (C ⇌ C') equilibria have been estimated from the temperature dependences. The transition from the cis‐to the trans‐enol form is accompanied by an entropy decrease of about 10 cal mol−1 degree−1. Nevertheless the trans‐enol form is stabilised due to its lower enthalpy. The cis‐trans‐enol equilibrium is determined by the relative strength of the intramolecular hydrogen bond in the cis‐enol form and the intermolecular hydrogen bonds with basic solvent molecules of the trans‐enol form.The enthalpy difference of the two cis‐enolic forms does not exceed 1.0 kcal/mol, in rough agreement with the data calculated by the CNDO/2 approximation. Polar solvents favour the hydroxymethyleneketone form (C) for both groups of compounds 2 and 3. The content of the hydroxymethyleneketone form is about the same within series 2 where R = Me, i‐Bu, Ph and is a little higher for the t‐Bu derivative. A decrease of temperature only slightly shifts the equilibrium of compounds 1 and 2 to the hydroxymethyleneketone form, while in the case of 2‐methyl‐β‐ketoaldehydes (3) this effect is markedly pronounced.
Carbon‐13 NMR spectra of fusicoccin and its derivatives
Authors: Radics L. , Kajtár‐Peredy M. , Casinovi C. G. , Grandolini G. , Rossi C. 
Published: May 2005

AbstractThe 13C NMR spectra of fusicoccin, some of its cometabolites and derivatives were studied. Using standard Fourier transform techniques, T1 relaxation time measurements and lanthanide shift reagents, the resonances of individual carbon‐13 nuclei were assigned.
Carbon‐13 nuclear magnetic resonance spectra. I—Monosubstituted adamantanes and adamantanones
Authors: Duddeck Helmut 
Published: May 2005

AbstractThe chemical shifts of 4ax and 4eq substituted adamantanones are compared with those calculated with the aid of a given additivity rule. It is found that both δ carbons are shielded with respect to the substituent. In contract to the situation for the y‐atoms, however, the δsyn atom is less shielded than the δanti atom. In most cases the additivity rule predicts the chemical shifts with an accuracy of approximately 1 ppm. Exceptions are carbon atoms 4 and 9 of the 4eq substituted adamantanones. In both cases the measured values are 4 to 6 ppm upfield. This can possibly be explained by an electronic interaction between the carbonyl group and the substituent.
Aziridines. IX—Mise en évidence du phénomène d'inversion de l'azote dans les aziridines secondaires par RMN de 13C
Authors: Martino R. , Mison P. , Wehrli F. W. , Wirthlin T. 
Published: May 2005

AbstractL'effet d'inversion de l'azote sur les déplacements chimiques en Résonance Magnétique Nucléaire de carbone‐13 a été observé avec la diphényl‐2,2‐aziridine, la diméthyl‐2,2 diphényl‐3,3 aziridine et la phényl‐2 méthyl‐2 aziridine, sous des conditions d'échange lent du proton du NH. De plus, nous avons pu déceler des variations de déplacements chimiques dǔes à un échange isotopique lent HD.
Long range 13C1H coupling constants. III—methylpyridines
Authors: Takeuchi Yoshito 
Published: May 2005

AbstractProton coupled carbon‐13 NMR spectra of eleven mono‐, di‐ and trimethylpyridines were analysed on a first order basis. The long range 13C1H coupling constants are similar to those observed for pyridine and cyanopyridines.
Carbon‐13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H‐azirines
Authors: Isomura Kazuaki , Taniguchi Hiroshi , Mishima Masaaki , Fujio Mizue , Tsuno Yuho 
Published: May 2005

AbstractCarbon‐13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H‐azirines. The higher field resonance of C‐2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C‐3 is indicated by a large J(13C‐3,H) value (242.5 Hz).
Carbon‐13 n.m.r. spectroscopy of some Strychnos alkaloids
Authors: Verpoorte R. , Hylands P. J. , Bisset N. G. 
Published: May 2005

Abstract13C N.m.r. spectra have been determined for strychnine and a series of fourteen derivatives. The assignments are based on previously established data and on off‐resonance decoupled spectra. The shifts resulting from the alterations in molecular structure are discussed and explained, in part, as a consequence of conformational changes. This detailed study indicates that changes are required in some previously published assignments.
Application of 13C and 15N spectroscopy to the study of electronic delocalization in NN bonds: Nitrosamines, hydrazones, triazenes and related protonated species
Authors: Gouesnard J. P. , Martin G. J. 
Published: May 2005

Abstract13C and 15N spectroscopies at natural abundance have been applied to the study of nitrogen lone‐pair delocalization in NN containing compounds: nitrosamines, nitramines, hydrazines, hydrazones and triazenes. Structure‐chemical shift correlations have been derived for nitrosamines; the 13C upfield effect of a γ substituent has been used for assigning the configuration of both diastereoisomers in N,N‐unsymmetrically substituted nitrosamines. Equations have been computed which permit the prediction of the electronic delocalization, expressed in terms of free enthalpy of activation ΔG, as a function of δ15N and of the length of the NN bond. 15N spectroscopy has also been applied to the study of the protonated species of nitrosamines and of acceptor‐donor complexes of nitrosamines with Lewis acids. The behaviour of such NN containing compounds is compared to that of amides.
An NMR structural study of 2‐fluoropyridine dissolved in a nematic solvent
Authors: Burnell E. E. , Marshall A. G. , Roe D. C. 
Published: May 2005

AbstractThe proton NMR spectrum of 2‐fluoropyridine partially oriented in a nematic phase has been analyzed, and the geometry of the proton and fluorine skeleton and the order matrix have been determined. The structure does not differ significantly from that of pyridine in a nematic solvent, and the largest positive order parameter axis lies approximately along the CF bond direction in the molecule.
Carbon‐13 nuclear magnetic resonance spectra and conformations of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis, syn,cis‐1,5‐cyclooctadiene diepoxide
Authors: Anet Frank A. L. , Easton N. Roy , Yavari Issa 
Published: May 2005

AbstractThe natural‐abundance 13C NMR spectra of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis,syn,cis‐1,5‐cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free‐energy barrier (ΔG≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol−1 from a line‐shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis‐1,5‐cyclooctadiene diepoxide exists in solution in chair (major) and in twist‐boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist‐boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.
Calculation of 1H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes
Authors: Vogler H. 
Published: May 2005

AbstractThe ring current and local anisotropic contributions to the 1H chemical shifts of [n]annuleno[m]annulenes and [n]annulenyl[m]annulenes with n, m = 12, 14, 18 and n, m = 13, 15 are calculated. The agreement between experimental and calculated shifts for the few known compounds is very good so that the predictions for the as yet unknown compounds are reliable. The effect of an annulene ring on the shifts of the protons at the other ring in these bicyclic compounds is discussed for several types of fusion of the two constituent annulenes.
1H‐, 31P‐ and 13C‐NMR spectra of some 2‐arylsulphonylamido‐2‐thiono‐5‐methyl‐1,3,2‐dioxaphospholanes
Authors: Barabás A. , Mureşan V. , Almási L. 
Published: May 2005

AbstractSome 2‐arylsulphonylamido‐2‐thiono‐5‐methyl‐1,3,2‐dioxaphospholanes (1), containing two chiral centres, give NMR spectra in which splittings of the 1H and 13C signals of the 5‐methyl substituent and of the 31P signal indicate that they exist in an approximately 70:30% ratio of two racemic mixtures, Z and E respectively, diastereomeric to each other. These splittings were invariably observed for compounds 1a, containing a monosubstituted sulphonylamido group (Y = H) and various substituents at position 4′ of the aryl group, X = H, CH3, OCH3, F, CI and Br. The methylenic protons in position 4 of the phospholane ring are diastereotopic and therefore magnetically non‐equivalent. Benzene‐induced shifts were measured for the Z isomers of compounds 1a, X = H, F and for compound 1b, containing an N‐disubstituted sulphonylamido group (Y = CH3) and X = H; the tentative interpretation of these shifts places the more shielded diastereotopic methylene proton on the same side of the ring as the 5‐methyl substituent. The HP and HH coupling constants indicate that the preferred conformation of the dioxaphospholane ring should be a ‘twisted envelopey’ shape with the 5‐methyl substituent in the equatorial position.
A13C NMR investigation of restricted rotation and dimerization inp‐substituted nitrosobenzenes
Authors: Cox Richard H. , Hamada Masao 
Published: May 2005

AbstractThe barrier to internal rotation in a series ofp‐substituted nitrosobenzenes has been determined by means of variable temperature13C NMR. Substituent (X) effects on the barrier are similar to those observed for acetophenones and benzaldehydes. In addition, dimerization of the nitrosobenzenes was observed at low temperature for X = CH3, CI and H. The barrier height is discussed in terms of contributions from resonance effects.
Prediction of proton magnetic resonance shifts: The dependence on hydrogen charges obtained by iterative partial equalization of orbital electronegativity
Authors: Gasteiger Johann , Marsili Mario 
Published: May 2005

AbstractProton chemical shifts correlate linearly with charges on hydrogen obtained by a method for iterative partial equalization of orbital electronegativity. The compounds studied comprise a wide variety of classes of molecules; all points fall on a single correlation line, showing the general importance of electronic effects in proton chemical shifts and the physical significance of the atomic charges. On the other hand, as there is no general correlation between charges on carbon and on hydrogen atoms, proton chemical shifts cannot be used as probes for charge densities on carbon atoms. Deviations from the correlation line can be attributed to anisotropy effects and provide an estimate for their magnitude.
The conformations of bicyclo[3.1.0]hexane derivatives by 1H and 13C NMR
Authors: Rees John C. , Whittaker David 
Published: May 2005

AbstractThe 1H and 13C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1‐methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C‐4.
14N nuclear quadrupole resonance in nicotinic acid derivatives
Authors: Kim N. S. , Bray P. J. 
Published: May 2005

AbstractNitrogen‐14 nuclear quadrupole resonance (NQR) spectra of nicotinic acid derivatives, known as antitumor agents, are reported and analyzed in the framework of the Townes and Dailey theory. A strong correlation exists between the charge difference σNC − π at the pyridinic nitrogen and the inhibition of acetylcholinesterase by nicotinic acid derivatives, in which the inhibition potency (pI50) increases as the charge difference σNC − π increases. There are significant differences between 14N NQR spectra for the pyridinic nitrogen sites of nicotinic acid and nicotinamide; these can be explained in terms of the differences in hydrogen bond lengths.
Carbon‐13 NMR spectroscopy of some pentacyclic triterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Ghosh Saroj , Ghosh Amitava , Barua A. K. 
Published: May 2005

AbstractCarbon‐13 NMR signal assignment of a number of polyoxygenated triterpenes of the olean‐12‐ene and urs‐12‐ene series, carried out by considering the changes in chemical shift produced by the change of oxygenation pattern(s), and using methyl oleanolate as a model, are reported.
Sulphur‐33 nuclear magnetic resonance studies of sulphur compounds with sharp resonance lines. 33S NMR spectra of some sulphones and sulphonic acids
Authors: Faure R. , Vincent E. J. , Ruiz J. M. , Léna L. 
Published: May 2005

Abstract33S NMR spectra have been obtained in the FT mode for some sulphones and sulphonic acids. The investigated compounds show narrow resonance lines. In the case of sulphones, the range of 33S chemical shifts is sufficiently wide, i.e. the effects due to changes in substituents are significant enough to allow further use of the 33S NMR of sulphones for quantitative analysis in petroleum chemistry.
Carbon‐13 NMR spectra of a series of para‐substituted phenyl isothiocyanates. Linear free energy relationships for carbon‐13 substituent chemical shifts
Authors: Jones Ronald G. , Allen Grace 
Published: May 2005

AbstractCarbon‐13 chemical shifts are reported for 16 para‐substituted phenyl isothiocyanates measured at 1 and 10 mol % in chloroform‐d solution. Data for the NCS group were not obtained at 1 mol %, but concentration effects for the other resonances were negligible. Hammett, dual substituent parameter (DSP) and DSP‐nonlinear resonance (DSP‐NLR) analyses were used to evaluate substituent effects on the substituent chemical shifts (SCS) for the ipso‐carbon (C‐1), C‐2, and the NCS carbon atoms. A good Hammett correlation was observed for C‐1 (νp+ = 8.1 ppm, r = 0.98 at 1 mol %) but was improved for the higher order correlations with the following results, DSP:ρ I = 5.4, ρR° = 22.2, r = 0.998; DSP‐NLR: ρI = 5.6, ρR° = 20.5, ϵ = −0.22, r = 0.999. The 10 mol % data were very similar except the value of ϵ was −0.26 and confirms the phenyl‐bonded NCS moiety as a mild electron acceptor substituent. Hammett correlations were unsuccessful for the C‐2 data, but fairly good results were obtained from the higher order analyses. For the 1 mol % data, DSP: νI = 1.6, νR° = −2.0, r = 0.976; DSP‐NLR: νI = 1.8, νR° = −2.6, ϵ = 1.1, r = 0.982. Excellent correlations were obtained for the 10 mol % NCS carbon data. Hammett: νp° = 6.2, r = 0.997; DSP: νI = 5.9, νR° = 7.0, r = 0.997; DSP‐NLR: νI = 5.8, νR° = 7.6, ϵ = 0.25, r = 0.997. The positive ν values in these three correlations contrast the negative values usually observed for carbonyl and thiocarbonyl carbons, and more closely parallel results previously reported for the β‐carbon of styrenes and benzylidene anilines with para‐substituents in the aniline ring.
The use of lanthanide‐induced shifts for conformational and structural studies of (R)‐MTPA (α‐methoxy‐α‐trifluoromethyl‐α‐phenylacetic acid) esters. 2—Complexes of the (R)‐MTPA esters of 4‐tert‐butylcyclohexanols with Eu(fod)3
Authors: Vanhoeck L. , Bossaerts J. , Dommisse R. A. , Lepoivre J. A. , Alderweireldt F. C. 
Published: May 2005

AbstractIt is shown that the complexation of the (R)‐MTPA (α‐methoxy‐α‐trifluoromethyl‐α‐phenylacetic acid) ester ofcis‐4‐tert‐butylcyclohexanol with Eu(fod)3is very similar to that of the correspondingtrans‐ester and ketones with Eu(fod)3. Further evidence is provided that the MTPA moiety exists as two different rotamers. The LIS technique, used as a tool for structure and conformation elucidation, was found by means of a Monte Carlo error analysis not to be dependent on small experimental errors.
Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus
Authors: Rijo Patrícia , Fátima Simões M. , Rodríguez Benjamín 
Published: May 2005

AbstractThree labdane diterpenoids were isolated from an acetone extract of Plectranthus ornatus. Their structures, closely related to that of forskolin, were determined by NMR studies. Unambiguous and complete assignments of the 1H and 13C NMR chemical shifts for these substances are presented. The assignments are based on 2D shift‐correlated [1H, 1H‐COSY, 1H, 13C‐gHSQC‐1J (C,H), 1H, 13C‐gHMBC‐nJ (C,H) (n = 2 and 3)] and NOE experiments. Copyright © 2005 John Wiley & Sons, Ltd.
Habituation of the motion detectors of the crayfish optic nerve: Their relationship to the visually evoked defense reflex
Authors: Glantz Raymon M. 
Published: May 2005

AbstractExamination of sustaining units, dimming units, and motion detectors under stimulus conditions associated with defense reflex habituation revealed that only the motion detectors exhibit a response decrement with stimulus repetition. Motion detector habituation was specific to the retinal locus of the repetitive stimulus and thus can provide a basis for the spatially specific component of defense reflex habituation. When stimulated at low repetition rates (2‐‐4 min) the motion detectors exhibited a time course of habituation and spontaneous recovery similar to that observed behaviorally. At high repetition rates (20/mm) the motion detectors exhibited a more rapid rate of habituation than was observed for the defense reflex. Simultaneous recordings of motion detector and cheliped levatory muscle activity revealed consistently significant and frequently substantial positive correlations. Both defense reflex and motion detector habituation were transiently reversed by treatment with the GABA antagonist, picrotoxin (1.8 2.8 mg kg body weight). The action of picrotoxin is likely to be mediated via mechanisms controlling the general level of arousal. It was concluded that the response variations of motion detectors subjected to repetitive stimuli contribute to the habituation of the visually evoked defense refle.
The morphology of cricket giant interneurons
Authors: Mendenhall Barbara , Murphey R. K. 
Published: May 2005

AbstractAxonal iontophoresis of cobalt chloride was used to describe the morphology of the seven largest interneurons in the abdominal nervous system of the cricket Acheta domesticus. The somata of these neurons are all found in the terminal (5th) abdominal ganglion. This ganglion is derived from four primitive segmental ganglia (the 7th–10th primitive segments) and the morphology of the interneurons within this ganglion suggests that the neurons are derived from different primitive segments. Furthermore, some of the neurons appear to be serially homologous elements. Three aspects of the morphology support these suggestions: (1) soma position, (2) relative positions of commissural processes, and (3) the general shape and extent of dendritric fields.
Neuromuscular transmission in an insect visceral muscle
Authors: Orchard Ian , Lange Angela B. 
Published: May 2005

AbstractThe electrical properties of the muscles of locust oviduct have been examined using intracellular recordings. The muscle cells are both dye and electrically coupled. They possess a wide array of spontaneous electrical activity ranging from slow oscillations of membrane potential to action potentials. In addition to possessing spontaneous electrical activity, certain regions of the oviduct are under motor control. The amplitude of evoked excitatory junction potentials (EJPs) increased step wise revealing innervation from a maximum of three motor units. These EJPs underwent summation and facilitation, and reached a critical threshold at which point the membrane revealed an active response. Bath applied glutamate, aspartate, proctolin, and octopamine were tested for their ability to alter resting potential and EJPs. L‐glutamate (1.6 × 10−5 M and above) produced a dose‐dependent depolarization of membrane potential accompanied by a reduction in amplitude of EJPs. Although L‐aspartate resulted in similar effects, the concentrations required were higher than those for glutamate. Proctolin (6.3 × −11 M − 6.0 × 10−9 M) resulted in a dose‐dependent depolarization but had little or no effect on amplitude of EJPs. Application of D, L‐octopamine (3.2 × 10−5 M − 1.7 × 10−4 M) induced a small hyperpolarisation and a reduction in amplitude of EJP. It is suggested that contractions of locust oviduct appear to be regulated by a combination of a classical neurotransmitter such as glutamate, along with the neuromodulators octopamine and proctolin.
Differential time course of the response to axotomy induced by cut or crush in the leech AP cell
Authors: Matteoli Michela , Nencioni Brunetta , Pellegrino Mario 
Published: May 2005

AbstractThe time course of the reaction to axotomy in the leech AP cell was determined by measuring the duration of the spontaneous spikes at different times after the operation. The axotomy performed by section of the segmental roots containing the AP axon induced an increase of the spike duration, which persisted over 30 days. A different time course was found when the axotomy was performed by nerve crush: the changes in duration of the spontaneous spikes, which occurred during the early 2 weeks, were significantly reduced afterwards. Dye staining of some cells axotomized by crushing revealed that the reversion of the changes, which had been set up by axotomy, was in some cases concomitant with the reconnection between proximal and distal axon stumps. The section of a single axonal branch was never sufficient to affect the membrane properties of the AP cells.It is concluded that the changes observed in axotomized AP cells are not produced by simple axonal injury and that the maintainance of normal properties in the somatic membrane requires the presence of at least part of the distal axon arborization.