bluuebunny/crossref_metadata_2025_split huggingface dataset:
ESR of cation radicals of phenothiazine derivatives
Authors: Motten Ann G. , Chignell Colin F. 
Published: May 2005

AbstractPhenothiazines are of interest as model heterocyclic compounds and also as pharmacological agents with a wide spectrum of biological activities. Cation radicals derived from six phenothiazine derivatives including phenothiazine, 2‐chlorophenothiazine, promazine, chlorpromazine, promethazine and trimeprazine have been studied in aqueous solution by electron spin resonance. Their high‐resolution electron spin resonance spectra have been fully analysed, and hyperfine splitting parameters have been compared with those obtained in other solvent systems where available. Previously undetected hyperfine splittings of about 0.2–0.4 G from γ‐protons on the alkyl chain were observed for promazine, promethazine and, possibly, chlorpromazine.
A 15N NMR study of some fused polyaza heterocyclic ring systems
Authors: Kaczmarek L. , Nantka‐Namirski P. , Stefaniak L. , Webb G. A. , Davoust D. , Basselier J. J. 
Published: May 2005

Abstract15N NMR spectroscopy was used to distinguish between isomers and to characterize some series of novel fused polyaza heterocyclic ring systems. Support for the assignments was provided by means of some INDO/S‐SOS shielding calculations. Previously observed shielding trends, as a function of nitrogen type, are reproduced in the present set of molecules.
13C NMR spectroscopy of functionalized alkenyl and cycloalkenyl cyclopropanes
Authors: Chalchat J. C. , Garry R. Ph. , Lacroix B. , Michet A. 
Published: May 2005

AbstractThe 13C NMR spectra of ninety‐eight functionalised alkenyl and cycloalkenylcyclopropanes are described. The chemical shifts of specific carbon atoms, and the evaluation of certain pairwise contribution parameters between the substituents, provide information on the structure of the considered compounds.
13C NMR data bank techniques as analytical tools
Authors: v. d. Lieth C. W. , Seil J. , Köhler I. , Opferkuch H. J. 
Published: May 2005

AbstractVarious applications of computer programs which allow the automatic use of spectral and structural information from the SPEKTREN 13C NMR data bank are presented. A method of classifying clusters in a distribution of shifts belonging to the same substructure code is described and the reliability of the prediction of spectra is discussed. The influence of the size of the ‘shift window’ for spectral match was tested. The usefulness of the combination of spectroscopic and substructural information in various ways is illustrated, and the integrity of the used data base is tested with different methods.
NMR study of molecules in anisotropic systems. III—Structure and orientation of 1a,2a,3e,4e,5e,6a‐hexachlorocyclohexane in a nematic liquid crystal determined from low‐temperature experiments
Authors: Fujiwara Hideaki , Shimizu Naoto , Takagi Tatsuya , Sasaki Yoshio 
Published: May 2005

Abstract1H NMR spectra of 1a,2a,3e,4e,5e,6a‐hexachlorocyclohexane (γ‐BHC) have been measured in a nematic solution of ZLI2081 at low temperatures to prevent exchange broadening. The spectra were analysed and direct couplings determined. The six‐membered ring is most favourably oriented parallel to the solvent molecule. The principal axes of the order matrix differ from those of the moment of inertia, and the difference is explained as being due to the steric effect of the three axial chlorine atoms. The molecular structure of γ‐BHC in nematic solution is found to differ from that calculated from the MNDO MO method, but resembles that in the crystal determined by x‐ray spectrometry.
Application of two‐dimensional NMR spectroscopy to the analysis of the proton NMR spectrum of sparteine and its lactams
Authors: Gołȩlebiewski W. Marek 
Published: May 2005

AbstractCombined application of two‐dimensional 1H–1H homonuclear chemical shift correlation, two‐dimensional J‐resolved 1H NMR measurements and double resonance experiments permitted the specific assignment of the signals in the 1H NMR spectra and of the 1H–1H coupling constants of sparteine and its 2‐, 15‐ and 17‐oxo and 2,17‐dioxo derivatives. The results provide information on the conformation of these alkaloids.
Conformational studies on some phthalideisoquinoline derivatives
Authors: Kövér Katalin E. , Kerekes P. 
Published: May 2005

AbstractThe molecular conformation of phthalideisoquinoline derivatives was studied by 1H NMR methods. For the qualitative determination of the conformational preferences, proton relaxation times, 1D and 2D NOE experiments were applied. Our proposals were supported by the calculation of the effects of ring currents.
Conformational analysis. XXVII—A 1H and 13C NMR conformational study of cis‐ and trans‐annelated 2‐p‐nitrophenyl‐4,5‐ and ‐5,6‐tetramethyleneper‐hydro‐ and 2‐p‐chlorophenyl‐4,5‐ and ‐5,6‐tetramethylenedihydro‐1,3‐oxazines
Authors: Pihlaja Kalevi , Mattinen Jorma , Bernáth Gábor , Fülöp Ferenc 
Published: May 2005

AbstractThe 400 MHz 1H NMR spectra of cis‐ and trans‐annelated 2‐p‐nitrophenyl‐4,5‐ and ‐5,6‐tetramethyleneperhydro‐ and 2‐p‐chlorophenyl‐4,5‐ and ‐5,6‐tetramethylenedihydro‐1,3‐oxazines were recorded. The AMKX subspectra due to the protons at C‐4, C‐5 and C‐6 were analysed. Both cis‐ and trans‐annelated an equatorial 2‐p‐nitrophenyl group, as concluded from the values of their vicinal coupling constants and those in some simple model compounds, in agreement with the information given by 13C NMR and low‐temperature experiements. Correspondingly, trans‐2‐p‐chlorophenyl‐4,5‐ and ‐5,6‐tetramethylenedihydro‐1,3‐oxazines exist in anancomeric conformations; the cis isomers, however, are equilibrium mixtures of the N‐ or O‐eq and N‐ or O‐ax forms where the latter predominate, as shown by vicinal H, H coupling constants, 13C chemical shifts and low‐temperature experiments.
Synthesis and NMR analysis of isotopically enriched methanol
Authors: Walker T. E. , Wageman W. E. 
Published: May 2005

AbstractFour isotopomers of methanol were prepared enriched with 13C, 12C, and deuterium, including [13C, 2H4]methanol, [13C]methanol, [12C, 2H4]methanol and [12C]methanol. These compounds were analysed by proton NMR and by deuterium and 13C NMR, both proton coupled and decoupled. The spectra are useful for calculating the isotopomer distribution and for determining the percentage enrichment in the labeled positions, for which each spectrum provides unique information. A variety of coupling constants and isotope shifts are also reported.
1H NMR investigation of 10‐dimethylaminononafulvene
Authors: Otter Albin , Neuenschwander Markus , Kellerhals Hans Peter 
Published: May 2005

AbstractThe 1H NMR spectrum of 10‐dimethylaminononafulvene (2) has been analysed under high‐resolution conditions at low temperature. Chemical shifts and 27 non‐zero J values are reported. None of the parameters are significantly influenced by changes in solvent or temperature. The results indicate that 2 is not planar, and contains two sterically very different ring segments: a nearly planar (E)‐configurated dienamine system consisting of atoms N—(C‐10)—(C‐9)—(C‐8)—(C‐7) is linked to a triene system deviating strongly from planarity.
13C and 31P NMR spectra of 1‐diethylphosphono‐1‐hydroxycycloalkanes
Authors: Buchanan G. W. , Bourque K. , Seeley A. 
Published: May 2005

Abstract13C and 31P NMR chemical shifts and 13C‐31P couplings are reported for a series of thirteen 1‐diethylphosphono‐1‐hydroxycycloalkanes and their alkyl derivatives with carbocyclic ring sizes varying from four to twelve.
1J(CC) and 3J(CC) coupling constants in monosubstituted anilines. Additivity of substituent effects on carbon–carbon couplings
Authors: Sándor Péter , Radics Lajos 
Published: May 2005

AbstractIsotropic carbon–carbon coupling constants over one and three chemical bonds have been measured in ortho‐, meta‐ and para‐substituted anilines, C6H4NH2X (X = F, Cl, Br, I, OCH3, NH2, NO2, CN, COOCH3, CH3), in natural abundance. The experimental data are compared with J(CC) values calculated by assuming additivity of substituent coupling increments. Additivity conditions are discussed. Non‐additivities are interpreted, on a qualitative level, in terms of mesomeric and inductive interactions between the substituents.
15N NMR: Iminothiol‐thioamide tautomerism of 2‐mercaptobenzazoles and 1‐methyl‐2‐mercaptoimidazole
Authors: Balestrero R. S. , Forkey D. M. , Russell J. G. 
Published: May 2005

Abstract15N NMR spectra of a number of 2‐mercaptoazoles were obtained and the position of the iminothiol‐thioamide prototropic tautomeric equilibrium was determined. Because of the large chemical shift difference of ca 100 ppm between the iminothiol and thioamide nitrogen atoms, the 15N chemical shifts of the S‐methyl and N‐methyl analogs of each tautomer provided reasonable chemical shift models for the same nitrogen atom in the tautomers. Only a small correction for an N‐methyl effect was required.
Variable‐temperature and‐concentration 1H and 7Li NMR studies of solutions of hexameric iminolithium compounds, (R1R2CNLi)6
Authors: Barr Donald , Snaith Ronald , Mulvey Robert E. , Wade Kenneth , Reed David 
Published: May 2005

AbstractVariable‐temperature 7Li and proton NMR spectra of four hexameric (in the solid state) iminolithium compounds, (R1R2CNLi)6 [where R1 = Me2N,R2= Ph (1), R1 = R2 = Me2N (2), R1 = But, R2 = Ph (3) and R1 = R2 = But (4)], recorded for toluene‐d8, solutions of differing concentrations, are described, and the results are discussed with respect to known solid‐state structures. Complex equilibria, probably involving trimeric units and higher aggregates than hexamers, have been detected at low temperatures for solutions of 1 and 2, although similar equilibria do not occur, or are too rapid to detect even at the lowest temperatures attainable, for solutions of 3 and 4.
Solid‐state13C NMR study of drugs: Aspirin
Authors: Chang Ching‐Jer , Díaz Luis E. , Morin Frederick , Grant David M. 
Published: May 2005

AbstractNatural abundance13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high‐power decoupling, cross‐polarization and magic angle spinning. Solid‐state NMR of aspirin had excellent sensitivity compared with liquid‐state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non‐protonated carbons. The solid‐state13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic.The solid‐state13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.
1H, 13C, 17O and 33S NMR investigation of some cyclohexyl phenyl sulphides, sulphoxides and sulphones
Authors: Duddeck Helmut , Korek Uwe , Rosenbaum Doris , Drabowicz Jozef 
Published: May 2005

AbstractThe 1H and 13C NMR signals of cyclohexyl phenyl sulphides, sulphoxides and sulphones were almost completely assigned, and the effects of diastereotopism in cis‐4‐tert‐butylcyclohexyl phenyl sulphoxide were rationalized. Substituent effects on the 17O chemical shift of numerous sulphoxides and sulphones are discussed. An unusual paramagnetic γ gauche effect on the 33S nucleus was detected in cis‐4‐tert‐butylcyclohexyl phenyl sulphone.
Reinvestigation of the structural assignment of signals in the 1H and 13C NMR spectra of the flavone apigenin
Authors: Van Loo Piet , De Bruyn André , Buděšínský Miloš 
Published: May 2005

AbstractThe assignment of some 1H and 13C NMR chemical shifts of apigenin have been uncertain and even contradictory. A reinvestigation with recent NMR techniques has led to a new set of 13C NMR parameters and confirmed the accepted 1H NMR data.
15N NMR investigation of the tautomeric equilibria of some 1,2,4‐triazoles and related compounds
Authors: Bojarska‐Olejnik Elzbieta , Stefaniak Lech , Witanowski Michal , Webb Graham A. 
Published: May 2005

Abstract15N NMR shielding data for some 3‐methoxy‐1,2,4‐triazoles and related triazolones are reported. Assignments are given with the assistance of some INDO/S parameterized SOS shielding calculations. From the 15N NMR shielding results it is possible to give a quantitative account of some potential prototropic tautomeric equilibria.
Carbon‐13 NMR studies in the polycyclic hydrocarbon series. A new method for the identification of carbons α to a carbonyl group. Complete assignment of the 13C NMR spectra of several cis‐decalins, cis‐decalones, cis‐hydrindanones and 13α,14α‐ and 13β,14β‐steroids
Authors: Gramain J. C. , Quirion J. C. 
Published: May 2005

AbstractA new 13C NMR method based on solvent effects allows the identification of carbon atoms α to a carbonyl group. With a simple change in solvent from CDCl3 to CDCI3‐dioxane (1:4), the 13C absorption for all earbons except those α to the carbonyl group in the compounds under study were displaced to lower field by 0.2–0.5 ppm. The α‐carbon absorptions either remained unchanged or were shifted to higher field by ca 0.1 ppm. The validity of the method has been checked on compounds with fully assigned 13C NMR spectra (trans‐decalones and steroids). Moreover, no modification of these solvent shifts due to the presence of other common functional groups (double bond or OH) was observed. This new technique, together with existing ‘classical’ methods (‘off‐resonance’ spectra, substituent effects) enables the complete interpretation of the 13 C NMR spectra of five cis‐decalins and cis‐decalones to be made. The spectra of three cis‐hydrindanones which have not been previously described were also fully interpreted.The same method allows the complete spectral assignment of the 13C NMR spectra of six steroids of unnatural configuration in the 13α,14α‐ and 13β,14β‐androstane series, for which no data were previously available.
On‐line NMR in process engineering
Authors: Neudert R. , Ströfer E. , Bremser W. 
Published: May 2005

AbstractThe basis of the evaluation of chemical processes is a comprehensive knowledge about the concentration profiles of the reactants as a function of time. Normally, analytical samples are taken from the reaction medium, with the disadvantage that the analysis does not occur on the reaction time scale and the reaction equilibrium itself is disturbed. For this reason, an on‐line analytical system based on the coupling between an NMR spectrometer and a chemical reactor was developed.The applicability of the system is demonstrated on a Wittig reaction, the last step in the synthesis of retinoic acid. 31P NMR was employed for the detection of the time dependent concentration of phosphorylated reaction components. The consequences of the results with respect to a change of the chemical process are discussed.
Quantitative analysis of pyrrolizidine alkaloid mixtures from Senecio vulgaris by carbon‐13 nuclear magnetic resonance spectroscopy
Authors: Pieters L. A. C. , Vlietinck A. J. 
Published: May 2005

AbstractA 13C NMR method has been developed for obtaining simultaneously structural and quantitative information on mixtures of pyrrolizidine alkaloids from Senecio vulgaris L. (Compositae). The samples contained seneciphylline, senecionine, retrorsine and the corresponding E geometrical isomers, spartioidine, integerrimine and usaramine. The spin‐lattice relaxation times were measured and, after establishing the instrumental requirements for quantitative 13C FT NMR, all the alkaloids of the mixture could be determined. Quantitative 1H and 13C FT NMR analyses were carried out, and the advantages and limitations of these methods are discussed.
High‐resolution proton magnetic resonance spectra of morphine and its threeO‐acetyl derivatives
Authors: Neville George A. , Ekiel Irena , Smith Ian C. P. 
Published: May 2005

AbstractHigh‐resolution1H NMR (500 MHz) spectra were recorded for morphine, 3‐O‐acetylmorphine, 6‐O‐acetylmorphine and diacetylmorphine (heroin). Complete assignment of all proton resonances was made for these substances following determination of accurate chemical shift and coupling data by spectral simulation of all tightly coupled proton resonance patterns. Chemical shifts and proton couplings are discussed in terms of the conformation of rings C and D. From a varied collection of morphine analogs, torsion angles for ring D protons were obtained from crystallographic studies. The corresponding coupling constants were calculated, they demonstrate similar conformation of the ring D for the compared morphine compounds.
ENDOR studies of semiquinone radical ions in liquid crystalline solutions
Authors: Kirste Burkhard 
Published: May 2005

AbstractStudies of a series of substituted benzo‐, naphtho‐, anthra‐ and phenanthrene‐semiquinones, benzil semidione and Wurster's blue perchlorate by ENDOR spectroscopy in liquid crystalline solutions are reported. Sufficient solubility of the radical anions is achieved by using lipophilic counter ions such as benzyltrimethylammonium. The effects of ion pairing were investigated, particularly in the case of benzil semidione, which can adopt cis or trans configurations. The anisotropic hyperfine shifts observed in nematic or smectic phases are interpreted by means of calculated dipolar hyperfine tensors. A detailed picture of the alignment of the radical ions in liquid crystalline solvents is obtained. The calculated hyperfine tensors are checked for consistency with experiment, and in some cases compared with measurements in solid solution.
Carbon‐13 NMR spectra of some pseudoguaianolides
Authors: Delgado Guillermo , Alvarez Laura , Huerta Eduardo , de Vivar Alfonso Romo , Mata Rachel 
Published: May 2005

AbstractThe 13C NMR resonances of a series of pseudoguaianolides are reported, which have been assigned on the basis of multiplicities, chemical shift theory and comparison with related substances.
Nuclear magnetic resonance study of the configurational equilibria of ranitidine in solution
Authors: Geraldes Carlos F. G. C. , Gil Victor M. S. , Teixeira M. Helena S. F. , Teixeira F. 
Published: May 2005

AbstractThe E/Z configurational equilibrium of the nitroethylenic moiety of the antiulcer agent ranitidine was studied in aqueous solution and in DMSO‐d6 and CDCl3 using 1H and 13C NMR spectroscopy. In aqueous solution the room temperature E/Z isomerization of the unprotonated nitroketenediamine moiety is fast on the NMR time scale, but becomes slow for the species protonated at this moiety owing to intramolecular hydrogen bonding between the nitro group and a neighbouring NH2R+ group. In DMSO‐d6 a free energy of activation of the order of 70 kJ mol−1 was estimated for the E/Z isomerization of the unprotonated moiety of ranitidine, in good agreement with values previously found for 2,2‐disubstituted nitroethylene model compounds.
17O NMR studies of torsion angle relationships in aryl alkyl ketones and aromatic aldehydes
Authors: Boykin D. W. , Balakrishnan P. , Baumstark A. L. 
Published: May 2005

Abstract17O NMR spectroscopic data, at natural abundance, in acetonitrile at 75 °C were obtained for a series of phenyl alkyl and cycloalkyl ketones, benzophenone, methyl alkyl ketones, three fused‐ring aryl ketones and a series of variously hindered aromatic aldehydes. The trend in chemical shifts for the relatively unhindered alkyl aryl ketones is a general increase in shielding with increasing size of the alkyl group. However, when steric hindrance becomes significant, torsion angle rotation occurs and deshielding is observed. Cyclopropyl ketones show much larger shielding effects than their isopropyl analogs. Torsion angles for aryl ketones and aromatic aldehydes are estimated using an indirect method based on previous results from electronically similar hindered ketones.
Significance testing of lanthanide shift reagent data
Authors: Ribó Josep M. , Valera GeníS 
Published: May 2005

AbstractThe use of weighted agreement factors in the significance testing of lanthanide‐induced shift analysis is physically meaningless, and can manipulate the resulting significance values, as confirmed by the results found with two compounds. The Hamilton ℛ factor ratio significance test and the jacknife test are compared for these compounds. The ℛ ratio test is more easily applied; the jacknife test does not show any clear advantage and is more sensitive to changes originating from the use of weighted agreement factors.
Study of the prototropic tautomerism of 8‐azatheophylline by 13C and 15N NMR spectroscopy
Authors: L'abbé Gerrit , Persoons Marie‐Anne , Toppet Suzanne 
Published: May 2005

AbstractComparison of the 13C and 15N NMR spectra of 8‐azatheophylline with those of its three methylated derivatives and other model compounds from the literature showed that 8‐azatheophylline exists to the extent of 80% in the N‐2 tautomeric form in DMSO solution.
Origins of phase anomalies in 13C FT NMR spectra
Authors: Anet Frank A. L. , Zheng Li Kao , Zhihong Tan 
Published: May 2005

AbstractSome controversy exists on the origin(s) of phase anomalies observed in 13C FT NMR spectra. Two separate explanations, based on either echo or sampling effects, have been proposed by previous workers. We now show experimentally that these two effects can occur separately or together and, in the latter case, the effects can interfere with one another. Methods to ameliorate or remove phase anomalies are briefly reviewed.
1H and 13C nuclear magnetic resonance study of 1,3‐dipyridylthioureas for chemical shift assignments and conformational analysis
Authors: Sudha L. V. , Sathyanarayana D. N. , Bharati S. Narasimha 
Published: May 2005

AbstractA study of molecular conformation by 1H and 13C NMR methods of three 1,3‐dipyridyl thioureas namely, 1,3‐di(2‐pyridyl)thiourea (1), 1,3‐di(3‐pyridyl)thiourea (2), 1‐(2‐pyridyl)‐3‐(3‐pyridyl)thiourea (3), and also of 1‐phenyl‐3‐(2‐pyridyl)thiourea (4) and 1,3‐diphenylthiourea (5), included for the sake of comparison, was carried out. Evidence was obtained that 3 and 4 exist in solution solely in one form, in an internally hydrogen bonded E,Z conformation, whereas 1, 2 and 5 exist in two (or more) rotamer forms. The data reveal an interesting dynamic exchange phenomenon occurring in 1 between two intramolecularly hydrogen bonded conformers. The 1H and 13C chemical shifts, 1H,1H and 13C,1H coupling constants are reported. The 13C and 1H chemical shifts are correlated with the electron densities calculated by the CNDO method.
13C NMR spectra of some sulphur dioxide—aromatic amine complexes
Authors: De Faria D. L. A. , Santos P. S. 
Published: May 2005

AbstractThe 13C NMR spectra of equilibrium mixtures formed between sulphur dioxide and N‐methylbenzenamine, N,N‐dimethylbenzenamine and N,N‐diethylbenzenamine were obtained. The analysis of the spectral data indicates that the interaction of the amines with the Lewis acid occurs by means of the lone pair mainly localized on the nitrogen atom, and that the complexes can be considered as labile on the time scale of the experiment.
ESR and theoretical study of tetrathiofulvalene and dibenzotetrathiofulvalene and their radical cations
Authors: Hibbert D. Brynn , Hamedelniel Abdelrazik E. , Sutcliffe Leslie H. 
Published: May 2005

AbstractThe three semi‐empirical methods MNDO, AM1 and MINDO/3 have been used to determine geometries, ionization potentials and spin densities of tetrathiofulvalene, dibenzotetrathiofulvalene and their radical cations. ESR measurements of the cation radicals both in solution and the solid states provided experimental spin densities. A comparison is made between calculated and experimental data; it appears that MINDO/3 is superior for the calculation of spin densities.
13C NMR Data [δ(13C), 1J(C,H), 1J(C,C)] of some bicycloalkenes
Authors: Benn R. , Butenschön H. , Mynott R. , Wisniewski W. 
Published: May 2005

AbstractThe 13C shifts of the bicyclo[3.2.0]alkenes 1‐7, spiro[2.4]hepta‐4,6‐diene (8) and the bicyclo[3.3.0]octenes 9 and 10 have been assigned via one‐ and two‐dimensional INADEQUATE experiments. The values of 1J(C,H) and 1J(C.C) of 1‐10 are also reported.