bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR study of the overall and internal motions of a semi‐rigid hydrocarbon
Authors: Gillies D. G. , Matthews S. J. , Sutcliffe L. H. 
Published: May 2005

AbstractAn extensive investigation has been made of the 13C NMR relaxation parameters of 2,4‐dicyclohexyl‐2‐methylpentane neat and in solution. Spin‐lattice relaxation times and nuclear Overhauser enhancements were measured as a function of temperature, concentration and radiofrequency. The results for all the carbons, except the methyls, can be interpreted by using a reduced spectral density which suggests that there is an isotropically rotating semi‐rigid backbone structure whose internal librations and vibrations reduce the amplitude of the spectral density. However, interpretation of the methyl group data required the addition of a discrete correlation time characteristic of the internal motion about a C3 axis. From dilution studies, the validity of using the two‐correlation time spectral density with S2 = 0 when the rate of overall motion approaches that of the internal motion was established, for the first time.
Electron spin resonance spectroscopy of free radicals containing sulphur linked to nitrogen
Authors: Preston K. F. , Sutcliffe L. H. 
Published: May 2005

AbstractThere is an abundance of information on closed‐shell compounds containing sulphur linked to nitrogen; much less, of course, is known about free radicals containing this moeity. This review describes the wide variety of these radicals, their remarkable stability, the characteristic values of their ESR parameters, their electronic structures and their potential applications.
Low‐temperature study of dynamic effects in tetramethyllimonene
Authors: Bigler P. , Müller C. , Bircher H. 
Published: May 2005

AbstractDynamic effects of tetramethyllimonene were studied at low temperatures. Nuclear Overhauser effects measured under optimized conditions at 223 K and the results of 2D correlation experiments allowed the identification of two conformers and the assignment of all the proton and carbon resonances. For the determination of exchange and relaxation rates the method of saturation transfer was applied. At temperatures below 223 K further dynamic effects were recognized. Structural information obtained experimentally was compared with the results of Allinger force field calculations.
1H and 13C NMR studies on the self‐association of retinoic acid
Authors: Waterhous D. Vincent , Muccio Donald D. 
Published: May 2005

AbstractThe monomer–dimer equilibrium of retinoic acid in carbon tetrachloride was studied by 1H and 13C NMR spectroscopy. The dimer dissociation constant at 24°C was determined to be 0.38 mM from a fit of the changes in the carboxylic acid carbon chemical shift as a function of concentration. The temperature dependence of the equilibrium constant obtained from the 13C NMR signals was used to determine the enthalpy (8.0 kcal mol−1) and entropy (12 cal mol−1 K−1) changes for the dimer dissociation process. These results were shown to be more precise than the values obtained from the carboxylic acid proton resonance.
Electron spin resonance study of polymeric charge‐transfer complexes
Authors: Palaniappan Srinivasan , Sathyanarayana Dixit N. 
Published: May 2005

AbstractPolymeric charge‐transfer complexes with different polymer donors and monomer acceptors were investigated by electron spin resonance spectroscopy. The spin concentrations, g‐values and line widths in the complexes have been determined. The concentration of the paramagnetic charge‐transfer complexes generally increased with increasing strength of the donor‐acceptor tendencies, and exhibited an exponential temperature dependence of spin concentration characteristic of semiconductors. The paramagnetic charge‐transfer complexes were finally transformed into a diamagnetic product; this was confirmed by electronic spectroscopy.
Studies on the benzoxazine series. Part 3—Preparation and13C NMR structural Study of γ Effects of SomeN‐substituted 3,4‐dihydro‐2H‐1,3‐benzoxazines
Authors: Neuvonen Kari , Pihlaja Kalevi 
Published: May 2005

AbstractSeventeenN‐substituted 3,4‐dihydro‐2H‐1,3‐benzoxazines [N‐substituent = Et, Pri, But, CH2C6H5or CH(CH3)C6H5] were prepared and their structures studied in the light of13C chemical shifts. The γ effects caused by C(α)‐methyl or C(α)‐phenyl substitution at the heterocyclic ring carbons were found to be valuable structural parameters. By usingN‐tert‐butyl derivatives as models, and by dividing γtoteffects into their components, the rotamer populations due to the rotation around the NC(α) bond could be evaluated. The method also allows the configurational assignment of diastereomericN‐α‐methylbenzyl derivatives. The effect of the half‐chair structure on the13C NMR parameters is discussed.
Proton and carbon NMR spectra of 4‐substituted 1‐acetylnaphthalenes
Authors: Perumal S. , Vasuki G. , Wilson D. A. 
Published: May 2005

AbstractThe proton and carbon spectra of ten 4‐X‐l‐acetylnaphthalenes have been assigned. Shift correlations have been made with benzene substituent‐induced chemical shifts (SCS, Lynch plots) and with dual substituent parameters (DSP) in the manner successfully done for many series of 1,4‐disubstituted benzenes. The results obtained are compared with those for 4‐X‐acetophenones and 1‐X‐naphthalenes. The main conclusions are (i) the carbon para to the variable substituent X is more sensitive to change of substituent in the naphthalenes than in the benzenes, (ii) of the carbons ortho to the variable substituent X, that at C‐3 is more sensitive and that at C‐4a is less sensitive, to change of substituent in the naphthalenes than in the benzenes, (iii) the effect of the 4‐substituents on the shift of H‐8 in 1‐acetylnaphthalenes is due mainly to changes in the carbonyl dipole affecting the diamagnetic screening of the proton.
ESR, ENDOR and TRIPLE resonance studies on radical reactions of 1,4‐benzoquinone and 1,4‐hydroquinone in alkaline methanol and liquid ammonia
Authors: Joela H. , Kasa S. , Mäkelä R. , Salo E. , Hannonen K. 
Published: May 2005

AbstractThe relative signs and absolute values of the hyperfine coupling constants of different methoxy‐1,4‐benzoquinones were measured by ESR, ENDOR and TRIPLE resonance spectroscopy. Reactions of 1,4‐benzoquinone and 1,4‐hydroquinone with methanol took place in alkaline methanol, giving rise to methoxy‐substituted 1,4‐benzoquinones. The same substitution reaction occurred in a mixture of ammonia and methanol. The reactions depended on temperature and the alkali concentration. Coupling constants were assigned by the modified additivity relationship method. An extremely small line width of 0.014 G was measured in the ESR spectrum of deuterated 2,5‐dimethoxy‐1,4‐benzoquinone.
Stable conformations and energy barriers to rotation in perfluoro(4‐sec‐butylpyridine)
Authors: Sandall John P. B. , Sutcliffe Leslie H. 
Published: May 2005

AbstractAll‐valence‐electron MNDO–SCF–MO calculations were carried out on perfluoro(4‐sec‐butylpyridine) in order to calculate the stable conformations of the perfluoroalkyl group and the energy barrier to rotation of this group around the CalkylCaryl, bond. Both the AM1 and PM3 Hamiltonians were used. The results were compared with the value obtained from a variable‐temperature study of the 19F NMR spectrum of the compound. The PM3 method is shown to give a significant improvement compared with AM1.
Carbon‐13 chemical shift assignments of derivatives of benzoic acid
Authors: Wnuk Stanisław , Wyrzykiewicz Elżbieta , Kaczmarek Elżbieta , Kinastowski Stefan 
Published: May 2005

AbstractThe 13C NMR spectra of 23 di‐ and tri‐substituted derivatives of esters, thioesters and amides of benzoic acids have been calculated and fully assigned. The Ai empirical parameters of the (alkoxy)(dialkoxycar‐bonyl) methylamino, (alkoxy)(alkoxycar‐bonyl)(cyano)methylamino, (alkylamino) (dialkoxycarbonyl) methylamino and (alkylthio) (dialkoxycarbonyl) methylamino groups have been calculated for use in the prediction of the chemical shifts of substituted benzenes.
Conformational and dynamic investigation in solution of inosine and its molecular complex, inosiplex, by proton and carbon NMR spectroscopy
Authors: Rossi Claudio , Picchi Mariapia , Tiezzi Enzo , Corbini Gianfranco , Corti Piero 
Published: May 2005

AbstractThe conformational and dynamic properties of inosine and two other components of inosiplex (p‐acetamidobenzoic acid and dimethylaminoisopropanol) were analysed. For inosine, the most interesting molecule of the complex, the rotamer populations of all six allowed structures related to the N ⇌ S puckering and the 5′‐exocyclic conformation were calculated. Analysis of different NMR spectra and/or parameters, i.e. 2D‐NOE, saturation transfer, spinlattice relaxation rates and scalar coupling constants, suggests that a distribution of several inosine structures occurs in solution, with the inosine syn conformation predominating.
Cycloheptatrienyl radicals: An EPR study of substituent effects
Authors: MacCorquodale Finlay , Walton John C. 
Published: May 2005

AbstractCycloheptatrienyl radicals with donor and acceptor substituents were generated by hydrogen abstraction from the corresponding cycloheptatrienes and studied by EPR spectroscopy. The barrier to rotation about the C‐1CO bond in ethoxycarbonylcycloheptatrienyl radicals was found to be ca. 7.5 kcal mol−1 (31.4 kJ mol−1). The observed hyperfine splittings of the ring hydrogens were interpreted in terms of a model in which the substituent causes an energy separation ΔE between the frontier orbitals. Populations of the symmetric and antisymmetric orbitals were deduced, and ΔE values were estimated. A similar analysis was carried out from EPR data for substituted benzene radical anions. These energy separations show a linear correlation with Hammett constants. The p‐values from plots of this type for [n]annulene radicals decrease in magnitude as the size of the ring increases.
1H NMR structural analysis of a series of naphthalene‐hydroxymethyl‐and ‐mercaptomethyl‐carboxylic acids and derivatives
Authors: Tsatsakis A. M. , Dais Photis 
Published: May 2005

Abstract1H NMR chemical shifts allow the determination of some structural properties of a series of naphthalene‐hydroxymethyl‐ and ‐mercaptomethyl‐carboxylic acids and their derivatives used as potential pesticides.
13C NMR chemical shifts of 2,4,5,‐ tri‐substituted 2H‐pyridazin‐3‐ones
Authors: Liptaj T. , Konečny V. , Kovác Š 
Published: May 2005

AbstractThe 13C NMR spectra of a series of 2‐X‐4‐Y‐5‐Z‐substituted 2H‐pyridazin‐3‐ones were measured and assigned on the basis of results from one‐dimensional semi‐selective INEPT or one‐dimensional relayed coherence transfer (HICUUP) experiments.
15N, 13C and 1H NMR spectra of the 2:1 cobalt(III) complexes of some azo dyes
Authors: Lyčka Antonín , Jirman Josef , Cee Aleš 
Published: May 2005

AbstractThe 15N, 13C and 1H NMR spectra of 2:1 cobalt(III) complexes of azo dyes and their 15N isotopomers, derived from substituted 2‐hydroxyaniline azo coupling products with acetoacetanilide, were measured. It was found that, in contrast to precursors existing fully in their hydrazone forms, 2:1 cobalt(III) complexes exist in (E)‐azo configurations, cobalt being bound to oxygens which originate in hydroxy and amide groups and nitrogen from substituted anilines as starting material.
Stereochemistry of benzannelated 1,6‐diazabicyclo[4.2.1]octadienes and the conformation of substituents on the methylene bridge
Authors: Kleinpeter E. , Hartmann J. , Werner B. , Schroth W. 
Published: May 2005

AbstractThe stereochemistry of benzannelated 1,6‐diazabicyclo[4.2.1]octa‐3,7‐dienes (the conformation of the eight‐membered ring and of the variable substituents on the methylene bridge) was determined by means of NOE enhancements and stereospecific long‐range H,H coupling constants in the relevant NMR spectra.
Compounds with bridgehead nitrogen. 62—NMR spectra and stereochemistry of perhydropyrido[1,2‐c][1,3]thiazepines and related systems
Authors: Crabb Trevor A. , Fallah Asadollah 
Published: May 2005

AbstractPerhydropyrido[1,2‐c][1,3] thiazepine adopts (CDCl3 solution, 25°C) an equilibrium containing > 98% trans‐fused conformer, in contrast to perhydropyrido[1,2‐c][1,3]oxazepine, which adopts a ca. 74% trans‐fused ⇌ 26% O‐inside‐cis‐fused conformational equilibrium. The cis‐(H‐5a, H‐8)‐8‐ethyl‐substituted derivatives of both systems show increased preference for the S/O inside cis conformations. The related 2‐tert‐butylperhydropyrido[1,2‐c][1,3]diazepine adopts predominantly the trans‐fused conformation.
Liquid‐ and solid‐state (CP‐MAS) 13C and 207Pb nuclear magnetic resonance study of two triorganolead methoxides and a stabilized triorganolead cation
Authors: Wrackmeyer Bernd , Horchler Klaus , Sebald Angelika , Merwin Lawrence H. 
Published: May 2005

AbstractLiquid‐ and solid‐state NMR data (13C, 207Pb) are reported for three organolead compounds, Me3PbOMe (1) and two comparable heterocycles, 5,5,4‐tricyclopentyl‐2,5‐dihydro‐1,2,2,3‐tetramethyl‐1,2,5‐oxoniaplumbaboratol (2) and (E)‐2‐dimethyl‐3‐diisopropyl(propinyl)borata‐4‐methyl‐2‐pentene (3); 2 contains a bridging methoxy group, and a triorganolead cation is stabilized by a bridging alkynyl group in 3. Compound 1 is shown to be associated in solution and forms chains in the solid state with bridging methoxy groups. The 207Pb CP‐MAS NMR spectrum of 1 shows that there is a single lead site with near‐axial symmetry. Two‐dimensional heteronuclear 13C/1H shift correlations were used to obtain the relative signs of numerous J(207Pb13C) and J(207Pb1H) coupling constants. In the case of 2 and 3 the 1J(207Pb13CMe) coupling constants have a negative sign. This indicates an extremely distorted tetrahedral surrounding of the lead atom. The isotropic 207Pb chemical shifts of 2 and 3 are almost identical in the solid state and in solution. Therefore, the structures in the solid state are fully retained in solution. Quantitative analysis of the spinning side‐band pattern of the 207Pb CP‐MAS spectra gave similar chemical shift anisotropies, Δσ(207Pb‐1133) ppm (2) and ‐1223 ppm (3), and also similar tensorial components of σ(207Pb), indicating that the basic structures of the two heterocyclic systems are comparable except for the bridging unit.
Rotational isomerism in 5‐amino‐6‐(N‐methylformamido)‐as‐triazin‐3(2H)‐one
Authors: Riand Jacques , Tanguy Michel , Chenon Marie‐Thérèse , Tzeng Cherng‐Chyi , Panzica Raymond P. 
Published: May 2005

AbstractA 1H dynamic NMR study of the hindered rotation in 5‐amino‐6‐(N‐methylformamido)‐as‐triazin‐3(2H)‐one was conducted. Signals for two rotamers were observed and their proton chemical shifts were assigned. It was found that the rotamer in which the as‐triazine ring is cis to the formyl hydrogen predominates. The free energies of activation for hindered rotations about the N CHO and C NH2 bonds were determined by 1H NMR line‐shape analysis.
Sign and magnitude of the phosphorus–phosphorus coupling constant in the [cyclopentadienyltris(trimethylphosphine)iron]+ cation of [(η5‐C5H5)(Me3P)3Fe]BF4and the 13C/12C isotope effect on the 31P chemical shift
Authors: Buchner Wolfgang , Ries Wolfgang , Malisch Wolfgang 
Published: May 2005

AbstractThe 13C NMR methyl group multiplet of the [cyclopentadienyltris(trimethylphosphine)iron]+ cation was simulated to obtain the sign and magnitude of the phosphorus‐phosphorus coupling constant and the 13C/12C isotope effect on the 31P chemical shift.
77Se and 15N NMR investigation of some cycloalkeno‐1,2,3‐selenadiazole derivatives
Authors: Duddeck Helmut , Wagner Petra , Müller Dieter , Jászberényi Joseph Csaba 
Published: May 2005

AbstractThe 13C, 15N and 77Se NMR data (chemical shifts and coupling constants) of some cycloakeno‐1,2,3‐selenadiazoles are presented. Extremely large 77Se chemical shifts are found. 15N, 77Se coupling constants, obtained at natural abundance, are reported for the first time. Strong signal shifts due to different sizes of the cycloakeno rings can be qualitatively rationalized in terms of electron transfer between the nitrogen and selenium atoms. A positive γ‐syn effect of the methyl group on N‐3 is found in 4‐methyl‐4,5,6,7‐tetrahydrobenzo‐1,2,3‐selenadiazole.
13C and 15N NMR study of derivatives of N‐unsubstituted pyrrolidines
Authors: Barbry Didier , Hasiak Bruno , Couturier Daniel 
Published: May 2005

Abstract13C and 15N NMR data for twelve N‐unsubstituted pyrrolidines are reported and cis and trans stereomers are assigned for 2,3‐, 2,4‐ and 2,5‐disubstituted compounds.
13C NMR spin–lattice relaxation mechanisms of carbocations in superacids
Authors: Kelly David P. , Leslie D. Ralph 
Published: May 2005

AbstractThe contributions to the 13C NMR spin–lattice relaxation rates of both protonated and non‐protonated carbons of a range of carbocations in superacids were determined from the analysis of T1 values measured over a range of temperatures and at different field strengths. From the data for 1‐adamantyl, 2‐methyl‐2‐norbornyl, 3‐methyl‐3‐nortricyclyl, 2‐phenyl‐2‐norbornyl, cumyl (1‐methyl‐1‐phenylethyl) and methylphenylcyclopropylcarbinyl (1‐cyclopropyl‐1‐phenylethyl) cations, dipole–dipole interactions (both intra‐ and inter‐molecular) were found to be entirely responsible for the relaxation of protonated carbons. However, for the cationic carbons, chemical shift anisotropy contributes significantly to their relaxation at low field strengths (2.3 T) and predominantly at high field strengths (5.8 T). The shielding anisotropies (Δσ) of the cationic carbons were determined as 410–540 ppm, which are amongst the largest reported for any carbon atoms.
Substituent effects in the 13C NMR spectra of 17α‐ethinyl‐19‐nortestosterone derivatives
Authors: Hammann Peter E. , Wöbbecke Elke , Hoppen Hans‐Otto 
Published: May 2005

AbstractThe 13C NMR spectra of eight norethisterone derivatives are presented. Substituent chemical shifts for the methyl group at C‐18, the methylene group at C‐11 and the Δ15 double bond are evaluated and discussed.
13C NMR spectra of (E)‐2‐pyridinecarbaldehyde pyridin‐2′‐ylhydrazone and eight analogues
Authors: Casey Allan T. , Traverso Ivan P. 
Published: May 2005

AbstractThe total assignment of the 13C NMR spectra of (E)‐2‐pyridinecarbaldehyde pyridin‐2′‐ylhydrazone and eight analogues is reported. The assignment of the spectra was achieved by comparison with data from the hydrazone precursors and other similar compounds.
Characterization of cyclonerodiol isolated from corn infested by fusarium moniliforme sheld.: One‐ and two‐dimensional 1H and 13C NMR study
Authors: Laurent D. , Goasdoue N. , Kohler F. , Pellegrin F. , Platzer N. 
Published: May 2005

AbstractA metabolite extracted from maize culture was identified as cyclonerodiol. Its 1H and 13C NMR spectra have been fully analysed, and some literature assignments have been reversed.
31P and 13C NMR studies on the phase structures of the binary barium ethyl octyl phosphate–water system
Authors: Yoshida Tadayoshi , Miyagai Kiyotaka , Taga Keijiro , Okabayashi Hirofumi , Matsushita Kazuhiro 
Published: May 2005

Abstract31P nuclear magnetic resonance (NMR) studies of the four phases (I, II, II′ and III) in the barium ethyl octyl phosphate‐water system were carried out. The concentration dependence of the 31P chemical shift, half‐height width and line shape provided information on the phase structures. For phase I the critical micelle concentration (CMC) is found at 1.2 wt.%, and above this concentration there is a monomer ⇌ micelle equilibrium. Phase II has a monomer ⇌ micelle equilibrium system, similar to phase I. Phase II′ is an aggregate system and is structurally organized. The structure of phase III is more organized than that of phase II′ and depends strongly on concentration. The 3J(POCC) values were also used to establish the restricted state of the POCC single bond in the phases.
19F NMR study of fluoro‐substituted tetracyclo[6.3.0.02,4.03,7]undec‐5‐enes
Authors: Osselton E. M. , Erkelens C. , Krijnen E. S. , Lempers E. L. M. , Cornelisse J. 
Published: May 2005

Abstract19F and 1H NMR data are reported for fluoro‐substituted tetracyclo[6.3.0.02,4.03,7]undec‐5‐enes, which are products of the meta photocycloaddition reaction of fluorobenzenes to cyclopentene. Hetero‐ and homo‐nuclear decoupling techniques were used to identify the adducts.
HMQC‐NOESY: Application to a polynuclear aromatic at natural abundance
Authors: Ronald  , Crouch C. , Andrews C. Webster , Martin Gary E. , Luo Jiann‐Kuan , Castle Raymond N. 
Published: May 2005

AbstractOrientation of proton spin systems relative to one another in polynuclear aromatics through the use of 1H homo‐nuclear nuclear Overhauser effects (NOE) detected by heteronuclear multiple quantum correlation (HMQC‐NOESY) at natural abundance is reported. The experiment was explored as a potential alternative for problems in which a solution cannot be obtained by more conventional methods. Optimization of the HMQC‐NOESY experiment is discussed.
13C NMR spectra of some substituted furo[3,2‐b] pyrroles
Authors: Dandárová Miloslava , Krutošíková Alžbeta , Aalföldi Juraj 
Published: May 2005

Abstract13C chemical shifts for 16 derivatives of furo[3,2‐b] pyrrole substituted at positions 2, 4 and 5 are reported. The J(CH) values were determined for some derivatives. Heterocorrelated 2D 1H‐13C NMR spectra, selective heteronuclear decoupling and selective INEPT experiments were used for signal assignment.
Analysis of the 1H and 13C NMR spectra of the novel macrolide antibiotic roxithromycin. Structure and conformation in solution
Authors: Gharbi‐Benarous Josyane , Delaforge Marcel , Artaud Isabelle , Girault Jean‐Pierre 
Published: May 2005

AbstractA complete assignment of the 1H and 13C NMR spectra of roxithromycin in deuteriochloroform, methanol‐d4 and D2O was made using different two‐dimensional (2D) chemical shift correlation methods. The coupling constants observed by 1H NMR and the NOEs show that the predominant conformation of roxithromycin in CDCl3 solution is very similar to that in the crystalline state. However, variable‐temperature and variable‐solvent NMR experiments show that the major conformation of roxithromycin presents a conformational flexibility in the C‐2–C‐8 region and, particularly, in the C‐4–C‐5 bond of the molecule. The NOE data indicate that the 9‐[O‐(2,5‐dioxahexyl)oxime] chain is directed towards the 6‐OH, certainly involving an intramolecular hydrogen bond. This results in a globular structure for roxithromycin with less freedom for the macrolactone ring and the sugar units.
A multinuclear magnetic resonance study of protonation in imidazo[1,2‐a]pyrazine
Authors: Sanderson P. N. , Farrant R. D. , Lindon J. C. , Barraclough P. 
Published: May 2005

Abstract1H and 13C NMR spectra are reported and assigned for imidazo[1,2‐a] pyrazine and for N‐1‐methyl‐ and N‐7‐methyl‐imidazo[1,2‐a] pyrazinium iodides. The effect of protonation on the chemical shifts of the parent molecule is demonstrated, and through the use of 13C and 15N NMR spectra the site of protonation is deduced to be at N‐1, in contrast to 2‐aryl substituted compounds synthesised as potential cardiotonic agents where protonation occurs at N‐7.