bluuebunny/crossref_metadata_2025_split huggingface dataset:
ESR studies on carboxylic esters. Part 13—electron spin resonance spectroscopy and molecular orbital calculations on the radical anions of 2‐oxo‐carbothioate and 2‐oxo‐carbodithioate esters
Authors: Gassmann J. , Günther H. , Osternack K. , Sawluk A. , Thimm K. , Voss J. 
Published: May 2005

AbstractRadical anions of alkyl α‐oxocarbothioates and α‐oxocarbodithioates are generated by in situ electroreduction. Their spin density distribution and configuration are discussed in terms of the ESR spectra and semi‐empirical (McLachlan‐type and AM1) MO calculations.
13C NMR of 4,5‐epoxy‐3‐substituted decalin and analogous Δ4‐octalin derivatives: Epoxide‐ and methyl‐induced shifts
Authors: Pohlit Adrian Martin , Ferraz Helena Maria Carvalho 
Published: May 2005

AbstractFully assigned 13C NMR chemical shifts for 4,5‐epoxy‐3‐keto‐, ‐3‐hydroxy‐, and ‐3‐acetoxydecalins and ‐10‐methyldecalins, Δ4‐octalins and 10‐methyl‐Δ4‐octalins are reported together with epoxide‐ and methyl‐induced shifts. The 4,5α‐ and 4,5β‐epoxydecalins present epoxide γ shielding in the A ring consistent in general with the syn‐axial hydrogen rule. The 4,5α‐ and 4,5β‐epoxy‐10‐methyldecalins present only slightly different shielding effects at γ‐carbons C‐1, C‐2, C‐7, C‐9 and C‐11. Methyl‐induced shifts in 4,5α‐ and 4,5β‐epoxy‐10‐methyldecalins are similar at all carbons to those for trans‐ and cis‐decalins (low temperature in the case of the latter), respectively, suggesting the predominance of the transoid and cisoid A ring conformations, respectively, in these epoxides. The methyl‐induced shifts in the A ring of octalin analogues are intermediate between those of the two epoxide configurational isomers. Epoxide γ‐anti deshielding and γ‐syn shielding (analogous to those in 5‐hydroxydecalins) are evident when comparison is made with 13C shifts from analogous decalins, in contrast to the result when these effects are evaluated with data for Δ4‐octalin analogues.
Detailed characterization by, two‐dimensional NMR of two unusual bicyclo [2.2.2]octenedione derivatives produced by the reaction of perezone with thiourea
Authors: Reynolds William F. , Yu Margaret , Ortiz Benjamin , Rodriguez Angel , Yuste Francisco , Walls Fernando , Enriquez Raul G. , Gnecco Dino 
Published: May 2005

AbstractA combination of NMR experiments, including 13C and 15N DEPT, COSY, NOESY, HMQC and HMBC experiments, was used to assign the structures and stereochemistries of two isomeric bicyclo[2.2.2]octenedione derivatives produced by the reaction of perezone with thiourea, followed by treatment with silica gel. A possible mechanism of the reaction is suggested.
Application of 19F NMR spectroscopy to the study of equilibrium dynamics of uranyl(2+)‐fluoride complexes
Authors: Szabó ZoltáN , Glaser Julius 
Published: May 2005

AbstractOne‐ and two‐dimensional magnetization‐transfer 19F NMR methods were applied in a quantitative study of the fluoride exchange for uranyl(2+)‐fluoride complexes in aqueous solution. The applicability of these techniques and the classical lineshape analysis is discussed, and the quality of the results (rate constants and relaxation rates) obtained by the three methods is compared.
13C NMR studies of some dialkyl α‐anilinobenzylphosphonates and dialkyl α‐anilino‐(2‐hydroxybenzyl)phosphonates
Authors: Ćurić M. , Tušek‐Božić Lj. , Vikic‐Topić D. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of dialkyl α‐anilinobenzylphosphonates and dialkyl α‐anilino‐(2‐hydroxybenzyl)phosphonates were measured. The assignment of the spectra was performed using a combination of 31P‐13C and 13C‐1H coupling constants and substituent‐induced chemical shifts. Long‐range phosphorus‐carbon couplings up to five bonds were observed.
2D NMR structure elucidation of proanthocyanidins: The special case of the catechin‐(4α‐8)‐catechin‐(4α‐8)‐catechin trimer
Authors: Balas Laurence , Vercauteren Joseph , Laguerre Michel 
Published: May 2005

AbstractA complete and unambiguous assignment of the 1H and 13C NMR spectra of peracetylated catechin‐(4α‐8)‐catechin‐(4α‐8)‐catechin procyandin trimer was accomplished by reverse two‐dimensional chemical shift correlation methods. An HMBC spectrum showed, for the first time, evidence of the sites of condensation between the interflavan units of a trimer. The 2,3‐trans stereochemistry of the C‐ and F‐rings are easily deduced from measurement of 3J coupling constants. The multiplicity analysis of the protons of the i‐ring in the terminal unit does not lead to such an assignment. A ROESY experiment is needed to confirm the 2,3‐trans relationship. Molecular mechanics calculations explain the unexpected coupling constants of these protons.
Conformational analysis of benzoannulated nine‐membered rings. Part 4—7,8‐dihydro‐6H‐dibenzo[f,h][1,5]dioxonin and its derivatives
Authors: Rys Barbara , Duddeck Helmut 
Published: May 2005

AbstractTemperature‐dependent 1H and 13C NMR spectra of the title compounds are presented. The coalescence effects in the spectra are discussed and assigned to the racemization of the C2 symmetry conformation of the nine‐membered ring. The barrier of this process is ca. 64 kJ mol−1. A spirocyclohexane derivative revealed a second conformational process namely inversion of the six‐membered ring.
Gradient‐enhanced SELINCOR for selective excitation in a 13C‐resolved COSY experiment
Authors: Fäcke Thomas , Berger Stefan 
Published: May 2005

AbstractThe performance of the SELINCOR sequence is greatly enhanced by using pulsed field gradients. It is shown that with this sequence, a 13C‐resolved COSY can be performed on a selected proton of an attached carbon atom. This experiment enables one to detect and evaluate COSY cross peaks in otherwise overcrowded regions.
35Cl/37Cl one‐bond isotope effects on 13C chemical shifts in a series of para‐substituted chlorobenzenes
Authors: Morales‐Ríos Martha S. , García‐Martínez Cirilo , Joseph‐Nathan Pedro , Zepeda L. Gerardo 
Published: May 2005

AbstractOne‐bond isotope shifts of 35Cl/37Cl natural abundance chlorine isotopomers were measured in the 75.4 MHz 13C NMR spectra of a series of para‐substituted chlorobenzenes. The high‐field isotope shift effect 1Δ13C(37Cl) was established from the relationship between the chlorine isotopomeric ratio and the carbon peak intensities. It was found that the 1Δ13C(37Cl) values are in the range of −4.0 to −5.2 ppb. The isotope shifts tend to decrease as the electron‐attracting character of the substituent increases, providing a linear correlation between the isotope shift and the chemical shift of the chlorine‐bearing carbon.
NMR investigation of the intramolecular distribution of deuterium in natural triacylglycerols
Authors: Lai Adolfo , Casu Mariano , Saba Giuseppe , Corongiu F. P. , Dessì M. A. 
Published: May 2005

AbstractThe 1H and 2H NMR spectra of a number of edible oils were investigated. The average numbers of hydrogens and deuteriums for the olefinic, methylene and methyl sites in mixtures of triacylglycerols were determined, and some parameters describing the different fractionation of deuterium in the various sites were obtained. These results are discussed in connection with the biosynthesis steps involved in the elongation and desaturation processes of the fatty acid components.
Concerted application of a shift reagent and 2D NOESY to the structure determination of new natural products from the tropical brown alga Dictyopteris delicatula
Authors: König Gabriele M. , Wright Anthony D. 
Published: May 2005

AbstractFrom the marine brown alga Dictyopteris delicatula Lamaouroux, two new (1, 3) and two previously reported sesquiterpenes (2, 4) were isolated and characterized. Compound 1 was identified as 4β,5α‐dihydroxycubenol and 2 was found to be a non‐racemic mixture of (±)‐torreyol. Compound 3 was characterized as cubenol‐3‐one and 4 was identified as cubenol. For the assignment of the complete relative stereochemistry of compounds 1 and 2, it was necessary to employ extensive 2D NMR methodologies in combination with the lanthanide shift reagent europium(III) tris(1,1,1,2,2,3,3)‐heptafluoro‐7,7‐dimethyl‐d6‐octane‐4,6‐dione‐d3 [Eu(fod)3]. Anomalous proton shielding effects which occurred on addition of Eu(fod)3 to compound 1 suggested that classical lanthanide‐induced shift (LIS) analysis for predicting proton chemical shifts was not applicable. Application of 2D NOESY measurements to NMR samples of 1 and 2 containing Eu(fod)3 clearly demonstrated an alternative to classical methods for interpreting lanthanide‐induced shifts. The enhanced value of shift reagnents of this type as an aid to structure determination and as for assignment purposes is demonstrated.
Indirect detection of selenium‐77 in nuclear magnetic resonance spectra of organoselenium compounds
Authors: Schroeder T. Benjamin , Job Constantin , Brown Michael F. , Glass Richard S. 
Published: May 2005

Abstract77Se was measured by inverse proton detection using multiple‐quantum 1H‐{77Se} correlation spectroscopy. One‐and two‐dimensional heteronuclear multiple quantum coherence (HMQC) experiments are reported for selenophene, benzeneselenol, dimethyl selenide, dimethyl diselenide, and D,L‐selenomethionine with a range of 77Se1H coupling constants from 9.5 to 54.2 Hz. In these compounds having protons with different 77Se1H coupling constants the different correlations can be selectively enhanced by varying the mixing time. The enhancement for indirect versus direct 77Se detection was estimated for dimethyl selenide yielding a value close to the theoretical enhancement.
Two‐dimensional NMR of sesquiterpenes. 8—complete assignment of 1H and 13C NMR spectra of seven sequiterpene alcohols from Neocallitropsis pancheri
Authors: Raharivelomanana Phila , Bianchini Jean‐Pierre , Cambon Aimé , Azzaro Marcel , Faure Robert 
Published: May 2005

AbstractThe complete assignment of the proton and carbon NMR spectra for seven sequiterpene alcohols isolated from the heartwood oil of Neocallitropsis pancheri, namely, α, β‐ and γ‐eudesmol, carissone, guaiol, bulnesol and elemol, was achieved using the concerted application of one‐and two‐dimensional NMR techniques including DEPT, COSY, HETCOR and HMBC spectroscopy. The parameters previously reported in the literature were found to be often wrong or incomplete.
31P NMR spectroscopic investigation of exchange processes in two bifunctional aminophosphonates
Authors: Boetzel R. , Failla S. , Finocchiaro P. , Hägele G. 
Published: May 2005

AbstractVariable‐temperature 31P NMR spectroscopy was used to extract Arrhenius and Eyring parameters of the hindered rotation about amide bonds in an acylated aminophosphonate. The results permit the differentiation between stepwise or concerted rotation.
Electron‐nuclear relaxation time T1e for intramolecular distance evaluation
Authors: Cinget Francis , Fries Pascal H. , Greilich Ulrike , Vottéro Philippe J. A. 
Published: May 2005

AbstractCarbohydrate molecules labelled by TEMPOL nitroxide radicals in dilute deuteriochloroform solutions are considered. The distances between 13C nuclei and the nitroxide free electron are related to the measured contributions to the 13C longitudinal relaxation rates which stem from the dipolar coupling with the electron spin. It is shown that a correct interpretation of these electron‐nuclear relaxation times rests on an accurate knowledge of the effective viscosity experienced by the labelled solute. This microviscosity can be roughly estimated from a simple hydrodynamic model which takes the difference in sizes of the solute and solvent molecules into account. A more accurate experimental determination is obtained by measuring the electron‐nuclear relaxation times of the cyanide 13C spin on a rigid cyano‐TEMPOL radical used as a microviscosity probe. Various models of rotational diffusion are considered. The anisotropy of the rotational motion of the labelled sugar and a possible contraction‐expansion of the electron‐13C distances due to dynamic conformational changes are examined, and their effects on the relaxation times are calculated. The delocalization of the paramagnetic free electron is taken into account, and a theoretical model for calculating its influence on the relaxation is presented. To our knowledge, this is the first study showing the importance of the electronic spin delocalization which reduces the relaxation times by a factor of 2 for the cyano‐TEMPOL. Using a theory which incorporates the correct microviscosity, rotational anisotropy and free electron delocalization, the electron‐13C distances of the labelled sugar, which give theoretical relaxation times in agreement with the experimental data, are found to be nearly equal to the values determined by X‐ray studies. The solute appears to have a stretched rigid shape in chloroform over a large temperature range. Electron‐nuclear relaxation studies allow the evaluation of intramolecular interspin distances up to 10–15 Å in length with an accuracy of about 5%.
Eupomatenoids from Caryodaphnosis tonkinensis and their complete NMR assignment
Authors: Himmelreich Uwe , Ripperger Helmut , Adam Günter , Anh Nguyen Hoang , van Sung Tran 
Published: May 2005

AbstractEupomatenoids 3–6 and 13 were isolated from Caryodaphnosis tonkinensis and their 1H and 13C NMR spectra were assigned using 1D and 2D NMR techniques. Different assignment strategies are presented for the 1H and 13C chemical shifts. 1D NOE difference spectra, 1D APT, HMQC, HMBC, H,H‐COSY‐90 and delayed H,H‐COSY‐45 were used.
Vitamin B‐6 model reactions. Part VI‐a Hammett relationship for the magnitude of pseudoallylic proton‐proton spin coupling constants in substituted azomethines
Authors: Fischer James R. , Abbott Edwin H. 
Published: May 2005

AbstractFour‐bond proton‐proton spin coupling constants were measured between the azomethine proton and the glycine CH protons of some coordinated glycine Schiff bases where the parent aldehyde is aromatic. Such systems are models for vitamin B6 enzyme substrate complexes. It is demonstrated that the coupling constants are not only related to the dihedral angles between coupled systems but they are also linearly related to the Hammett σ value of the substituents on the aromatic ring. A method is suggested for the calculation of dihedral angles between proton‐carbon bonds in these pseudoallylic systems.
Complete 1H and 13C NMR assignment of ent‐3β,16α‐atisanediol, a cytotoxic diterpene isolated from the sponge Spirastrella cunctatrix
Authors: Cafieri Francesco , Fattorusso Ernesto , Mahajnah Yosef , Mangoni Alfonso 
Published: May 2005

AbstractFull assignment of the 1H and 13C NMR spectra of ent‐atisane‐3β,16α‐diol, a cytotoxic diterpene isolated from the Caribbean sponge Spirastrella cunctatrix, was achieved by extensive use of two‐dimensional NMR spectroscopy and spectral simulation. This is the first complete NMR characterization af an atisane terpene.
Substituent effects on 13C NMR parameters of chlorinated diphenyl ethers. A multiple linear regression analysis
Authors: Nevalainen Tapio , Kolehmainen Erkki , Vilén Esa 
Published: May 2005

Abstract13C NMR chemical shifts and nJ(C,H) coupling constants of polychlorinated diphenyl ethers (PCDEs) were measured and analysed. The chlorine substituent effects on the chemical shifts and the coupling constants were determined by a multiple linear regression analysis. The 13C NMR chemical shifts depend on the conformational preferences in PCDEs. In addition to single substituent effects, corrective terms reflecting the conformational state of the molecule and the mutual steric interactions of two chlorine atoms had to be taken into account for the reliable prediction of the 13C chemical shifts. In contrast to chemical shifts, conformational effects play a minor role in the substituent effects of the nJ(C,H) coupling constants. Coupling constants are approximately additive in terms of ‘simple sum rules’.
EPR study of β‐methylene proton magnetic inequivalence in monomeric addition radicals derived from mono‐ and 1,1′‐disubstituted ethylenes with chiral and non‐chiral substituents
Authors: Smith Peter , Donovan William H. , Mader Charles E. , Dominguez Luis M. , Koscielniak Walter T. 
Published: May 2005

AbstractUsing rapid‐mixing, continuous‐flow TiCl3‐based techniques at 25°C monomeric addition radicals of general formula ·CX(Y)CH2C*HR1R2, where R1 and R2 are different groups, neither being H, so that C* is a chiral center, were characterized by electron paramagnetic resonance. These species were generated by adding ·CH(CH3)OH, CH(CH3)OCH2CH3,.CH(CH3)OC(O)H,.CH(CH3)OC(O)CH3 and radicals in turn to each of the monomers, of general structure CX(Y)CH2, acrylonitrile, acrylic acid, tert‐butyl acrylate, butyl acrylate, methacrylonitrile, methacrylic acid, itaconic acid and but‐3‐ene‐1,2,3‐tricarboxylic acid. Similar reactions of carbon‐centered radicals with vinyl fluoride and 1,1‐difluoroethylene did not yield detectable levels of the expected addition radicals. In every addition radical observed, the splittings of the β‐CH2 protons were found to be unequal and the size of this inequivalence varied qualitatively with the bulkiness of X, Y, R1 and R2. Similar measurements on monomeric addition radicals of general formula.CX(Y)CH2Z, where Z is achiral, generated in turn from the same monomers by adding.OH,.NH2 and, showed no evidence for the β‐CH2 proton splittings to be unequal. These results demonstrate the importance of an awareness of chirality effects in interpreting EPR spectra of monomeric and polymeric addition radicals of mono‐ and 1,1′‐disubstituted ethylenes.
Electron paramagnetic resonance spectra of chromium(III) in titanium dioxide polymorphs: Exact analysis and simulation by the isotimic method
Authors: Beltran L. Virgilio , Tovany Luis Gonzalez , Mile Brynmor , Rowlands Christopher C. 
Published: May 2005

AbstractThe isotimic method allows a full analysis and accurate simulation of the experimental EPR spectrum of Cr(III) ions in axial field sites in the anatase polymorph of TiO2. The precise estimates of the magnetic and crystalline field parameters obtained from an optimum fit of experimental and simulated spectra are geff = 1.9734 ± 0.0005, D = 40.6 ± 0.2 mT and a Lorentzian linewidth of Γ = 0.1 mT.
Primary and secondary deuterium‐induced isotope effects for 13C NMR parameters of benzaldehyde
Authors: Vujanić P. , Gacs‐Baitz E. , Meić Z. , Šuste T. , Smrečki V. 
Published: May 2005

AbstractDeuterium‐induced isotope effects on 13C chemical shifts and 1J(13C‐α, 1H) coupling constants in benzaldehyde were measured. Over 30 different effects on 13C chemical shifts were revealed. The effects through one (1Δ) and two bonds (2Δ) have mean values of 282.1 ± 9.6 and 109.5 ± 3.1 ppb, respectively, which is consistent with previously observed trends. Exceptions are [α‐2H] benzaldehyde and [o‐2H] benzaldehyde, where 2Δ values at the quaternary carbon C‐1 of only 72.6 and 69.6 ppb, respectively, were determined. While 3Δ at the C‐2,6 site in [p‐2H] benzaldehyde is absent, three different 3A effects in [o‐2H] benzaldehyde were observed. The longest range effect is 5Δ = −1.9 ppb, observed in [p‐2H] benzaldehyde. The role of the position and the number of incorporated deuterium atoms with respect to the range, magnitude and sign of these effects is discussed. Some of the observed effects are rationalized through interactions with lone‐pair electrons at the oxygen atom. A number of carbon‐deuterium coupling constants, nJ(13C,2H), through one, two and three bonds were measured. A single primary deuterium isotope effect on 1J(13C‐α,1H) in [α‐2H] benzaldehyde was determined, whereas no secondary effect through three or more bonds on the same coupling constant was observed.
Multinuclear magnetic resonance study of aluminum(III)‐isothiocyanate complexes in water‐acetone mixtures
Authors: Fratiello A. , Kubo‐Anderson V. , Bolanos E. , Chavez O. , Ortega J. V. , Perrigan R. D. , Reyes A. , Stoll S. M. 
Published: May 2005

AbstractA multinuclear magnetic resonance (NMR) study of the complexes of aluminum(III) with isothiocyanate ion in water‐acetone mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate resonance signals are observed for coordinated and bulk H2O (1H) and NCS− (13C, 15N), and Al3+ (27Al) in each complex. The 1H NMR spectra reveal six sets of signals for the complexes, [Al(H2O)6]3+ through [Al(H2O)(NCS)5]2−, including isomers for three of the species. Signal area measurements show a decrease in the Al3+ hydration number with increasing NCS− concentration, as this anion replaces water in the solvation shell. In the 27Al NMR spectra of these systems, signals for seven complexes, [Al(H2O)6]3+ through [Al(NCS)6]3−, are observed, with chemical shifts increasing by about 6 ppm with each additional NCS−. Although broadened somewhat by the Al(III) quadrupole, the 13C and 15N NMR spectra also reveal coordinated NCS− signals for these complexes, including 27AlN13CS J‐coupling in [Al(NCS)6]3−. Area evaluations of the 15N NMR signals provide an excellent complement to the 1H hydration number data. These NMR results demonstrate that a multinuclear approach to the study of solution complexes can provide detailed structural information about the species being formed.
2‐(p‐dimethylaminophenyl)indan‐1,3‐dione‐2‐yl radical: ENDOR and ESR studies and MNDO calculation
Authors: Motyakin M. V. , Pisarenko L. M. , Schuler P. , Stegmann H. B. 
Published: May 2005

AbstractENDOR and ESR spectra of the 2‐(p‐Dimethylaminophenyl)indan‐1,3‐dione‐2‐yl radical were measured in toluene and diethyl phthalate at 350 K. A solvent dependence of the coupling constants was observed. Using the MNDO method, the optimized structure of the radical and the spin population distribution were derived.
Nuclear quadrupole resonance and molecular orbital studies of charge distribution in H‐bonded complexes of 2‐chloro‐4‐nitrobenzoic acid
Authors: Habeeb M. M. , Awad M. K. 
Published: May 2005

AbstractThe charge distribution in hydrogen bridges of varying strengths in solid 2‐chloro‐4‐nitrobenzoic acid complexes was studied using the 35Cl nuclear quadrupole resonance technique (NQR). The dependence of 35Cl NQR frequencies on the proton affinities was analysed. Molecular orbital calculations using atom superposition and electron delocalization molecular orbital theory showed that the trends of changes in the charge density on the chlorine, nitrogen and oxygen atoms, and on the binding energy and the bond order of NH and OH groups are consistent with the NQR results. Also, the agreement between theoretical and experimental results showed that the 3,5‐dimethylpyridine complex represents the critical point at 50% proton transfer.
77Se and 13C NMR spectroscopy of some 1,2,3‐selenadiazoles
Authors: Duddeck Helmut , Hotopp Torsten 
Published: May 2005

Abstract77Se and 13C chemical shift of 19 1,2,3‐selenadiazoles are discussed in terms of substituent effects and conforma‐tional behaviour of the molecules. It is shown that the 77Se chemical shifts of such compounds are suitable tools for chiral discrimination in diastereomeric compounds.
13C NMR assignments of conforma‐tionally defined 6‐s‐trans‐retinoids
Authors: Vaezi M. F. , Brouillette W. J. , Muccio D. D. 
Published: May 2005

AbstractA new class of vitamin A analogs (retinoids) was synthesized containing a dimethylene bridge to maintain a 6‐s‐trans conformation of the terminal double bonds. The 1H and 13C NMR spectra were assigned for 15 new compounds, including E‐Z isomers (all‐E, 13Z, 9Z and 9Z,13Z) of retinoids containing an ethyl ester and car‐boxylic acid polar end groups, and also the (all‐E)‐isomer of the retinoids with an alcohol and aldehyde polar end‐groups and five C15 intermediates. The assignments were based on long‐range 1H13C heteronuclear 2D experiments.