bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic interactions implied by the non‐additivity of carbon‐13 substituent parameters in 2‐substituted cyclohexanones
Authors: Basso Ernani A. , Kaiser Carlos , Rittner Roberto , Lambert Joseph B.
Published: May 2005

The carbon‐13 chemical shifts were assigned for all ring positions in cyclohexanone and 4‐tert‐butylcyclohexanone with H, F, Cl, Br, I, MeO, MeS, MeSe, Me2N, Me or tert‐butyl in the 2‐position. The substituent‐induced shifts were calculated by difference from unsubstituted cyclohexanone or 4‐tert‐butylcyclohexanone. Both stereoisomers (cis and trans) were available for the 4‐tert‐butylcyclohexanones in all but one case. Comparison of the substituent‐induced shifts for the cis (equatorial 2‐substituent) and trans (axial 2‐substituent) isomers provides stereochemical insight into the interactions between the 2‐substituent and the carbonyl group that bring about non‐additivity of the substituent effects. In the 2‐equatorial isomer, the dipole–dipole interaction between the functional groups causes non‐additivities for the C‐2 carbon that depend largely on the electronegativity of the 2‐substituent. In the 2‐axial isomer, hyperconjugation or other orbital interactions between the groups cause non‐additivities for the C‐2 carbon that depend largely on the polarizability in addition to the electronegativity of the 2‐substituent.
183W NMR spectroscopy of W(VI) imidoaryl and imidoalkyl complexes using inverse detection based on non‐specific long‐range interactions
Authors: Macchioni Alceo , Pregosin Paul S. , Rüegger Heinz , van Koten Gerard , van der Schaaf Paul A. , Abbenhuis Rob A. T. M.
Published: May 2005

183W NMR spectra for a series of octahedral W(VI) imidophenyl, ‘WNPh’ and W(VI) imidoethyl, ‘WNEt,’ complexes were obtained using inverse detection based on non‐specific long‐range interactions. The metal couples to both the ortho and para protons of the NPh moiety (four and six bonds, respectively). The 183W shift is shown to be sensitive to the nature of the ligand and the coordination number. The effect of geometric isomerism on δ183W is shown to be several hundred ppm. Some δ14N and δ15N and 1J(183W,15N) data are reported. A number of new geometric isomers, involving the position of the NR ligand with respect to the remaining ligands, have been identified.
Conformational analysis. Part 20—conformational analysis of 4‐deoxy‐4‐fluoro‐D‐glucose and 6‐deoxy‐6‐fluoro‐D‐galactose in solution
Authors: Abraham Raymond J. , Chambers Eric J. , Thomas W. Anthony
Published: May 2005

The 1H and 19F NMR spectra of the α‐ and β‐pyranose anomers of 4‐deoxy‐4‐fluoro‐D‐glucose (4FG) and 6‐deoxy‐6‐fluoro‐D‐galactose (6FGA) in methanol‐d4, DMSO‐d6, acetone‐d6 and D2O solution are reported. Computer analysis of the ABMX spectra of the CHCH2F fragments gives accurate vicinal HH and HF coupling constants. An iterative computational analysis of the observed vicinal couplings in this fragment for 6FG, 6FGA and other molecules allows the determination of both the individual rotamer couplings and the rotamer populations. Consideration of the derived rotamer couplings strongly suggests that the correct assignment for the prochiral C‐6 methylene protons in 6FG is that with the 6S proton having the larger coupling to H‐5. This is the reverse of the assignment of these protons in D‐glucose. In contrast, the assignment of these protons in 6FGA follows that given previously for D‐galactose. The relative energies for the conformations about the C‐5C‐6 bond for 4FG, 6FG and 6FGA are given from the derived rotamer populations. For 6FGA the rotamer in which the fluorine is antiperiplanar to C‐4 is particularly favoured. For 4FG the rotamer with OH anti‐periplanar to the ring O is highly unfavoured, but the other two rotamers are of almost equal energy. Consideration of the effect of replacing hydroxyl by fluorine in these molecules indicates that any hydrogen bonding involving the C‐4 or C‐6 hydroxyls plays little part in determining the conformer energies of glucose or galactose in polar solutions.
Stereochemistry of 4‐amino‐(D3)‐trishomocubanes. NMR study of 3‐phenyl‐4‐amino‐(D3)‐trishomocubane
Authors: Oliver D. W. , Dekker T. G. , Wessels P. L.
Published: May 2005

Amino compounds of the highly symmetrical (D3)‐trishomocubane were recently shown to possess promising biological activities, i.e. antiviral and antiparkinson. This series was synthesized via a modified Ritter reaction. The unique hydrocarbon skeleton of these compounds has a D3 point group symmetry with a propeller shape. Several geometrical isomers are possible for the derivatives of (D3)‐trishomocubane. This paper reports the complete 1H and 13C NMR assignments and the configuration at C‐4 of one of the most promising compounds of the present series, i.e. 3‐phenyl‐4‐amino‐(D3)‐trishomocubane. The 13C NMR spectrum of this amine indicates the presence of only one geometrical isomer for the compound. NOE experiments on the fully assigned 1H NMR spectrum show that this isomer has the 3S4S/3R4R configuration, and not the 3S4R/3R4S configuration. These results indicate that the Ritter rearrangement proceeds stereospecifically and that it provides a facile method for the synthesis of (D3)‐trishomocuban‐4‐amines from tertiary alcohols of pentacyclo[5.4.0.02,6.03,10.05,9] undecan‐8‐ol.
NMR study of the inclusion complex formed between γ‐cyclodextrin and TmDOTP5−
Authors: Sherry A. Dean , Zarzycki Ryszard , Geraldes Carlos F. G. C.
Published: May 2005

The host–guest complex formed in aqueous solution between γ‐cyclodextrin (γ‐CD) and the macrocyclic paramagnetic shift reagent TmDOTP5− was examined by NMR spectroscopy. Paramagnetic lanthanide‐induced shifts (LIS) and spin‐lattice relaxation rate enhancements in the proton resonances of γ‐CD on binding of TmDOTP5− were used to define the position of the guest anion within the host cavity. A proportionality constant which relates pseudo‐contact shifts induced by TmDOTP5− to the geometrical position of each ligand nucleus (previously determined from a LIS study of the TmDOTP5− complex) was used to determine a fully bound LIS value for each γ‐CD proton. These values, in combination with experimental LIS data from TmDOTP5− titrations at constant γ‐CD concentration, were then used to obtain the association constant for the host‐guest complex (3.9–4.5 mol l−1). These constants were indicative of a weak host‐guest interaction and consistent with the location of the TmDOTP5− binding site reported by the LIS values well above the center of the γ‐CD cavity.
1H and 13C NMR of substituted dibenzo‐14‐crown‐4 ethers
Authors: Chen Zhihong , Sachleben Richard A.
Published: May 2005

Dibenzo‐14‐crown‐4 and eight substituted dibenzo‐14‐crown‐4‐ethers were studied by 1D and 2D 1H and 13C NMR and their chemical shifts are reported.
Isotope effects on the 13C chemical shift and carbon–proton coupling constant in dichloromethane
Authors: Sergeyev N. M. , Sergeyeva N. D. , Raynes W. T.
Published: May 2005

Carbon–proton and carbon–deuteron coupling constants were measured in the isotopomers CH2Cl2, CHDCl2 and CD2Cl2. The primary and secondary isotope effects on the carbon–proton coupling are −0.60 (±0.05) and −0.25 (±0.01) Hz, respectively. The deuterium‐induced 13C isotope shifts proved to be almost linearly dependent on the number of deuterium atoms, although there is a small but significant non‐additivity.
Conformational studies on phosphorus‐containing macrocycles
Authors: Boese R. , Boetzel R. , Hägele G.
Published: May 2005

H,H and P,H coupling constants and variable‐temperature 1H and 13C NMR spectra and 13C T1 values for some macrocyclic dithiophosphonic esters are presented to show that these compounds possess reduced flexibility in comparison with crown ethers. The NMR spectroscopic results are supported by an x‐ray structure which shows a highly strained ring system.
Solution and solid‐state structural chemistry of tungsten pyrazolylborate π‐allyl complexes: 2D 183W and 1H NOESY NMR studies
Authors: Pregosin Paul S. , Macchioni Alceo , Templeton Joseph L. , White Peter S. , Feng Shaoguang
Published: May 2005

2D1H NOESY and inverse detected 183W NMR measurements for the pseudo‐octahedral η3‐allyl complexes W(CO)2(Tp′)(η3‐CH2CHCDPh) (1) and W(CO)2(Tp′)(η3‐CH2CHCHCH3) (2), where Tp′ = hydridotris(3,5‐dimethylpyrazolyl)borate are reported. The observed solution structure for 1 differs from that found in the solid‐state via x‐ray diffraction (isomers can arise due to allyl rotation and/or coordination of either allyl face). Crystal data for 1: WC26H31BN6O3, space group P21/c, a = 9.775(1) Å, b = 17.360(2) Å, c = 16.144(5) Å, β = 102.26(2)°, V = 2677(1) Å3, Z = 4.
Total assignment of the 1H and 13C chemical shifts for a mixture of cis‐ and trans‐p‐hydroxycinnamoyl esters of taraxerol with the aid of high‐resolution, 13C‐detected, 13C1H shift correlation spectra
Authors: McLean Stewart , Reynolds William F. , Yang Ji‐Ping , Jacobs Helen , Jean‐Pierre Laurent L.
Published: May 2005

A mixture of two slowly interconverting isomeric compounds was isolated from Bernardia laurentii and identified as the trans‐ and cis‐p‐hydroxycinnamoyl esters of the triterpene taraxerol. Their 13C and 1H NMR spectra were totally assigned with the aid of concerted two‐dimensional NMR experiments. Not all assignments could be made using HMQC and HMBC owing to the limited 13C resolution and severe spectral crowding. However, the assignments could be made unambiguously by HETCOR and FLOCK experiments, relying on the superior 13C resolution of the 13C‐detected experiments. Comparison of 13C spectral assignments for a series of eight pentacyclic triterpenes with identical A and B ring structures but differences in C, D and/or E rings illustrates the risks and limitations of the use of model compounds for spectral assignments.
Data for the characterization of the geometrical isomers of β‐sulphinylenamines
Authors: Kozerski L. , Kawȩcki R. , Hansen P. E.
Published: May 2005

NOE experiments at low temperature were used to establish the structure of the E‐ and Z‐isomers of the enamine ButSOCHCHNHBut. The NOE experiments revealed large intermolecular NOE effects between E‐ and Z‐isomers indicating the formation of dimers of specific orientation. NH chemical shifts and their temperature dependence showed that the E‐ and Z‐ isomers behave differently. The NH chemical shifts of the former go to higher frequencies on lowering the temperature, whereas the opposite holds for the (Z)‐NH resonance. Similar trends are found on increasing the concentration. The orientation around the C1N bond can be probed by 3J(H1,NH) or by 1J(N,H). The 15N chemical shifts were also investigated in a series of β‐sulphinylenamines. They are mainly dominated by α‐ and β‐effects and show only a slight dependence on the E/Z isomerism, which seems to indicate a weak hydrogen bond in the Z‐isomer at high concentration. Pertinent NMR parameters are now available for a general structure determination of geometrical isomers of β‐sulphinylenamines.
Spin trapping of sterically unhindered phenoxyl radicals with nitrosobenzene and nitrosodurene
Authors: Omelka Ladislav , Kováčová Jana
Published: May 2005

Unhindered phenols were oxidized with PbO2 in the presence of nitrosobonzene and nitrosodurene. The phenoxyl radicals generated are trapped in their resonance form as ortho‐carbon‐centred radicals. Depending on the substitution of the spin trap, two types of aminoxyl radicals are formed. Stable diarylaminoxyls are the final products of the spin‐trapping reaction with nitrosodurene. The adducts of the ortho‐carbon‐centred phenoxyl radicals with nitrosobenzene are rapidly rearranged to the phenoxazine‐10‐oxyl radicals, the only radical products observed. Some exceptions to this rule are discussed. Radical products were characterized by their EPR parameters.
1H and 13C nuclear magnetic resonance studies of pyrazolo [c]‐ and pyrazolo [b]phenothiazines
Authors: Boyer G. , Galy J. P. , Faure R. , Barbe J.
Published: May 2005

The complete assignment of the 1H and 13C NMR spectra of eight Pyrazolo[b]‐ and pyrazolo[c]phenothiazines was performed using 1H detected one‐bond heteronuclear multiple quantum coherence (HMQC) and long‐range (two and three bonds) heteronuclear multiple quantum bond connectivity (HMBC) experiments. 1H and 13C NMR chemical shifts are also reported for some N‐arylindazoles
29Si and 13C NMR spectra of trimethylsilylated amino acids
Authors: Schraml Jan , Kvíčalová Magdalena , Schwarzová Iveta , Velíšek Jan
Published: May 2005

The 29Si and 13C NMR chemical shifts are reported for trimethylsilyl derivatives of 25 amino acids, the majority of which occur naturally as protein constituents of foodstuffs. The 29Si chemical shifts in trimethylsilyl esters of amino acids roughly correlate linearly with the pK values of the parent amino acid. No such simple correlations were found for the shifts in the fully trimethylsilylated amino acids. The 29Si chemical shifts of various functionalities encountered fall into distinct spectral regions, but the shifts of (CH3)3SiN or (CH3)3SiOOC groups alone are not sufficiently characteristic to identify the acid but their combination is in most cases.
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

Radical 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

Fully 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

A 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

One‐ 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

The 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

A 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

Temperature‐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

The 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

One‐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

The 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

From 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

77Se 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

The 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

Variable‐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

Carbohydrate 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

Eupomatenoids 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

Four‐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

Full 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

13C 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

Using 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

The 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

Deuterium‐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

A 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

ENDOR 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

The 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

77Se 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

A 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.
Electron paramagnetic resonance investigation of the complexes of grignard reagents with 9,10‐phenanthrenesemiquinonate
Authors: Pan Kai , Cheng Kung‐Lung , Ho Tong‐Ing
Published: May 2005

The substituent effect on the proton hyperfine splitting constants (hfsc) of the charge‐transfer complexes of Grignard reagents (RMgBr, R = CH3, C2H5, CH3CHCH) with seven 3‐substituted 9,10‐phenanthroquinones is reported. A back‐donation bonding interaction between phenanthrenesemiquinonate anion radical π* and the magnesium p orbital is revealed by the hfsc analysis.
Ring a conformation in steroids. 3—Cyclosteroids and cyclopropanosteroids
Authors: Marat Kirk , Templeton J. F. , Ling Yangzhi , Lin Weiyang , Gupta R. K.
Published: May 2005

Proton and carbon NMR data are provided for 21 ring A and ring B cyclosteroids and cyclopropano (or methylene) steroids. Shift assignments were made using standard 2D NMR techniques, while ring A proton subspectra were extracted with a 1D TOCSY experiment. Coupling constants were obtained from iterative spin system simulation of these sub‐spectra. Ring A conformations were determined from the two‐ and three‐bond proton‐proton couplings and NOE measurements. The utility and limitations of extended Karplus‐type equations, the effect of cyclopropyl groups on vicinal and geminal couplings and cyclopropane‐induced chemical shifts are discussed.
Conformational analysis of oligomeric flavanoids. 2—methyl ether acetate derivatives of profisetinidins
Authors: Steynberg Jan P. , Brandt E. Vincent , Ferreira Daneel , Helfer Carin A. , Mattice Wayne L. , Gornik Dominika , Hemingway Richard W.
Published: May 2005

The profisetinidins are the most important polyflavanoids of commerce, making up the major constituents of wattle and quebracho tannins. Even within the dimeric profisetinidins, substantial complexity exists because of stereo‐, regio‐, rotational and conformational isomers. Definition of the stereochemistry of the upper and lower flavan units, the location of the interflavanoid bond, the conformation of the heterocyclic rings in the upper and lower flavan units and the conformations of major and minor rotational isomers in a series of methyl ether acetate derivatives of dimeric profisetinidin diastereomers is possible by application of COSY and NOE experiments. All compounds studied were present in two rotameric forms with the more compact conformation favored. The heterocyclic ring in the upper chain extender unit was predominantly in an E‐conformation (i.e. half‐chair in 2R,3S isomers and a ‘reverse’ half‐chair in the 2S,3R isomers). The heterocyclic ring conformation of the terminal cate‐chin unit, although mostly in an E‐conformation, was often represented by significant proportions of A‐conformers.
1H and 13C NMR spectra of the methanolic allomerization products of 132(R)‐chlorophyll a
Authors: Hyvärinen Kristiina , Helaja Juho , Kuronen Pirjo , Kilpeläinen Ilkka , Hynninen Paavo H.
Published: May 2005

The spontaneous autoxidation (allomerization) of 132(R)‐chlorophyll a in methanol produces seven main products containing three epimer pairs. The 1H and 13C NMR spectra of these products in acetone‐d6 were recorded on a 500 MHz spectrometer and fully assigned using two‐dimensional HMQC and HMBC techniques. The absolute configurations of the oxidized carbons, originally C‐132, were determined using the ROESY technique. In comparison with 132(R)‐chlorophyll a, the steric repulsion between the C‐17 side‐chain and the bulky substituents of the oxidized C‐132 causes steric strain in the chiral part of an allomer, relieved by conformational changes in rings D and E and to a lesser extent also in the whole macrocycle. These changes were estimated for each allomer from the Δδ values of the carbon and proton resonances and from proton‐proton coupling constants. Information about the orientation of the front part of the phytyl chain in 132(R)‐chlorophyll a and its methanolic allomers was obtained by analysing the variation in the form of the P1‐CH2 signal.
Oxygen‐17 and carbon‐13 NMR studies of diarylketenes
Authors: Cerioni Giovanni , Plumitallo Antonio , Frey Joseph , Rappoport Zvi
Published: May 2005

Natural abundance 17O and 13C NMR spectra for eleven diarylketenes are reported. 17O shifts show invariance with para substitution and a shielding due to ortho substitution. A buttressing effect is observed for bis(2,3,4,5,6‐pentamethylphenyl)ketene. A comparison between ketenes and isocyanates is made. The importance of cylindrical symmetry for half‐height linewidths is discussed.
Nitrogen NMR assessment of interactions between nitroso, cyano and acetyl groups across aliphatic systems
Authors: Witanowski Michal , Biedrzycka Zenobia , Konopski Leszek , Grela Karol
Published: May 2005

The nitrogen NMR shieldings (Δσ, equivalent to —Δδ on the frequency scale of chemical shifts) of the NO group in nitrosoalkanes are shown to be a sensitive probe to electron‐withdrawing effects of substituents and to steric strain effects. The former produce high‐field (low‐frequency) shifts, which can amount to about 90 ppm, while the latter result in considerable low‐field (high‐frequency) shifts of the NO nitrogen resonance. The CN nitrogen shieldings show less pronounced low‐field (high‐frequency) shifts under the influence of electron acceptors. The signs and magnitudes of the observed effects are explained in terms of semi‐empirical molecular orbital calculations of the shieldings and molecular mechanics evaluations of strain energies. The overall picture of relationships between the NO and CN nitrogen shieldings and electron charge migration within the molecules concerned is in accord with that obtained in earlier studies of solvent‐induced effects on the nitrogen shieldings in alkyl cyanides and nitro compounds.
13C and 15N NMR study of substituted 1,2,4‐triazines
Authors: Kolehmainen Erkki , Šaman David , Pískala Alois , Masojídková Milena
Published: May 2005

13C and 15N NMR spectra of eight substituted 1,2,4‐triazines were measured and assigned. The assignments of the 13C NMR spectra were based on the substituent chemical shifts and nJ(C,H) coupling constants. 15N NMR chemical shifts generally showing well separated ranges were assigned by the proton coupled 15N NMR spectra. 15N NMR chemical shifts of N‐4 in 3‐ and 5‐methoxy or ‐thiomethyl‐substituted 1,2,4‐triazines were found to be related significantly (confidence level >99%) with the π‐charge at N‐4 calculated by a semi‐empirical molecular orbital (AM1) procedure. For the 15N NMR chemical shifts of N‐1 and N‐2, no reliable correlations with the molecular electronic properties such as AM1 π‐charges and ionization potentials (—EHOMO) were found.
1H (300 MHz) and 13 C NMR spectral assignments for diisocyanoadociane
Authors: König Gabriele M. , Wright Antony D.
Published: May 2005

Complete 1H and 13C NMR data are reported for the marine‐derived natural product diisocyanoadociane, based on COSY, NOESY, XHCO, HMQC, HMBC and INADEQUATE measurements. The 15N NMR data for this compound are also reported.
One‐ and two‐dimensional NMR study of resol phenol—formaldehyde prepolymer resins
Authors: Fisher Thomas H. , Chao Ping , Upton Cindy G. , Day Anthony J.
Published: May 2005

A one‐ and two‐dimensional NMR study was performed on three commercial resol phenol—formaldehyde (PF) prepolymer resins. 1H, 13C, CSCM and DQF COSY NMR spectral data, in acetone‐d6, were obtained on each resin and on PF model compounds: phenol, five methylolphenols, four diphenylmethanes, two formals, two dibenzyl ethers and two dibenzylamines. Gated‐decoupled 13C experiments, using 2,4,6‐trimethylphenol as internal standard, were used to quantitate the major components present in each of the three resins. The major chemical differences of the three resins were noted. A DQF COSY method was developed that allowed the qualitative identification of most of the major phenolic components present in each of the PF resins.
Submicromole structure elucidation: Cryptolepicarboline—a novel dimeric alkaloid from Cryptolepis sanguinolenta
Authors: Sharaf Maged H. M. , Schiff Paul L. , Tackie Albert N. , Phoebe Charles H. , Howard Layne , Meyers Carol , Hadden Chad E. , Wrenn Susan K. , Davis Ann O. , Andrews C. Webster , Minick Doug , Johnson Robert L. , Shockcor John P. , Crouch Ronald C. , Martin Gary E.
Published: May 2005

Cryptolepis sanguinolenta (Lindl.) Schlechter (Asclepiadaceae), a shrub indigenous to West Africa, has been employed by traditional healers in the treatment of various fevers, including malaria. Column chromatography of the alkaloid fraction obtained from a defatted ethanolic extract of the roots of the plant afforded the previously characterized alkaloids cryptolepine, quindoline and cryptospirolepine. Continued extensive column chromatography, followed by preparative high‐performance liquid chromatography, resulted in the isolation of nine new alkaloids, including approximately 100 μg of a novel indoloquinoline‐β‐carboline dimeric alkaloid, cryptolepicarboline. The structure was elucidated through the use of a combination of spectroscopic techniques which included UV, Fourier transform, electron impact mass spectrometry, and 500 MHz NMR spectroscopy. NMR data included 1D 1H and 13C reference spectra, the latter recorded in 40 μl of DMSO‐d6 using a new Varian heteronuclear Nano‐probe and in 140 μl of DMSO‐d6 using a Nalorac carbon‐optimized microprobe. These 13C NMR spectra allow the first direct comparison of these two probe formats. Homonuclear 2D NMR data acquired included both COSY and ROESY spectra. The homonuclear 2D experiments were variously performed in both a homonuclear Nano‐probe and micro‐inverse detection probes. Heteronuclear shift correlation experiments included HMQC, HMBC and IDR (inverted direct response)‐HMQC‐TOCSY spectra, which were uniformly performed using a 500 MHz Nalorac micro inverse‐detection probe.
Computerized analysis of 2D INADEQUATE spectra to assign chemical shifts in aromatic compounds
Authors: Orendt Anita M. , Dunkel Reinhard , Horton W. James , Pugmire Ronald J. , Grant David M.
Published: May 2005

A computerized analysis of a single 2D INADEQUATE spectra assigns all of the 13C chemical shifts in fairly complex aromatic systems. Without the aid of the computer this information is often difficult, if not impossible, to retrieve owing to overlap of the signals in the double quantum dimension. In addition, the use of the computerized analysis allows for the interpretation of INADEQUATE spectra with much lower signal‐to‐noise ratios than are practical if the analysis were to be done visually. Finally, narrowing the spectral window to a subset of the entire spectrum and the companion advantages are demonstrated. The assignments of the aromatic chemical shifts in 2‐methoxydibenzofuran, 6‐methylchrysene, 1‐decylpyrene, and 7‐methylbenzo[a]pyrene illustrate the power of automated pattern recognition methods while supplying previously unavailable chemical shift assignments on these complex fused polycyclic aromatic systems.
Two‐dimensional nutation echo 75As NQR spectroscopy in antiferroelectric NH4H2AsO4 using the maximum entropy method
Authors: Kątowski P. , Maćkowiak M.
Published: May 2005

With a view to developing efficient methodologies for the evaluation of the asymmetry parameter of the electric field gradient (EFG) tensor from polycrystalline specimens, an alternative approach which involves two‐dimensional spin‐echo NQR data processing by the maximum entropy method (MEM) is presented. The superiority of MEM over the traditional fast Fourier transform (FFT) method is demonstrated by the analysis of two‐dimensional NQR data obtained using the modified pulse sequence. The method has been successfully applied to the determination of the EFG tensor at the 75As site in the antiferroelectric phase of polycrystalline ammonium dihydrogenarsenate (ADA), where conventional nutation spectroscopy fails owing to the large NQR linewidth.