bluuebunny/crossref_metadata_2025 huggingface dataset:
31P NMR enantiomeric purity determination of free 1‐aminoalkylphosphonic acids via their diastereoisomeric Pd(II) complexes
Authors: Głowacki Zdzisław , Topolski Marek , Matczak‐Jon Ewa , Hoffmann Maria
Published: May 2005

A convenient 31P NMR method for determining the enantiomeric excess of free 1‐aminoalkylphosphonic acids is presented. It was found by NMR that the interaction of PdII ions with 1‐aminophosphonate ligands (L) yields, in a non‐diastereoselective manner, diastereoisomeric chelate pairs (PdL2) observable in alkaline D2O solutions. The chelate complexes give two peaks in the 31P NMR spectra; one corresponds to the chiral species e (both ligands are R or S enantiomers) and the second to the meso forms (R and S ligands). The shapes of these peaks and the differences in the chemical shifts for the species (Δδ) depend on the temperature and the resonance frequency, typical for a dynamic process. Under the experimental conditions used (273–293 K and 40.48 or 121.5 MHz) Δδ values in the range 0.03–0.18 ppm were obseved. The separation of the 31P NMR signals of eight of the ten investigated racemic acids allowed the determination of the enantiomeric purity. The measured enantiomeric excess of an enantiomerically enriched sample of 1‐aminobenzylphosphonic acid (prepared by weighing) was in excellent agreement with the expected value.
Pseudolaric acid B: NMR assignments, conformational analysis and cytotoxicity
Authors: Hamburger Matthias O. , Shieh Hui‐Ling , Zhou Bing‐Nan , Pezzuto John M. , Cordell Geoffrey A.
Published: May 2005

The proton and carbon spectra for the fertility‐regulating agent, pseudolaric acid B (1), have been assigned using a combination of one‐ and two‐dimensional NMR spectroscopic techniques. NOE difference measurements revealed an unexpected conformation of the molecule, which could only be explained by a strained conformation of the six‐membered lactone ring. Molecular forcefield calculations confirmed the presence of a low‐energy conformer having the lactone ring in a half‐planar conformation. The solution conformation is closely related to the solid‐state conformation. Evaluation in a broad range of human cell lines established that 1 is a general cytotoxic agent.
Proton and carbon‐13 NMR study of scopoline and its derivatives
Authors: Scheiber P. , Nádor K.
Published: May 2005

The full assignment of the 1H and 13C NMR spectra of scopoline and its derivatives are reported. The spectral data also indicate the C‐6 configuration of the derivatives.
29Si and 13C NMR spectra of alkenyl‐ and alkynyl‐trimethylsilanes
Authors: Al‐Hassan Mohammed I. , Al‐Najjar Ibrahim M. , Al‐Oraify Ibrahim M.
Published: May 2005

29Si and 13C chemical shifts in substituted alkenyl‐ and alkynyl‐trimethylsilanes have been recorded and assigned. The 13C NMR study of R‐alkynyltrimethylsilanes gave new evidence for pπ‐dπ bonding or an equivalent interaction between the bonded carbon and silicon atoms. In addition, the 29Si and 13C NMR spectra of XC6H4SiMe3 [X = p‐CH3, p‐CH3O, m‐CH3O, H] were recorded, assigned and compared with those of the above‐mentioned compounds.
Single‐crystal electron‐spin resonance study of the 4‐phenyl‐1,2,3,5‐dithiadiazolyl radical
Authors: Lee F. L. , Preston K. F. , Williams A. J. , Sutcliffe L. H. , Banister A. J. , Wait S. T.
Published: May 2005

Single crystals of 4‐phenyl‐1,2,3,5‐dithiadiazolium trithiatriazinide magnified image, prepared by the reduction of S5N5+AlCl4− in SO2 with magnified image, contain a trace paramagnetic impurity which is shown by EPR spectroscopy to be the dithiadiazolyl free radical magnified image. The g and 14N hyperfine tensors of the radical were deduced from measurements made throughout three mutually orthogonal planes of crystallographically aligned specimens: g = (2.0011, 2.0075, 2.0197); 14N(2) = (37.1, 11.3, 3.4 MHz.). Within experimental error, the two nitrogen hyperfine interaction tensors are collinear and have their maximum principal value aligned parallel to gmin and perpendicular to the plane of the host cation. The results are interpreted in terms of a planar π‐radical which substitutes for the planar host cation, and which has considerable unpaired spin density in N(2px) atomic orbitals directed perpendicular to the heterocyclic ring.
13C NMR chemical shifts of the carbon atoms of the methoxymethyl group of di‐ortho‐substituted aromatic methoxymethyl ethers
Authors: Kaufman Teodoro S. , Sindelar Robert D. , Jürgens Alex R.
Published: May 2005

Complete 13C spectral assignments of 28 aromatic methoxymethyl ethers bearing different substituents and substitution patterns were made. While meta‐, para‐ or mono‐ortho‐substitution did not significantly affect the 13C resonances of the carbon atoms of the methoxymethyl group, di‐ortho‐substitution produced the deshielding of both carbons. This effect was more pronounced on the methylene carbon atom.
Carbon‐13 NMR chemical shift assignment of neoflavonoids
Authors: Delle Monache Giuliano , Messana Irene , Botta Bruno , Gács‐Baitz Eszter
Published: May 2005

The 13C NMR resonances of some 5,7‐dihydroxy‐ and 5,7‐dimethoxy‐4‐arylcoumarins were assigned by two‐dimensional NMR experiments (HETCOR and LONG‐RANGE HETCOR) on some key compounds.
Natural abundance one‐bond 13C13C coupling constants and unambiguous assignments of 13C NMR chemical shifts of dithieno[b,d]pyridines; a multivariate data analysis
Authors: Gronowitz Salo , Hörnfeldt Anna‐Britta , Yang Youhua , Edlund Ulf , Eliasson Bertil , Johnels Dan
Published: May 2005

The one‐bond 13C13C coupling constants (1JCC) in all nine possible dithieno[b,d]pyridines were measured at natural isotope abundance by using the INADEQUATE pulse sequence technique. The unambiguous assignments of the 13C NMR shifts of these compounds are also reported. Assignments are based on proton decoupled 13C spectra, heteronuclear correlation spectra (HETCOR) and 1D‐INADEQUATE 13C NMR spectroscopy. The effect of the fusion pattern and the influence of the heteroatoms in the ring skeleton on the NMR parameters are discussed. By a multivariate principal components data analysis, it was shown that the magnitude of 1J(CC) of the pyridine subunit could be satisfactorily predicted from shift data, the azomethine CH coupling constant and MNDO bond orders. The last parameter gave only a minor contribution to the coupling variability.
Empirical computation of 13C NMR chemical shifts
Authors: Jaime Carlos
Published: May 2005

An equation correlating 13C NMR chemical shifts and the global van der Waals energy of the carbon atoms (rms deviation δ ≤ 2.6 ppm) in aliphatic hydrocarbons, alcohols and chlorinated derivatives was derived. Molecular mechanics calculations have been used to determine the global van der Waals energy.
Sign inversion of 1J(207Pb13C) coupling constants and correlations between 1J(207Pb13C) and 1J(119Sn13C) values for comparable lead and tin compounds
Authors: Wrackmeyer Bernd , Horchler Klaus
Published: May 2005

Relative signs of 1J(207Pb13C) and 2J(207Pb1H) were determined for numerous methyllead derivatives by observing the 207Pb satellites in two‐dimensional (2D) 13C/1H heteroscalar correlated NMR spectra. The compounds studied include the species [R3Pb]Li (R = Me, 1a, Et 1b), Me3PbSiMe3 (2), [Me3PbBH3]Li, several alkenyltri‐methyllead compounds and some heterocyclics. Together with the linear correlation between 1J(207Pb13CMe) and 1J(119Sn13CMe) for the corresponding tin compounds, this enables the prediction of the absolute sign of 1J(207Pb13CMe). An analogous linear correlation 1J(207Pb13CC=)/1J(119Sn13CC=) exists which explains some apparently anomalous values reported in the literature, e.g. for [Ph3Pb]Li and for an intramolecular‐base‐stabilized plumbylene. The two coupling constants, 1J(207Pb13CMe), for the Me2Pb group in a 2,5‐dihydro‐1,2,5‐azoniaplumbaboratole are of opposite sign, giving the first example of this type of behaviour for any dimethyl element fragment. In the case of 2 the negative sign of 1J(207Pb29Si) [reduced coupling constant 1K(207Pb29Si) > 0] has been deduced from the tilt of the 207Pb satellites in the 2D 29Si/1H heteroscalar correlated NMR spectrum. A positive sign of 1J(207Pb11B) follows from the consistent trend observed for the reduced coupling constants 1K(M11B) and 1K(M13C) (M = 13C, 29Si, 119Sn, 207Pb) in the series of compounds [Me3MBH3]Li and Me4M, respectively.
Selective excitation of a single CSA side‐band family and a complementary experiment for discriminating CSA‐averaged resonances
Authors: Boudot D. , Canet D. , Tekely P. , Brondeau J.
Published: May 2005

The DANTE‐Z pulse train [(θ)x‐τ‐(θ)x‐τ]n (π/2) (Acq)±, applied to solid‐state samples in an asynchronous manner with respect to the rotor period of the magic‐angle spinning, is able to extract the spectrum of a single CSA (chemical shift anisotropy) side‐band family without any intensity alteration. The effects of such a selectivity sequence is described by means of a phenomenological approach. A related method, based on selective destruction of magnetization via T2 processes, is proposed for retaining only those resonances for which CSA effects are totally averaged out by magic‐angle sample spinning.
Deuterium isotope effects and bonding in carbonylvanadium complexes
Authors: Rehder Dieter , Hoch Martin , Jameson Cynthia J.
Published: May 2005

The effects of one‐bond and two‐bond 2H, 13CO and C18O isotope shifts on 51V shielding in various carbonyl–Cp–vanadium complexes (Cp = n5‐cyclopentadienyl) are reported and discussed with respect to the sensitivity of 51V shifts to bond extensions, and the rovibrationally averaged values of such bond extensions. These isotope effects provide some insight into the bonding situation in these complexes. It is shown that the rate‐determining step in the reaction between V(CO)6 and C5H5D, which leads to CpV(CO)4, is not subject to a kinetic isotope effect. The deuterium solvent isotope effects on 51V shielding in [V(CO)6]‐ and [VO4]3‐ are also investigated.
Tetrahedral, chelated, silver(I) diphosphine complexes. Rapid measurements of chemical shifts and couplings by two‐dimensional 31P–{109Ag} NMR spectroscopy
Authors: Berners‐Price Susan J. , Sadler Peter J. , Brevard Christian
Published: May 2005

The 109Ag NMR spectrum of [Ag(Ph2PCHCHPPh2)2]NO3, a complex with antimicrobial and antitumour activity, was obtained using a retro‐INEPT two‐dimensional 31P–{109Ag} pulse sequence. This allowed the measurement of the 31P and 109Ag chemical shifts and the 1J(109Ag,31P) coupling constant in a single 2 h experiment and offered a considerable signal‐to‐noise gain compared with 109Ag–{31P} INEPT measurements.
Assignment of 13C NMR spectra of multisubstituted aromatic compounds using a combination of extended DEPT and COLOC illustrated through the total assignment of SR2640
Authors: Rastrup‐Andersen Niels , Aagaard Grethe
Published: May 2005

The combination of Extended DEPT and COLOC was found to be a good alternative to the more time‐ and sample‐consuming INADEQUATE technique for assigning the 13C NMR spectra of multi‐substituted aromatic compounds. The use of the method is illustrated by spectra of the leukotriene D4/E4 antagonist SR2640 {2‐[3′‐(2″‐quinolylmethoxy)phenyl]aminobenzoic acid} as the potassium salt. Total assignments of the 1H and 13C NMR spectra are given.
Complete 13C and 1H NMR assignments for a series of aromatic C‐ring derivatives of dehydroabietic acid
Authors: Jurgens Alex R. , McChesney James D.
Published: May 2005

Complete 13C and 1H NMR spectral assignments for a series of derivatives of the naturally occurring C‐ring aromatic diterpene resin acid dehydroabietic acid have been made. The use of a combination of 1D and 2D NMR techniques allowed mostly unambiguous assignments of all 13C resonances. 1H resonances were also assigned.
Substituent effects on the 13C NMR chemical shifts of 1‐hydroxyalkylphosphonic acids
Authors: Glowacki Zdzisław , Hoffmann Maria
Published: May 2005

13C chemical shifts and 31P,13C coupling constants are reported for nine 1‐hydroxyalkylphosphonic and two additional phosphonic acids. The α‐substituent‐induced chemical shifts (α‐SCS) of the phosphonate group were calculated and their non‐additivity was observed. Good linear correlations exist between the chemical shifts and also between the α‐SCS parameters of 1‐hydroxyalkylphosphonic acids and the respective values of analogously constituted 1‐aminoalkylphosphonic acids.
13C NMR chemical shifts and substituent effects transmission in 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes
Authors: Gandhi R. P. , Ishar M. P. S. , Kumar Sudhir
Published: May 2005

13C NMR chemical shifts were determined for all carbons in a number of 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes [aryl = C6H5, C6H4CH3‐p, C6H4F‐p, C6H4Cl‐p, C6H4Br‐p, C6H4CN‐p, C6H4NO2‐p, C6H4OCH3‐p, C6H3(OCH3)2‐m, p and α‐furyl]. Substituent chemical shift (Δδ13C) values for C‐1, C‐3, C‐4, C‐5, C‐6, C‐1′, C‐2′, C‐3′ and C‐4′,8′ were correlated with various Hammett parameters by singleparameter analysis. The correlations revealed that the substituent effects are transmitted across three π‐bonds in conjugation with the aryl ring. Dual‐substituent‐parameter treatment of the substituent chemical shifts revealed that resonance plays a major role in the substituent effect transmission. Hammett parameters were also derived for the α‐furyl substituent.
13C NMR of coumarins. IV—Furanocoumarins
Authors: Macias F. A. , Massanet G. M. , Rodriguez‐Luis F. , Salvá J.
Published: May 2005

13C NMR data for several linear furanocoumarins are reported. The β, γsyn and δ effects of a 5‐oxygenated function on the coumarinic skeleton were measured. A spectroscopic criterion for distinguishing between C‐5 and C‐8 oxygenated, between C‐5 oxygenated, C‐8 alkylated and C‐5 alkylated, C‐8 oxygenated linear furanocoumarins and between C‐5 oxygenated linear or angular furanocoumarins is proposed.
NMR spectroscopic identification of (1S, 4R, 6R)‐ and (1S, 4R, 6S)‐1,3,3‐trimethyl‐2‐oxo‐6‐(2‐oxopropyl)bicyclo[2.2.2]octane, key intermediates towards the total synthesis of (+)‐norpatchoulenol
Authors: Liu Hsing‐Jang , Ralitsch Milan
Published: May 2005

High‐field NMR studies of (1S, 4R, 6R)‐ and (1S, 4R, 6S)‐1,3,3‐trimethyl‐2‐oxo‐6‐(2‐oxopropyl)bicyclo[2.2.2]octane were carried out by one‐ and two‐dimensional methods. The stereochemical aspects of these molecules were studied through the application of the nuclear Overhauser effect and stereospecific coupling constants. Unambiguous 1H and 13C chemical shift assignments have been made on the basis of two‐dimensional homonuclear (1H–1H) and heteronuclear (1H–13C) correlation spectroscopy, APT, INAPT and broad‐band proton decoupling experiments.
Dependence of 13C NMR methoxy substituent chemical shift values on π‐bond orders of fused aromatic compounds
Authors: Joseph‐Nathan Pedro , García‐Martínez Cirilo , Morales‐Ríos Martha S.
Published: May 2005

The substituent chemical shift values induced by the methoxy group at the two ortho positions of aromatic compounds which include naphthalenes, quinolines, indoles, coumarins, flavones and benzofurans were linearly correlated with π‐bond orders, affording the equation Δδortho(13C) = ‐98.68Pπ + 50.38 (correlation coefficient = 0.929; root mean square error = 1.95 ppm) when 40 pairs of values are considered. Elimination of six points corresponding to ring‐junction quaternary carbons improves the correlation coefficient to 0.961 (root mean square error = 1.4 ppm) for the equation Δδortho(13C) = ‐126.85Pπ + 69.66.
Sulphur‐33 and oxygen‐17 NMR studies of sulpholane in acetic acid and related solvents
Authors: Ali Ahmed A. M. , Harris Robin K. , Belton Peter S.
Published: May 2005

Sulphur‐33 NMR spectra were obtained for sulpholane in acetic acid, trifluoroacetic acid, methyl acetate and methyl trifluoroacetate over the entire solution range and at a variety of temperatures. Oxygen‐17 NMR spectra were recorded for both components of each solution. The line width and chemical shift data are discussed in terms of molecular interactions and viscosity variations. Some variable‐temperature measurements are included, as are some values of 13C spin‐lattice relaxation times. It is concluded that there is an interaction, probably protonation, between sulpholane and trifluoroacetic acid, although occurring to only a small extent, which is not shown by the other solutions. The 33S and 17O line widths of sulpholane are peculiarly sensitive to the interaction.
15N and 13C NMR study of acylated hydrazines. The instability of trifluoroacethydrazide in the solid state
Authors: Fritz Hans , Kristinsson Haukur , Mollenkopf Max , Winkler Tammo
Published: May 2005

Trifluoroacethydrazide is unstable even in the solid state with respect to hydrazonium N,N′‐ditrifluoroacetyl hydrazinate, as shown by 15N and 13C NMR spectroscopy. The 1H, 13C and 15N NMR data and rotamer distributions of formyl‐, acet‐ and trifluoroacet‐hydrazide and of N,N′‐diformyl‐, N,N′‐diacetyl‐ and N,N′‐ditrifluoroacetyl‐hydrazine are reported and compared with the results of earlier investigations. A conformational dependence is observed for 1J(NH) and 2J(NH) in the formylhydrazides and of 1J(NH), 2J(NH) 3J(NH) in the N,N′‐diformylhydrazines. The conformational dependence of 2J(CH) in formamide, reported in the literature, however, could not be confirmed.
NMR spectra of the porphyrins. 38—Conformational analysis of azacycloheptane and azacyclooctane using a novel cobalt(III) porphyrin shift reagent
Authors: Abraham Raymond J. , Medforth Craig J.
Published: May 2005

A novel NMR shift reagent, cobalt(III) meso‐tetraphenylporphyrin (CoTPP) was used to determine the conformations of azacycloheptane and azacyclooctane ligands complexed to the metalloporphyrin. Using the observed ring current shifts and a previously calibrated ring current model, the best agreement between the observed and calculated ring current shifts for azacycloheptane was obtained for a chair conformation, in agreement with previous theoretical and experimental studies on the conformational stability of seven‐membered rings. The ring current shifts for azacyclooctane are best interpreted in terms of a mixture of many conformations. These results suggest that CoTPP may be useful as a probe of other conformationally mobile ligands.
Assignment of C‐2 and C‐4 of zearalenones
Authors: Pathre S. V. , Khadikar P. V. , Mirocha C. J.
Published: May 2005

Assignments of the hydroxylated aromatic carbons C‐2 and C‐4 of zearalenone and its derivatives are reported. The C‐2 carbon is more deshielded than C‐4 for zearalenones in which the C‐2 hydroxy group is intramolecularly hydrogen‐bonded to the C‐12 lactone carbonyl.
Use of long‐range 1H, 13C correlation experiments (COLOC) for the assignment of the 13C NMR spectrum of chloroquine and related 4‐aminoquinoline compounds
Authors: Moreau S. , Veignie E.
Published: May 2005

The 13C NMR spectra of chloroquine and related 4‐aminoquinolines have been completely assigned by the use of 1H‐13C correlation sequences based on direct and long‐range J(CH) coupling constants in conjunction with DEPT.
1H and 13C NMR aromatic solvent‐induced shifts of n‐alkanes
Authors: Nikki Kunio
Published: May 2005

The 1H and 13C NMR spectra of a series of n‐alkanes (C5‐C32) were measured in CCl4, CDCl3, C6D6, C6H5Cl and C6D5CD3 and the aromatic solvent‐induced shifts (ASIS) are discussed. The chemical shifts of the inner methylene protons show a steady downfield shift as the carbon number of the n‐alkane increases, while the shifts of the methyl protons are smaller than those of the inner methylene protons in aromatic solvents. The ASIS of the outer carbons are larger than those of the inner carbons up to the sixth carbon from the end. The ASIS of the sixth and further inner carbons of the short chains are larger than those of the long chains. These results suggest that n‐alkanes have a folded structure in aromatic solvents and that the degree of folding increases with increasing chain length.
Intrinsic deuterium isotope effects of deuteriated tert‐butyl groups on the 13C NMR spectra of aromatic compounds
Authors: Balzer Hartmut H. , Berger Stefan
Published: May 2005

The 3Δ‐deuterium isotope effects of partially and fully deuteriated tert‐butyl groups on the 13C NMR spectra of tert‐butylbenzene and derivatives are discussed in detail. It is shown that they correlate with the chemical shift of C‐1 of the aromatic ring. It has been demonstrated that when deuterium is replaced with some other substituents, the SCS values of these substituents show a parallel behaviour to the deuterium isotope effects. It is concluded that, for the compounds studied, deuterium isotope effects and substituent chemical shifts can be described on a common basis.
Two‐dimensional INADEQUATE 13C NMR studies of maleopimaric acid, the diels–alder adduct of levopimaric acid and maleic anhydride, and of abietic acid
Authors: Kruk C. , de Vries N. K. , van der Velden G.
Published: May 2005

Two‐dimensional INADEQUATE 13C NMR was used to establish firmly the carbon‐carbon connectivities present in abietic acid and maleopimaric acid, i.e. the adduct of levopimaric acid and maleic anhydride. This information leads to unambiguous assignments for the 20 and 24 carbon resonances of abietic acid and maleopimaric acid, respectively. Proton‐carbon chemical shift correlation and NOE experiments further revealed the three‐dimensional structure of maleopimaric acid.
1H NMR assignment and conformational analysis of glucitol: Comparison with maltitol
Authors: Hoffman Roy E. , Rutherford Trevor J. , Mulloy Barbara , Davies David B.
Published: May 2005

The 1H NMR spectrum of glucitol in D2O solution contains eight strongly‐coupled multiplets covering a chemical shift range of about 0.21 ppm. The spectrum is severely complicated by second‐order effects and was assigned by a combination of 2D NMR experiments and extensive spin simulation of the 1D spectra. The magnitudes of the spin coupling constants were analysed in terms of preferred conformations about each bond in the backbone of glucitol, and the results were compared with those found for maltitol in solution, with crystal conformations of both glucitol and maltitol and with low‐energy conformations computed using the MM2CARB force field. The results show a surprising degree of agreement between computed low‐energy conformations and those observed in the crystal, but little correspondence with conformations observed by NMR in solution. Although maltitol is derived from glucitol sustituted in the 4‐position with the bulky α‐D‐glucopyranose moiety, NMR measurements indicate approximately free rotation about all bonds in the glucitol moiety of maltitol. This is in contrast to glucitol, where the proton‐proton trans conformer predominates (74%) for the C4–C5 bond which, in turn, stabilizes the gauche‐gauche conformer of the adjacent C5–C6 bond (53%) and destabilizes the trans conformer of the C3–C4 bond (3%).

It is found from molecular modelling studies that steric factors alone cannot explain these results, and it is postulated that intramolecular hydrogen bonding stabilizes the local conformations in glucitol whereas disruption of the hydrogen‐bond network occurs as a result of substitution of the glucitol moiety in maltitol.
1H and 13C NMR determination of the relative stereochemistry of the diastereomers resulting from the reaction of sily enol ethers with the 1‐ethoxy‐1‐propargylium dicobalt hexacarbonyl cation
Authors: Montaña Pedrero Angel M. , Nicholas Kenneth M.
Published: May 2005

The application of 1H and 13C NMR correlations and phase‐sensitive NOESY in the stereochemical assignment of four diastereoisomers of hexacarbonyl{μ‐η4‐[2,4‐dimethyl‐2‐(1‐ethoxy‐2‐propyn‐1‐yl)‐8‐oxabicyclo [3.2.1] octan‐3‐one]}dicobalt‐(CoCo) is reported.
Spectral artifacts in heteronuclear chemical shift correlation experiments with homonuclear decoupling via a constant evolution time
Authors: Swapna G. V. T. , Rao N. Sambasiva , Ramachandran R.
Published: May 2005

Experimental and theoretical studies carried out to investigate the influence of strong coupling effects in the spectra generated through the commonly used heteronuclear chemical shift correlation (HETCOR) sequences involving a constant evolution time are reported. It is seen that the spectra generated via such sequences are prone to artifacts of appreciable intensity. Failure to recognize these can result in the misinterpretation of spectral data.
Dependence of vicinal 31P–31P and 31P–13C coupling constants on the dihedral angle of α, β‐diphosphonates
Authors: Grossmann G. , Lang R. , Ohms G. , Scheller D.
Published: May 2005

Several α,β‐diphosphonates with a norbornane or cyclohexane skeleton were prepared, and the 31P‐31P coupling constants over three bonds for the ethyl or methyl esters, the acid and anion were obtained from the 13C NMR spectra or the 13C satellites in the 31P NMR spectra. The 3J(PP) values cover a range of about 90 Hz and are therefore well suited for conformational and configurational analysis. The dependence of 3J(PP) on the dihedral angle is well reflected by an extended Karplus relationship: 3J(PP) = A + B cos φ + C cos 2φ + D cos 3φ, with different parameters for the esters, acids and anions. For trans and gauche arrangements of the α,β‐diphosphonic acids the dependence of the P‐P coupling constants on the degree of titration is given. Investigations of the dependence of 3J(PC) on the PCCC dihedral angle show that a good curve fitting is achieved using the Karplus relationship 3J(PC) = AA + AB cos φ + C cos 2φ. A comparison of these curves with published data indicates smaller coupling constants for φ ≈ 0°. The coefficients of the Karplus equation for the 3J(PC) values obtained for esters are similar for acids and anions.
13C nuclear magnetic resonance spectra of several podocarpane and cassane diterpenoids
Authors: Abad A. , Agulló C. , Arnó M. , Domingo L. R. , Zaragozá R. J.
Published: May 2005

The 13C NMR spectra of several diterpenic derivatives having the podocarpane and cassane skeleton were recorded and interpreted. The most significant effects due to substituent orientation, B/C ring junction stereochemistry and conformational changes are briefly discussed.
Structure of methylenecyclopropane in a liquid crystal by 1H and 13C NMR
Authors: Turku Taoufik , Haloui Ezzeddine
Published: May 2005

The 1H and 13C NMR spectra of methylenecyclopropane, both in the isotropic phase and in the Merck IV nematic phase, were analysed. The relative signs of the 13CH scalar coupling constants were determined. The complete geometry deduced from this study was compared with that from a microwave study, and the discrepancies are discussed.
1H and 13C NMR studies of the protonation of isomeric methoxysulmazole analogues
Authors: Lindon J. C. , Williams J. M. , Barraclough P. , King W. R. , Nobbs M. S.
Published: May 2005

The major protonation sites of six cardiotonic isomeric 2‐aryl‐n‐methoxy‐1H‐imidazo[4,5‐b]‐ and ‐[4,5‐c]‐pyridines (n = 4–7) were determined by 1H and 13C NMR methods. All the 1H‐imidazo[4,5‐c]pyridines and the 7‐methoxy derivative of sulmazole were found to protonate at the pyridyl nitrogen. Protonation occurred at the imidazo nitrogen, however, for the 5‐ and 6‐methoxy derivatives of sulmazole.
13C NMR studies on radical anions. Special solvent effects
Authors: Doctorovich Fabio , Nudelman N. S.
Published: May 2005

The determination of radical ions is crucial in mechanistic studies of reactions in which single electron transfer is suspected. A 13C NMR method based on the interaction of radical anions with tetrahydrofuran (THF) molecules is presented; measurements of the broadening of the THF α‐carbon signal allow determination of the substrate concentration in the range 0.2–1.2 M. The spectacular effect observed on addition of small amounts of benzene greatly improved the method. In addition, studies of the spin‐lattice, T1, and of the transverse nuclear, T2, relaxation times and of the effects of added co‐solvents allow the proposal of the bonding situation and of the degree of coordination in the radical anion‐cation‐THF molecules' complex.
Intramolecular interactions in N‐vinyl‐2‐arylpyrroles and ‐2‐heteroarylpyrroles by 1H and 13C NMR
Authors: Afonin Andrei V. , Sigalov Mark V. , Korostova Svetlana E. , Aliev Ismail A. , Vashchenko Alexander V. , Trofimov Boris A.
Published: May 2005

The introduction of a substituent in the 3‐position of the pyrrole ring in N‐vinyl‐2‐arylpyrroles and ‐2‐heteroarylpyrroles results in an increase in the dihedral angles between the planes of the pyrrole ring and the aryl (or heteroaryl) residue, and a decrease in the dihedral angle between the planes of the pyrrole ring and the vinyl group. Introduction of the substituent in the 5‐position of the pyrrole ring has the opposite effect on these angles. For N‐vinyl‐2‐(2′‐furyl)pyrrole, some spectral data suggest the formation of a CH…O hydrogen bond between the α‐hydrogen atom of the vinyl group and the oxygen atom of the furyl ring. This is in accord with the results of quantum chemical calculations.
Determination of the enantiomeric purity of disubstituted β‐lactams by NMR spectroscopy using a chiral shift reagent
Authors: Belleney J. , Bui C. , Carriere F. J.
Published: May 2005

The enantiomeric purities of disubstituted β‐lactams were determined by 1H and 13C NMR spectroscopy using tris[3‐(trifluoromethylhydroxymethylene)‐d‐camphorato]europium(III), Eu(tfc)3, as a chiral shift reagent. Using a [Eu(tfc)3]/[lactam] ratio of 0.5, most of the resonances were split into signal pairs due to the respective enantiomers. The method gives quantitative enantiomeric compositions. 13C NMR spectroscopy is more advantageous than 1H NMR, which is of limited use owing, for example, to the significant line broadening observed in the 1H spectra at [Eu(tfc)3]/[lactam] > 0.8. Assignments of the proton and carbon signals were obtained for the two enantiomers of the complexed lactams.
Assignment of relative configurations and conformational study of acyclic diastereomeric ketones
Authors: Alvarez‐Ibarra C. , Arias‐Pérez M. S. , Moya E.
Published: May 2005

The conformational analysis and the assignment of relative configurations [(RR, SS) and (RS, SR)] to the dia‐stereomeric racemates of two acyclic ketones with two asymmetric carbons, ±‐2,2,7,7‐tetramethyl‐5,6‐diphenyloctan‐3‐one and ±‐5,5‐dimethyl‐1,3,4‐triphenylhexan‐1‐one, have been achieved by analysis of1H‐1H geminal and vicinal coupling constants, 13C–1H direct coupling constants and 13C chemical shifts. This study allows the establishment of the monoconformational character of the (RR, SS) diastereomers. The application of the empirical equation of Haasnoot et al. supports this hypothesis.
Study of lithium tetrafluoroborate–cyano complexes by NMR in thermotropic liquid crystals
Authors: Gowda G. A. Nagana , Suryaprakash N. , Weiss R. G. , Khetrapal C. L. , Diehl P.
Published: May 2005

Lithium tetrafluoroborate‐acetonitrile complexes were studied in two liquid crystals, trans,trans‐4‐n‐propyl(1,1′‐bicyclohexyl)‐4′‐carbonitrile (ZLI‐1184) and trans‐4‐pentyl‐1‐(4‐cyanophenyl)cyclohexane (S‐1114). The results indicate the formation of tetrahedral lithium‐acetonitrile complexes and the coordination of lithium from LiBF4 and LiClO4 with the cyano group of ZLI‐1184. No evidence was found to support either lithium ion complexation with S‐1114 or tetrafluoroborate ordering in any of the systems investigated.
1H and 13C NMR study of the neomenthyl halides: A very high field proton shift in the iodide
Authors: Lange Gordon L. , Gottardo Christine
Published: May 2005

Complete analyses o the 1H NMR spectra of neomethyl iodide (1), the bromide (2) and the chloride (3) are reported. Of paticular interest is the very high‐field resonance at −0.16 ppm in 1 which is assigned to H‐4. The same poton in the bromide is also found upfield at 0.78 ppm. H‐4 in these neomenthyl derivatives is tertiary and β‐antipeiplanar to the halogen atom. A similar upfield shift has been reported previously for the tertiary proton in trans‐9‐iododecalin. The reasons or these unusual shifts are not readily apparent and the 13C NMR spectra of 1 and 2, which are reported here for the first time, provide no additional clues to explain the shifts.
An empirical extension of the karplus equation
Authors: Imai Keisuke , Ōsawa Eiji
Published: May 2005

The Karplus equation is expanded to contain 11 mutually independent structural terms and 22 adjustable parameters. These terms are selected on an empirical basis and combined linearly (Eqn 4). The new equation reproduces 198 NMR vicinal 1H‐1H coupling constants determined in less polar solvents with a standard deviation of 0.33 Hz. The equation can be applied to norbornene derivatives, for which some of the previous modifications did not work well. Among new factors introduced in this modification to the Karplus‐type equation are Mullay's group electro‐negativity used in the evaluation of the α‐ and β‐substituent effects, the CC length and the CCH valence angles of the coupled HCCH system, and the through‐space interactions between a coupled proton and a non‐bonded atom within the molecule. The four most important terms are the two cosine functions, originally used by Karplus, one form of the α‐substituent effect and the CCH valence angles. These four terms alone give an accuracy of 0.42 Hz.
Direct observations of 1J(11B, 14N) coupling constants by 11B NMR spectroscopy
Authors: Ouassas Abdeljalil , Duplan Jean‐Claude , Fenet Bernard , Frange Bernard
Published: May 2005

The reaction B(NCS)4− + BX4− (X = F, Cl, Br) leads to mixed BXn(NCS) (n = 1, 2, 3) species easily detected in solution by 11B NMR. Further, with X = Cl, 1J(11B, 14N) values could be measured from the 11B NMR spectra (25.6, 24.5 and 21.4 Hz for n = 3, 2 and 1, respectively). For X = F, the relevant 1J(11B, 14N) values (24.3, 25.2 and 28 Hz for n = 3, 2 and 1, respectively) increase in the same order as the related 1J(11B, 19F) (5.5, 12.7 and 20.0 Hz, respectively). No such 1J(11B, 14N) could be resolved for X = Br.
Substituent‐Induced chemical shifts of 2‐phenylthiazolidines—1H NMR study
Authors: Umarani R.
Published: May 2005

The 1H NMR 270‐MHz spectra of substituted 2‐phenylthiazolidines were recorded and the substituent‐induced chemical shifts (SCS) of the benzylic proton plotted against σ, the correlation coefficient being 0.801 and −ρ = 10.29 Hz. Halogens show deviations in the SCS plots. When the halogen‐substituted derivatives are omitted, the correlation with σ is greatly improved. The applicability of dual‐substituent correlations using Swin‐Lupton parameters (F and R) and Taft's σ1, σR parameters has been studied.
17O NMR and molecular mechanical studies of arylmethylenemalonaldehydes
Authors: Kolehmainen Erkki , Král Vladimir
Published: May 2005

The 17O NMR spectra of six different arylmethylenemalonaldehydes were measured for various solvents and temperatures. The 17O NMR chemical shifts and line widths of the carbonyl oxygens of the malonaldehyde fragment show a clear variation in the series of monoaryl compounds studied. The differences between the 17O NMR chemical shifts of the formyl oxygens correlate well with two conformationally dependent 1H–1H and 1H–13C coupling constants for the same compounds. Molecular mechanical calculations were also performed in order to relate the present data with the conformational preferences of the malonaldehyde fragment of the arylmethylenemalonaldehydes.
Full proton NMR assignment of the reduced form of a repeat unit tetrasaccharide derived by keratanase digestion of keratan sulphate
Authors: Huckerby T. N. , Dickenson J. M. , Nieduszynski I. A.
Published: May 2005

The full assignment of the ambient‐temperature high‐field 1H NMR spectrum for the reduced form of a repeat‐unit β‐linked tetrasaccharide derived by keratanase digestion from keratan sulphate, GlcNAc(6‐SO4)13Gal(6‐SO4)14GlcNAc(6‐SO4)13Gal‐ol, was achieved using two‐dimensional COSY and RELAYED‐COSY experiments. The problem of the choice of the measurement temperature for 1H NMR spectra from keratan sulphate oligomers and polymers is discussed. A modified protocol for the preparation of keratanase‐derived oligosaccharides is proposed.
13C NMR data for chlorine‐ or nitro‐substituted azomethine dyes
Authors: Haessner Rainer , Hennig Lothar , Gaca Jerzy
Published: May 2005

The 13C NMR spectra of 1‐aryl‐substituted 3‐methyl‐2‐pyrazolin‐5‐ones and their azomethine dyes have been recorded and assigned. ortho‐Substituents (Cl and NO2) on the phenyl ring in the 1‐position of the pyrazoline moiety show a small influence on the chemical shift of the azomethine bond carbon atom, C‐4.
Determination of the barrier to CN bond rotation in captopril: Application of reference deconvolution to line‐shape analysis
Authors: Green Darren V. S. , Hillier Ian H. , Morris Gareth A. , Whalley Lesley
Published: May 2005

13C NMR was used to study the cis‐trans isomerization of 1‐[(2S)‐3‐mercapto‐2‐methyl‐1‐oxopropyl]‐L‐proline (captopril) in D2O solution over the temperature range 50–100°C. Measurements of the rate of cis‐trans interconversion were made by line‐shape analysis and saturation transfer techniques. The combined results yielded a value for the activation energy of 89 ± 2 kJ mol−1 (21.3 ± 0.5 kcal mol−1) for the C‐N bond rotation. For line‐shape analysis the experimental data were treated by reference deconvolution, using a small amount of labelled acetonitrile as reference, before processing. It was found that the deconvolution process significantly improved the reliability of the analysis.
1H and 13C NMR spectra of rac‐2,3‐bis(palmitoyloxy)propyl(2‐trimethylarsonioethyl)phosphonate, an arsenic‐containing phosphonolipid
Authors: Amato Maria E. , Irgolic Kurt J. , Junk Thomas , Pappalardo Giuseppe C. , Perly Bruno
Published: May 2005

The 1H (500 MHz), 13C (300 MHz) and 31P (202 MHz) NMR spectra of rac‐2,3‐bis(palmitoyloxy)propyl(2‐trimethylarsonioethyl)phosphonate were recorded in CDCl3 (3 M) solution. Homonuclear 1H‐1H and heteronuclear 13C–1H chemical shift correlation experiments (COSY) were performed. All resonances were assigned. The shifts of the arsenic‐containing phosphonolipid were compared with the shifts of the N‐containing phospholipids. The most significant shift differences were found for the groups directly bonded to arsenic. Spectral evidence was indicative of free rotation about the CH2 CH2 bond in the arsenocholine fragment.
Chemical shift changes on conversion of benzofurans to dihydrobenzofurans; the large effect on the proton ortho to the furan oxygen
Authors: Kalidhar Suraj B.
Published: May 2005

A comparison of the 1H NMR spectra of benzofuran and its dihydrofuran shows that the benzene proton ortho to the furan oxygen undergoes a larger change in chemical shift than those for the other protons. This observation is useful for locating the fusion sites of the furan ring in naturally occurring benzofuran derivatives.
An investigation of the keto‐enol tautomerism in 2‐acetyl‐1‐tetralone by 2D NMR spectroscopy
Authors: Agrawal Pawan K. , Thakur Raghunath S. , Frahm August W. , Schneider M.
Published: May 2005

Long‐range CH correlation and long‐range selective proton decoupling (LRSPD), together with other standard NMR techniques, led to the complete 13C and 1H NMR spectral assignments of 2‐acetyl‐1‐tetralone and demonstrated its existence in the endo‐enolic form.
Stereochemical study of a new heterocyclic system: Decahydro‐1H‐oxepino[3′,4′:4,5]isoxazolo [2,3‐a]pyridin‐1‐one
Authors: Cid P. , Figueredo M. , Font J. , Jaime C. , de March P. , Virgili A.
Published: May 2005

The stereochemistry and conformational behaviour of a new heterocyclic system obtained by the 1,3‐dipolar cyclo‐addition of 3,4,5,6‐tetrahydropyridine 1‐oxide to hex‐2‐en‐6‐olide has been studied by 1H{1H} and 13C{1H} NOE techniques and MM2 calculations.
Transmission of electronic effects through 2‐[donor]‐1‐[acceptor]‐cyclopropane
Authors: Alonso Miguel E. , Pekerar Sarah V. , Borgo Maria L.
Published: May 2005

The through‐ring conjugation between π‐donor and attractor substitutents on vicinal carbons of cyclopropane with the direct participation of the ring was assessed using proton and 13C NMR. Appropriate 1H NMR correlations were obtained between σp and δH of the trimethylene protons. However, aryl through‐space field effects were found to obscure individual conjugative effects. Conversely, the 13C NMR data implied the occurrence of competitive conjugation of π‐groups with the ring but gave no proof for the existence of the actual transmission of conjugative effects through the C‐1–C‐2 bond of the ring.
Complete assignments of the 1H and 13C NMR spectra of the macrolide antibiotic flavofungin; intramolecular hydrogen bonding and conformation
Authors: Szilágyi László , Sándor Péter
Published: May 2005

1H and 13C NMR spectra of the 32‐membered pentaene macrolide flavofungin‐I (identical with mycoticin A) in DMSO‐d6 solution were fully assigned employing a combination of various 1D and 2D homo‐ and hetero‐nuclear experiments. Secondary deuterium isotope shifts measured in the 1H NMR spectrum indicated that three of the eight hydroxyl groups are involved in intramolecular hydrogen bonds, which can lead to restricted mobility within the polyol part of the molecule. These results and inferences made from H, H coupling constants suggest that the conformation of the macrocycle is very similar to that found for roxaticin by x‐ray crystallography. All double bonds are in the E configuration, and the conjugated pentaene chain assumes a fully extended s‐trans conformation.
1H NMR chemical shift study on the stacking interaction between purine and 6‐methylpurine
Authors: Aradi Ferenc
Published: May 2005

Mutually induced proton chemical shift changes were measured for purine‐6‐methylpurine solutions in deuterium oxide at 35° C. The chemical shift vs. concentration profiles were analysed using a three‐state decomposition model based on simultaneous, competitive dimer equilibria. The association parameters for purine‐6‐methylpurine hetero‐association provide some additional information about the effect of methylation on the stacking interaction between nucleic acid bases. The equilibrium constant (2.54 ± 0.17 and 2.57 ± 0.29 I mol−1, calculated from the experimental data on purine and 6‐methylpurine, respectively) suggests the dominant role of the methylated counterpart in the association. The upfield dimer shifts indicate that the methyl group perturbs the plane‐to‐plane or stacking‐like arrangement in the associated state.
1H and 13C NMR studies of new polyamide–imides containing fluorene units
Authors: Jahnke Tamera S. , Mohite Sanjiv S.
Published: May 2005

1H and 13C chemical shifts are reported for a series of new polyamide‐imides prepared from an aromatic diamine and four acid dichlorides.
Attenuation of spin–spin effects in carbon‐13 T1ρ NMR experiments by multipulse proton homonuclear decoupling
Authors: Tekely Piotr , Canet Daniel , Delpuech Jean‐Jacques , Virlet Joseph
Published: May 2005

In crystalline polyoxymethylene, a system with tightly coupled protons, it is shown experimentally that the averaging of the dipolar local field of protons by multipulse proton homonuclear decoupling leads to a decrease in the spin–spin contribution to the 13C rotating frame relaxation rate.
Cryogenic NMR: Spectrometer design for studies of matrix‐isolated materials
Authors: Espidel Joussef E. , Harris Robin K.
Published: May 2005

The construction of equipment capable of studying the 1H NMR of samples down to 26 K is described. The system includes a facility for obtaining matrix‐isolated compounds at cryogenic temperatures. Samples can be changed without removing the cryogenic equipment from the probe area. An NMR method of obtaining the true temperature at the sample is described. Illustrative spectra of both pure compounds and a matrix‐isolated system are provided.
NMR studies of the reorientational motions of cyclopentadienyl ligands in solid cis‐ and trans‐[(η5‐C5H5)2Fe2(CO)2(μ2‐CO)2]
Authors: Aime Silvio , Botta Mauro , Gobetto Roberto , Orlandi Alessandra
Published: May 2005

Chemical shift anisotropies and spin‐lattice relaxation times, T1, were determined for bridging and terminal carbonyls in c's and trans isomers of [(η5‐C5H5)2Fe2(CO) 2(μ2‐CO)2]. The relaxation path of the 13CO resonances occurs through the dipolar interaction with the cyclopentadienyl protons modulated by the reorientational motion of the C5H5 (Cp) rings around their five‐fold axes. Wide‐line proton spin‐lattice relaxation times, T1, at variable temperature allow the evaluation of the activation energies associated with the internal rotation of the cyclopentadienyl rings. In the cis isomer, the two crystallographically non‐equivalent Cp ligands rotate at different rates (Ea = 7.2 and 15.8 kJ mol−1, respectively). Carbon‐13 spin‐lattice relaxation times in the rotating frame of the cyclopentadienyl carbons of the cis isomer support this view. Finally, good agreement is found between our work, the results obtained from crystallographic data and theoretical calculations on the energy barriers for the rotation of the Cp rings.
Multinuclear magnetic resonance study of Li2OSiO2 SolGel glasses
Authors: Dupree Raymond , Holland Diane , Mortuza Mohamed Golam , Smith Mark Edmund , Chen Aihu , James Peter F.
Published: May 2005

A multinuclear magnetic resonance study of some solgel prepared Li2OSiO2 glasses and of their crystallization is presented. The glasses, all of which have been heated to 400°C, are found to contain a large amount (ca. 20 mol‐%) of H2O, mostly in the form of OH. The local structure is very different from melt‐formed glasses in that the major modifier is H2O rather than Li2O, with the formation of Si(OSi)3OH units. The glasses start to crystallize at a lower temperature than melt‐formed glasses, with the first crystalline product being lithium metasilicate even for very silica rich sol‐gel compositions.
A pulse sequence for the measurement of short spin‐lattice relaxation times for carbon‐13 in solid polymers
Authors: Findlay Anita , Harris Robin K.
Published: May 2005

A pulse sequence is presented which allows measurement of short T1 values (< 1 s) in solids, avoiding probe damage by the use of saturating sequences of 90° pulses. The use of the sequence is illustrated for a cross‐linked polymeric system which contains composite peaks having both short‐T1 and long‐T1 components.
Complete proton and carbon spectral assignments of acrihellin and hellebrigenin
Authors: Müller Arndt , Nonnenmacher Gerhard , Kutscher Bernhard , Engel Jürgen
Published: May 2005

The complete assignment of all 1H and 13C NMR signals of acrihellin in chloroform solution is presented. The analysis of the 1H and 13C NMR spectra was performed using the heteronuclear 2D NMR techniques H,C‐COSY and H,C‐COLOC. For an unambiguous assignment of the 13C NMR spectrum the elucidation of carbon–carbon connectivities via 2D‐INADEQUATE was most important. The INADEQUATE experiment was also applied to hellebrigenin in DMSO‐d6 solution. This experiment confirmed a recently published carbon assignment.
Assignment of quaternary carbon resonances in lambertellin by soft heteronuclear multiple bond correlation
Authors: Keniry Max A. , Poulton Gerald A.
Published: May 2005

A one‐dimensional version of the heteronuclear multiple bond correlation experiment (HMBC) is shown to be an excellent alternative to the full two‐dimensional experiment when the carbon resonances are well resolved. The quaternary resonances of lambertellin, a metabolite of Ciboria gordonii Funk, are correlated to the previously assigned proton resonances by selective transfer of zero and double quantum coherence to observable proton magnetization by a frequency‐selective carbon decoupler pulse.