bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐resolution 13C NMR study of free and metal‐complexed ionophores in the solid state: Conformation and dynamics of the macrocyclic ring and the effect of intermolecular short contact of methyl groups on spin–lattice relaxation times and displacements of chemical shifts
Authors: Saitô Hazime , Tabeta Ryoko , Yokoi Motoko
Published: May 2005

High‐resolution 13C NMR spectra of 15 samples of uncomplexed and metal‐complexed tetranactin and nonactin were recorded in the solid state, revealing characteristic displacements of peaks due to complex formation and the effect of crystalline packing on the 13C chemical shifts and spin–lattice relaxation times of the methyl groups. The C‐1 13C chemical shifts of uncomplexed and complexed tetranaction and nonactin are well related to the variation of nearby torsion angles characteristic of the macrocyclic conformation, as determined by x‐ray diffraction. The existence of short intermolecular contact of methyl groups (<3.8 Å) at the surface of the molecules results in either prolonged 13C spin–lattice relaxation times in the laboratory frame (T1C) or substantial upfield displacement of peaks (up to 6 ppm). In addition, significantly reduced T1C values in uncomplexed nonactin (one order of magnitude smaller than those of other compounds) was ascribed to the presence of a puckering motion of the tetrahydrofuran ring and fluctuation of the macrocyclic ring in the solid state (with a time scale of 10−8 s). Finally, how the conformations of these compounds in the solid are retained in chloroform solution was examined in view of the differences in the 13C chemical shifts between the solid and solution.
EPR spectrum of the ion pair [CR(CO)5−]2 in irradiated crystals of PPh4+ HCr(CO)5−
Authors: Morton J. R. , Preston K. F. , Darensbourg M. Y.
Published: May 2005

UV‐irradiated crystals of PPh4+HCr(CO)5− exhibit anisotropic EPR spectra at room temperature and below which are characteristic of the presence of an electronic triplet (S = 1). From measurements of the angular dependence of the spectrum it is established that the carrier has axial symmetry with g‖ = 2.0019, g⟂ = 2.0202, |D| = 163.0 MHz, and with the unique direction parallel to the c axis of the tetragonal (P4/n) crystal. The magnitudes of the zero‐field parameter D and the g‐tensor components show that the carrier is a biradical consisting of a pair of Cr(CO)5− radicals separated approximately by one unit cell length along c. A weak single‐line spectrum which accompanies the triplet spectrum has the identical g‐tensor, and is assigned to the Cr(CO)5− radical itself. A third spectrum with the same g‐tensor, which is present in γ‐irradiated crystals only, is ascribed to another electronic triplet with |D| = 84 and E ≈︁ 0 MHz. It is associated with a second pair of exchange‐coupled Cr(CO)5− radicals whose interionic axis lies skew in the crystal axis system. Measurements of the signal intensities as a function of temperature show that both biradicals have singlet ground states and small isotropic exchange parameters, J ≈︁ 35 and 11 cm−1, respectively.
The NMR spectra of the porphyrins. 36—Ring currents in octaethylporphyrin, meso‐tetraphenylporphyrin and phthalocyanine complexes
Authors: Abraham Raymond J. , Medforth Craig J.
Published: May 2005

The change in ring current of octaethylporphyrin, meso‐tetraphenylporphyrin and phthalocyanine cobalt(III) complexes with axial amine ligands was studied using a double dipole network model. The porphyrin ring current was found to be highest in octaethylporphyrin but decreased by 5% in meso‐tetraphenylporphyrin and 29% in phthalocyanine. The ring current in the fused benzene rings of phthalocyanine was similar to that found in free benzene. An attempt was made to rationalize changes in the porphyrin ring current in terms of the porphyrin substituents.

An existing ring current program, DIPCALC, was modified to allow the calculation of ring current shifts for phthalocyanines. The parameters required to calculate ring current shifts for all three porphyrins are presented.
New approaches to oligosaccharide sequencing and conformational distribution around the glycosidic bond. One‐ and two‐dimensional 13C{1H} NOE spectroscopy
Authors: Batta Gy. , Kövér K. E.
Published: May 2005

Both negative, indirect heteronuclear NOE and 2D 1H13C relayed incoherent transfer spectroscopy are shown to be useful in oligosaccharide sequencing. The one‐ and two‐dimensional manifestation of the former effect allows the experimental determination of the average carbon–proton distances along the non‐rigid glycosidic bond. However, these preliminary attempts must be further improved for predicting the accurate weights of the preferred conformers.
Analysis of multiplets in two‐dimensional NMR spectra by topological classification: Applications to vinblastine and cyclosporin A
Authors: Pfändler Peter , Bodenhausen Geoffrey
Published: May 2005

A recently develpoed approach for the analysis of cross‐peak multiplets has been applied to two‐dimensional correlation spectra of the binary alkaloid vinblastine and the cyclic undecapeptide cyclosporin A. The experimental multiplet patterns are encoded in a manner that depends on the topology of the coupling network but not on the values of the coupling constants. Multiplets that are expected to occur for various possible coupling networks are similarly encoded in a library to allow comparison with experimental multiplets. The program is called MARCO POLO (Multiplet Analysis by Reduction of Cross peaks and Ordering of Patterns in an Overdetermined Library Organization). The outcome of this type of automated analysis is discussed in detail, with particular emphasis on remaining ambiguities.
Structure elucidation of a spirostanol glycoside from Asparagus officinalis fruits by concerted use of two‐dimensional NMR techniques
Authors: Pant G. , Panwar M. S. , Negi D. S. , Rawat M. S. M. , Morris Gareth A. , Thompson R. I. G.
Published: May 2005

Complete 13C and 1H assignments for the oligosaccharide segment of a novel spirostanol glycoside were derived, and structural proof obtained, using a combination of DEPT, heteronuclear chemical shift correlation, homonuclear relayed coherence transfer, absolute value COSY, phase‐sensitive double quantum filtered COSY, NOESY, INEPT and proton‐detected long‐range heteronuclear shift correlation via multiple quantum coherence.
cis–trans Isomerism in monoalkylhydroxamic acids by 1H, 13C and 15N NMR spectroscopy
Authors: Brown David A. , Glass William K. , Mageswaran Rajeswary , Girmay Berhane
Published: May 2005

The first example of cis–trans isomerism in monoalkylhydroxamic acids, detected by 1H, 13C and 15N NMR spectroscopy, is reported. The 15N NMR spectrum of CH3CO15NHOH gave a clear assignment of the OH and NH protons of both Z and E isomers. The assignment was confirmed by 1H and 13C NMR spectroscopy. A rotational barrier of isomerization (ΔGc≠) of 17.8 kcal mol−1 was calculated from the variable‐temperature 1H NMR spectra using the method of Shanan‐Atidi and Bar‐Eli.
Use of two‐dimensional NMR to assign the protons and carbons in cephalotaxine
Authors: Cheng Jin‐Long , Cui Yu‐Xin , Li Yu , Pan Xin‐Fu
Published: May 2005

Prton and 13C chemical shift assignments have been made for naturally occurring cephalotaxine. The assignments of two carbons are reversed from those in the liteature. The chemical shifts and configurations of the pyrrolidine protons, aminomethylene protons and benzylic protons in cephalotaxine have been determined by the application of several 2D NMR techniques.
Conformation and dynamics of ranitidine in solution as detected by 1H and 13C NMR spectroscopy
Authors: Gaggelli Elena , Marchettini Nadia , Sega Alessandro , Valensin Gianni
Published: May 2005

Conformational and dynamic features of ranitidine were delineated by 1H and 13C NMR 1D and 2D spectroscopy. Spin–lattice relaxation rates and homo‐ and hetero‐nuclear NOEs were measured. An extended conformation was shown to predominate in solution, with restricted segmental motion. The main reorientational motion and some of the internal motions were characterized in terms of stochastic internal motion around a molecular axis that reorients isotropically. Selective irradiation methods were used to obtain relevant conformational parameters.
Natural abundance carbon‐13 and deuterium NMR studies on the liquid and solid phases oftert‐butyl chloride andtert‐butyl nitrate
Authors: Aksnes D. W. , Ramstad K. , Bjørlykke O. P.
Published: May 2005

NMR line widths (13C) and spin–lattice relaxation times (13C and2H) were measured over a wide temperature region in liquid and solidtert‐butyl chloride (1) andtert‐butyl nitrate (2). Molecular self‐diffusion, with activation energies in the range 29–37 kJ mol−1, is responsible for the considerable line narrowing observed for the13C resonances in solid I of these substances.

An analysis of the13C and2H spin–lattice relaxation times (T1) in the liquid and solid phases of 1 and 2 is reported. Rotational correlation times, activation energies and pre‐exponential factors for the appropriate motions were obtained from the Arrhenius equation. The13C and2HT1data suggest that the overall reorientation occurring in solid I of 1 and 2 is slightly retarded by the melting process. The13CT1data show that the faster motion in the ordered phases of 1 and 2 is the uniaxialC3′ reorientation with an activation energy of 12–14 kJ mol−1, while the slower motion is theC3methyl reorientation with an activation energy of 12–13 kJ mol−1.
Correlation of carbon‐13 substituent‐induced chemical shifts revisited: Meta‐ and para‐substituted benzonitriles
Authors: Exner Otto , Buděšínský Miloš
Published: May 2005

Carbon‐13 NMR spectra are reported for 63 substituted benzonitriles in deuteriochloroform or in its mixture with dimethyl sulphoxide‐d6. The substituent‐induced chemical shifts (SCS) of the CN carbon correlate well with dual substituent parameters (DSP) in the para series but poorly in the meta series, whichever parameters are used. The DSP treatment was found to be inferior to principal component analysis (PCA), using as a probe 29 sets of literature data on α,β‐unsaturated benzene derivatives. Whereas one component is sufficient for meta derivatives, two terms are needed for para derivatives, which are different for the α‐ and β‐positions. The constants derived by PCA could be in principle used to predict further SCS, but their scope must be still explored.
Conformational analysis via vicinal carbon–hydrogen coupling
Authors: Waterhouse Andrew L.
Published: May 2005

The fully coupled (FUCOUP) correlation experiment was used to analyze conformation and stereochemistry on two dissimilar compounds, strychnine and camphor. This experiment detects the vicinal coupling between hydrogens and carbons, and the magnitude of this coupling is appraised by the presence or absence of cross‐peaks in the spectrum. This correlates with a first‐order approximation of the Karplus torsional angle relationship, although angles near 45° and 135° are not useful. The FUCOUP experiment works better than other related methods because it has no delays that modify the signal intensity of the coupling.
Investigation of the behaviour of propylene oxide in water by 1H NMR measurements
Authors: Xue Yi , Du You‐ru
Published: May 2005

As an electron donor solvent, propylene oxide (PO) forms a hydrogen bond with water in their binary mixture. The repulsion produced by the electrostatic field from the PO…HOH hydrogen bond forces the protons and methyl group of PO to bend away from the O group and results in the approach of these protons into the plane of the three‐membered ring. Consequently, they experience a stronger paramagnetic field from the ring current and their 1H resonances shift to a lower field. The changes of the HCH angle and HCCH dihedral angles of PO in water cause the geminal coupling constant and the vicinal cis coupling constant to decrease and the vicinal trans coupling constant to increase.
45Sc NMR study of scandium complex formation in non‐aqueous solutions
Authors: Kirakosyan G. A. , Tarasov V. P. , Buslaev Yu. A.
Published: May 2005

45Sc NMR parameters of isomeric ScIIIhexacoordinated complexes ScCl6−nLnn−3formed by the interaction of ScCl3with donor monodentate molecules of trimethyl phosphate, dimethyl sulphoxide, dimethylformamide, dimethylacetamide, formamide, tetramethylurea and Ph3PO in non‐aqueous solutions of CH3CN, CH3NO2, (CH3)2CO, CH3C(O)OC2H5, C4H8O and (C2H5)2O are reported.cis‐ScCl3(TMP)3has been shown to be the preferred species in solvents of low polarity. Increasing polarity of the medium leads to an increase in the relative concentration oftrans‐ScCl3(TMP)3, which has been explained in terms of the different solvation ofcisandtransmolecules owing to the difference in their polarity. The range of45Sc NMR chemical shifts in scandium complexes coversca340 ppm.
Zwitterionic piroxicam in polar solution
Authors: Geckle J. M. , Rescek D. M. , Whipple Earl B.
Published: May 2005

The selective broadening of 13C NMR lines in solutions of piroxicam in polar solvents is related to the equilibrium with its zwitterion by reference to the CP/MAS spectra of the known crystalline solids. The amount of zwitterion in N,N‐dimethylformamide solution at 205 K., in which the interconversion is slow enough to allow the separate spectra to be assigned, is 19%.
Conjugation of the cyclopropyl group
Authors: Galli Carlo
Published: May 2005

The capacities for the conjugation of a cyclopropyl group and of a double bond toward an unsaturated system were compared by 13C and 1H NMR.
1H and 13C NMR spectra and rotational isomerism of 1,3‐dibromobutane
Authors: Aksnes Dagfinn W.
Published: May 2005

The 1H and 13C NMR spectra of 1,3‐dibromobutane were assigned using selective proton decoupling 1D and selective proton‐flip 2D experiments. The chemical shifts and spin‐spin coupling constants were obtained from complete spectral analysis of the experimental 1H and 13C spectra. The spectral parameters obtained are discussed in terms of conformational and stereospecific substituent effects. The rotamer populations were obtained from the vicinal coupling constants, and the rotamers in which the CH3 and CH2Br groups are situated trans to each other contribute as much as 69% of the staggered forms.
Intramolecular non‐bonded interactions and 13C NMR chemical shifts
Authors: Pachter Ruth , Wessels Philippus L.
Published: May 2005

The recently proposed empirical analysis of β‐ and γ‐SCS in terms of the local non‐bonded van der Waals and electrostatic intramolecular interaction energies is extended to an application for the 13C NMR chemical shifts (δ) of primary, secondary and tertiary carbon atoms of numerous classes of unsubstituted hydrocarbons of varied degrees of strain. A correspondence is established between the (Evdw)M local non‐bonded interactions of tertiary carbon atoms and the theoretically evaluated Op shielding constants, and also between δ(13C‐prim); δ(13C‐sec) and the non‐bonded part of the molecular potential which describes binding energies in ESCA. In addition, it is shown that the δ(13C) values of primary, secondary or tertiary carbon atoms at positions β and γ to an OH substituent, in a variety of mono‐ and di‐hydroxy aliphatic molecules, are related to the local Evdw and Echarge interaction energies.
Aluminum‐27 nuclear magnetic resonance studies of ferron—hydroxo—polynuclear Al interactions
Authors: Bertsch Paul M. , Anderson Michael A. , Layton W. John
Published: May 2005

The [AIO4AI12(OH)24+n(H2O)12−n]7−n+(AI13) polynuclear species was found to interact with the commonly employed complexation agent ferron (8‐hydroxy‐7‐iodo‐5‐quinoline‐sulfonic acid) according to multiple reaction pathways. After the addition of ferron to the partially neutralized Al solution, a large portion of the Al13polymer was no longer observed by27Al NMR spectroscopy. The data indicated that the observed initial loss in Al13concentration resulted from precipitation with acetate (OAc) in the buffer, since the loss was not related to the ferron: Al molar ratio, because no corresponding increase in the Al‐ferron (δ = 3.4 ppm) resonance was observed and also because similar losses were noted in solutions where only NaOAc was added. The Al13remaining in solution was characterized by a resonance with an identical chemical shift (δ = 62.5 ppm), yet having wider line widths at half‐maximum (v1/2) than normally associated with the Al13polynuclear species. This suggested that the ferron is complexing with octahedrally coordinated Al comprising the cage‐like structure, and thus distorting the symmetry of the centrally located tetrahedral Al. The Al13—OAc solid phase was also being degraded by ferron more slowly, as indicated by the quantitatively larger increase in the ferron‐Al resonance than could be accounted for by the subsequent disappearance of the Al13peak. That a single polynuclear, the Al13, reacts with ferron via multiple reaction pathways helps to explain disparate interpretations in the literature based on indirect timed spectrophotometric assays regarding the existence of a large number of Al polynuclear structures.
Total assignment of the 1H and 13C NMR spectra of phenanthro[9,10‐b]thiophene: Concerted use of two‐dimensional NMR techniques
Authors: Johnston Milton D. , Salazar Miguel , Sims Larry D. , Zektzer Andrew S. , Castle Raymond N. , Martin Gary E.
Published: May 2005

The 1H and 13C NMR spectra of phenanthro[9,10‐b]thiophene were totally assigned using a combination of twodimensional NMR techniques. Direct hetcronuclear correlations were established using heteronuclear chemical shift correlation with semi‐selective proton decoupling. Two methods were employed to establish the identity of vicinal neighboring protons: heteronuclear relayed coherence transfer and low‐pass J‐filtered heteronuclear relayed coherence transfer. The versatilities of the two techniques were compared. Quaternary carbon resonance assignments and the orientations of individual spin systems relative to one another were accomplished using the proton‐detected long‐range heteronuclear multiple quantum coherence experiment (HMBC). Key long‐range inter‐ring proton homonuclear spin couplings served to confirm the orientations of the proton spin systems.
Substituent effects in cycloheptatrienyl radicals: An ESR spectroscopic study
Authors: Sustmann Reiner , Brandes Dieter , Lange Fritz , Tashtoush Hasan I.
Published: May 2005

ESR spectral parameters of methoxy‐, hydroxy‐ and cyano‐substituted cycloheptatrienyl radicals are reported. The radicals were obtained in adamantane matrices by the rearrangement of substituted bicyclo[3.2.0]heptadienyl radicals. The hyperfine splitting parameters are interpreted in terms of the effect of donor and acceptor substituents on the degeneracy of the relevant singly occupied ψs or ψA ABMO of the cycloheptatrienyl radical. In addition, an attempt was made to study the deuterium isotope effect on the degenerate MOs at low temperatures in a [2H16]adamantane matrix.
71Ga nuclear magnetic resonance investigation of aqueous gallium(III) and its hydrolysis
Authors: Akitt J. W. , Kettle David
Published: May 2005

The 71Ga resonance line width of the aquagallium cation [Ga(H2O)6]3+ is shown to vary with pH, and to have a minimum value of 53 Hz in the presence of excess acid and provided that the gallium concentration is not greater than 22 mM. It is shown that the dependence of line width on pH is due to self‐hydrolysis of the cation and is consistent with the known value of the 1,1 hydrolysis constant of pK1,1 = 2.6.
Effects of solute–solvent interactions on the nitrogen nuclear shieldings of some alkyl cyanides
Authors: Witanowski M. , Sicinska W. , Webb G. A.
Published: May 2005

It was found that the range of solvent effects on the nitrogen NMR shielding of the cyano group appears to be almost independent of the nature of the attached alkyl group and to be in excess of 20 ppm. Effects due to both the polarity of the medium and hydrogen bonding are observed to contribute almost equally to the nitrogen shielding ranges measured for four alkyl cyanides. These contributions are determined from the shielding in nitrogen variations with the solvent by means of a four‐parameter model and are supported by molecular orbital calculations employing the solvaton description of non‐specific solute‐solvent interactions. The observed responses of the nitrogen shieldings to solvent effect are found to be significantly different from those reported for sp2‐type nitrogen atoms.
1H and 13C chemical shifts of some 1, 2‐Dithiole‐3‐thione derivatives
Authors: Vaccher Claude , Berthelot Pascal , Debaert Michel
Published: May 2005

The 1H and 13C NMR signals for some 1,2‐dithiole‐3‐thiones, their intermediates and derivatives have been assigned.
Relationship between protonproton NMR coupling constants and substituent electronegativities. V—Empirical substituent constants deduced from ethanes and propanes
Authors: Altona Cornelis , Ippel Johannes H. , Hoekzema Aldert J. A. Westra , Erkelens Cornelis , Groesbeek Michel , Donders Lambertus A.
Published: May 2005

The electronegativity dependence of the torsion angle‐independent term in the Karplus equation, i.e. of the ‘constant’ A in the Fourier expansion A + B cos ϕ + C cos 2ϕ +…, was investigated. Experimental proton‐proton coupling constants of substituted ethanes and isopropanes appeared to be suitable for this purpose. A data set was constructed which contained 70 couplings, newly measured or remeasured at 300 MHz, and 25 couplings taken from the literature. The accuracy of each data point is estimated as ≤0.02 Hz, with a few exceptions. The actual analysis was carried out on 93 data points, i.e. on J values of 55 mono‐ and of 38 1,1‐di‐substituted ethanes, including 22 isopropyl derivatives. A total of 55 chemical groups is represented in the set; some of these were taken together, leaving 50 distinct groups. Regression analysis of the present data versus standard electronegativities did not yield acceptable results. Instead, substituent parameters λe, valid for 3J(HH) in saturated HCCH fragments, were derived in a least‐squares procedure from the data set. The couplings from mono‐ and 1,1‐di‐substituted ethanes could be accounted for in a simple expression that contains an interaction term C012(λ1λ2). The best equation obtained is

The parameters are valid for λe values scaled according to the Huggins electronegativities: λH = 0, λOR = 1.40. The equation fits 84 experimental couplings with a root‐mean‐square deviation of 0.018 Hz and a maximum deviation of 0.06 Hz. Some exceptions occur. (i) CH3CH3, CH3CHCl2 and CH3CHF2 appear to follow a different, but correlated, regression; (ii) C(O)H, C(O)R, SO2Cl and POCl2 groups require different λe values according to the substitution pattern, i.e. mono‐ or 1,1‐di‐substitution. The striking difference between the new λe substituent‐effect scale and other empirical electronegativity scales lies in the inverse correlation of λe with increasing electronegativity of β‐substituents. The inverse relationship is not only found for α‐carbon atoms, but appears to represent a general phenomenon, also seen for substituted α‐hetero atoms (O, N, S).
Correlation of carbon‐13 substituent‐induced chemical shifts: Meta‐ and para‐substituted methyl benzoates
Authors: Buděšńský Miloš , Exner Otto
Published: May 2005

Carbon‐13 NMR spectra are reported for 69 substituted methyl benzoates in deuteriochloroform or in its mixture with dimethyl sulphoxide‐d6. The substituent‐induced chemical shifts (SCS) of the CO carbon correlate poorly with dual substituent parameters (DSP) in all possible modifications, and for meta derivatives in particular this correlation is both overpara meterized and imprecise. A much better correlation was obtained with parameters (designated Bm, Bp and Cp) derived previously by principal component analysis (PCA) from a larger set. The SCS of the CH3 carbon correlate very well with the original simple Hammett equation, and no DSP treatment is needed. The clustering of substituents is not consequential in such a large set.
Carbon‐phosphorus heteronuclear shift correlation via multiple quantum coherence
Authors: Sims Larry D. , Soltero Luis R. , Martin Gary E.
Published: May 2005

Heteronuclear carbon‐phosphorus chemical shift correlation via heteronuclear multiple quantum coherence is described. Enhanced sensitivity is afforded by inverse detection of 31P rather than the much less abundant 13C spin. Correlations via 1J(CP) and nJ(CP), where n = 2, 3, are observable with minor variation in the pulse sequence; a low‐pass J‐filter was employed in the case of the latter to aid in suppressing responses that would normally arise from 1J(CP) coupling pathways in the long‐range experiment.
Different solution and solid‐state conformations of the antibiotic cycloheximide
Authors: Perry Nigel B. , Blunt John W. , Munro Murray H. G.
Published: May 2005

The 1H NMR spectra of the antibiotic cycloheximide in CDCl3 and CD3OD have been assigned. Analyses of coupling constants and difference NOE spectra showed different conformations in these two solvents, due to changeover between intra‐ and inter‐molecular hydrogen bonding. The twist boat cyclohexanone found in the solid state was not detected in solution. The results are compared with the solution and solid‐state conformations of the antitumour agent sesbanimide A.
Effect of substituents on the 13C NMR chemical shifts of 2‐R‐3‐methylbenzothiazolium quaternary salts and 2‐R‐benzothiazoles
Authors: Solčániová Eva , Čulák Igor
Published: May 2005

The 13C chemical shifts of 2‐R‐3‐methylbenzothiazolium quaternary salts and the corresponding 2‐R‐benzothiazoles are presented.
Proton and carbon NMR spectra of 2‐substituted dibenzothiophenes
Authors: Jayalakshmi S. , Perumal S. , Wilson D. A.
Published: May 2005

The proton and carbon NMR spectra of six 2‐substituted dibenzothiophenes are reported. Their analysis, mainly by correlation with benzene substituent‐induced chemical shifts, allows the correction of carbon shift assignments for a further five such compounds previously reported.
Unprecedented example of a 3J(13C,11B) through a CCNB linkage
Authors: Atchekzaï Jean , Bonnetot Bernard , Duplan Jean‐Claude , Fenet Bernard , Ferage Bernard , Mongeot Henri
Published: May 2005

The 13C NMR spectra of the tertiary amine‐boron trihalide adducts C6H5CH2N(CH3)2BX3 (X = Cl, Br, I) (I) and (C2H5)3NBCI, (2) show a long‐range 3J(13C,11B) coupling which was observed as an asymmetric quartet and measured as 2.2, 2.3 and 2.3 Hz for 1 (X = Cl, Br, I) and 1.1 Hz for 2.
Dynamic NMR study of the electronic state of heteroaromatics. V—Influence of the counter anion, ortho substituents and the ring heteroatom on the exocyclic C,N rotational barrier of pyrylium and thiopyrylium salts
Authors: Kleinpeter E. , Spitzner R. , Schroth W.
Published: May 2005

The 13C NMR spectra and variable‐temperature 1H NMR spectra of some NR2‐substituted pyrylium and thiopyrylium salts were studied, and the rotational barriers thus obtained about the exocyclic partial CN double bonds are discussed according to their dependence on the counter anion and other structural variations. The counter anion has a negligible influence on the barrier, but substituents on the ring can either strengthen electronically or weaken sterically the mesomerism of the NR2‐heteroaromatic system. The competition between these two effects is readily estimated from the rotational barriers obtained. The pyrylium salts display higher rotational barriers than the identically substituted thiopyrylium salts.
Determination of the pyrrolizidine alkaloids from Senecio jacobaea by 1H and 13C NMR spectroscopy
Authors: Pieters Luc A. C. , Van Zoelen Agnes M. , Vrieling Klaas , Vlietinck Arnold J.
Published: May 2005

A method for the determination of the pyrrolizidine alkaloids from Senecio jacobaea (Compositae) by 1H and 13C NMR is presented. 1H NMR is a reliable method for the determination of the total alkaloid level. 13C NMR appears to be a suitable method for the determination of the individual alkaloids. The same techniques can also be applied to other plants containing pyrrolizidine alkaloids.
Revised assignments of the 13C NMR spectra of some hydrophenanthrenes
Authors: Ernst Ludger , Stolle Ralf
Published: May 2005

13C and 1H NMR chemical shift assignments are reported for five hydrophenanthrene derivatives. Erroneous literature assignments have been corrected.
ESR evidence for the stereospecific spin trapping of 5‐alkyl‐5‐methyl‐1‐pyrroline N‐oxides
Authors: Zhang Yongkang , Xu Guangzhi
Published: May 2005

The ability of ten cyclic nitrones, 5‐alkyl‐5‐methyl‐1‐pyrroline N‐oxides, to trap a variety of short‐lived free radicals has been investigated using ESR spectroscopy. Stereospecific spin trapping by these nitrones has been demonstrated by comparison of the ESR spectra of their adducts with the ESR spectra of the corresponding 5‐alkyl‐5‐methyl‐1‐tetrahydropyrrolyl‐1‐oxyls. Phenyl radical trans addition to these nitrones has also been proved.
13C NMR of coumarins. III—Simple coumarins
Authors: Macias F. A. , Massanet G. M. , Rodríguez‐Luis F. , Salvá J.
Published: May 2005

13C NMR data for several simple coumarins are reported. The γsyn effect of a 5‐methoxy substituent on the C‐4 chemical shift was observed and measured. The effects of an 8‐iodo substituent on the chemical shifts of the carbons of the coumarinic skeleton are discussed.
13C relaxation in cyclopentadienyliron dicarbonyl acyl compounds
Authors: Nance Lewis E. , Will H. J. , MacQueen D. Brent , Garrison J. Mark , Nicklaw Jeffrey M.
Published: May 2005

T1 values for the protonated carbons of four acyl compounds, all possible combinations of methylpropanoyl and 2‐ethylbutanoyl groups with cyclopentadienyl‐ and methylcyclopentadienyl‐iron dicarbonyl, were determined at ambient temperature. Carbon‐13 T1 ratios for the acyl group relative to the ring system indicate relative differences in motion when obtained in the two solvents, CDCl3 and CD2Cl2. T1 values at −10°C, relative to 24°C, give further insight into motional modes. Carbon‐13 and proton NMR chemical shift values for all compounds and the NOE for one compound are reported.
Relationships between 1H, 13C and 17O NMR chemical shifts and H/D isotope effects on 13C and 17O nuclear shielding in intramolecular hydrogen‐bonded systems
Authors: Liepiņš E. , Petrova M. V. , Gudriniece E. , Pauliņš J. , Kuznetsov S. L.
Published: May 2005

The intramolecular Hbond strength in cis‐enolic forms of β‐diketones was investigated. The correlations between the 1H hydroxyl proton shieldings and the chemical shifts of the 13C and 17O nuclei involved in the chelate ring, and the H/D isotope shifts on the latter resonances, were determined. An increase in the hydrogen bond strength leads to increasing values of H/D isotopic shifts on the 17O resonances. The results obtained are compared with quantum chemical calculations and x‐ray measurements.
Dynamic nuclear magnetic resonance study of intramolecular processes in cyclohexanediaminetetraacetate–metal complexes
Authors: Ba Yong , Song Rui‐Fang , Qiu Zu‐Wen
Published: May 2005

The dynamic NMR (DNMR) of the intramolecular acetate scramblings that occur in Ca(II)‐, Sr(II)–, Ba(II)– and La(III)–cyclohexanediaminetetraacetate complexes has been studied. The working temperature range was extended to 430 K by using a sealed thick‐walled capillary sample tube and new DNMR phenomena were thus observed. Information on activation energy, enthalpy, entropy and the free energy of nitrogen inversion of the chelates was obtained by computer analysis.
Assignment of the 1H, 13C and 15N NMR spectra of methyl β‐D‐glucopyranoside tetranitrate, β‐cellobiose octanitrate and cellulose trinitrate by two‐dimensional homonuclear and heteronuclear 13C1H and 15NOC1H shift correlation spectroscopy
Authors: Axenrod T. , Liang B. , Bulusu S.
Published: May 2005

The unambiguous assignment of all the 1H, 13C and 15N resonance signals in methyl β‐D‐glucopyranoside tetra‐nitrate and β‐cellobiose octanitrate was made using homonuclear and heteronuclear 13C1H and 15NOC1H two‐dimensional shift correlation NMR experiments. Solvent‐induced shifts were used to confirm the 13C1H correlations in β‐cellobiose octanitrate. Based on these observations and selective decoupling experiments, the 15N resonance signals in cellulose trinitrate were tentatively assigned.
NMR study of three heteroyohimbine derivatives from Rauwolfia serpentina: Stereochemical aspects of the two isomers of reserpiline hydrochloride
Authors: De Bruyn André , Zhang Weiguo , Buděšinský Miloš
Published: May 2005

1H NMR data for isoreserpiline and tetraphylline and 1H and 13C NMR data for reserpiline hydrochloride are presented. New insights into the 1H NMR coupling constants of the heteroyohimibines provide an easy means of assigning their configuration and conformation, allowing the elucidation of the stereochemical features of the two isomers of reserpiline hydrochloride.
Preparation and structure of cycloalkane‐condensed [1,3]thiazino[3,2‐a] pyrimidinones
Authors: Sohár Pál , Szöke‐Molnár Zsolt , Stájer Géza , Bernáth Gábor
Published: May 2005

Isocyanate salts prepared from cis‐2‐amino‐1‐cyclopentane‐ and ‐hexane‐carboxylate and the corresponding trans‐cyclohexane and ‐cyclohexene derivates with KSCN were cyclized to cycloalkane/ene‐condensed 2‐thioxo‐4‐pyrimidinones, which were transformed to tricyclic 1,3‐thiazino[3,2‐a]pyrimidinones by addition of dimethyl acetylenedicarboxylate. The stereo structures of the new compounds were established by IR and 1H and 13C NMR spectroscopy, making use of the signal multiplicities in the proton‐coupled carbon spectra.
13C NMR studies of tautomerism in imidazo[4,5‐c]pyridines
Authors: Barraclough P. , Lindon J. C. , Nobbs M. S. , Williams J. M.
Published: May 2005

A detailed analysis of the 13C NMR spectra of the 1‐N‐ and 3‐N‐methyl derivatives of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine, utilizing long‐range couplings and 2D 1H13C correlation experiments, has led to an unambiguous assignment of all carbons. Comparison of these definitive assignments of C‐3a and C‐7a, in particular, with those of the tautomers of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine has permitted confirmation of the predominance of the 1H‐tautomer for the latter. In addition, previous conflicting assignments for 1H‐imidazo[4,5‐c]pyridine and its 3‐N‐methyl derivative are now resolved. Revision of these assignments leads to the conclusion that the 1H‐tautomer of 1H‐imidazo[4,5‐c]pyridine is predominant.
1H and 13C NMR assignments for lanostan‐3β‐ol derivatives: Revised assignments for lanosterol
Authors: Emmons Gary T. , Wilson William K. , Schroepfer Jr George J.
Published: May 2005

1H and 13C NMR assignments are presented for 30 oxygenated lanostane derivatives, including lanosterol, dihy‐drolanosterol, 7‐ketolanosterol, agnosterol, 24,25‐epoxylanosterol, 8α,9α‐epoxylanostan‐3β‐ol, three 15‐oxygenated derivatives of lanost‐7‐en‐3β‐ol, lanostane‐3β,7α‐diol, lanostane‐3β,9α‐diol and their acetates. These assignments, which were largely determined by a combination of DEPT, one‐boad and long‐range 13C1H chemical shift correlation and lanthanide‐induced shift experiments, are not dependent on previously reported assignments, several of which were found to be incorrect. 1H and 13C acetylation shifts for lanostan‐3β‐ols were sufficiently invariant among the sterols studied that they were useful for assigning carbons in rings A and B. The acetylation shifts reported for lanostan‐3β‐ols were extended and partially revised.
Solvent effect on the 13C and 15N NMR chemical shifts and rotational barriers in N,1N1‐dimethyl‐and N,1N1‐hexamethylene‐N2 ‐phenylformamidines
Authors: Wawer Iwona
Published: May 2005

Solvent‐induced 13C NMR chemical shifts of N1,N1‐dimethyl‐N2‐phenylformamidine can be correlated with the acceptor number of solvents, AN, and also with the π* and α parameters of Kamlet and Taft. No correlation was found for the height of the rotational barrier around the CN1 bond. The self‐association of formamidine and the influence of polar, aprotic solvents cause an increase in ΔG1 of approximately 1 kJ mol−1 whereas, contrary to expectations, the ΔG1 values found in hydrogen‐bonding solvents are smaller than in cyclohexane. The barrier, however, increases with the strength of the hydrogen bond and on protonation. Downfield shifts of the N1 and upfield shifts of the N2 signals were observed in the 15N NMR spectra of formamidine when the strength of the hydrogen bond with the solvent increased.
Isotope effects on the 13C NMR chemical shifts of 5‐substituted indoles: Evidence for electron density dependence on the hydrogen (deuterium) atom
Authors: Morales‐Ríos M. S. , Del Río R. E. , Joseph‐Nathan P.
Published: May 2005

The dependence of the deuterium/hydrogen NMR isotope effects on 13C chemical shift (DHIECS) values on the electron density at the hydrogen (deuterium) atom in a series of para‐like substituted indoles with a partially deuterated NH site, measured as 0.83 M solutions in DMSO‐d6, is established on the basis of a series of correlations relating the isotope shifts with Hammett‐type í parameters, 1H(NH) chemical shifts, 15N chemical shifts and group electronegativity. The sensitivity of the nΔ isotope effects appears to be connected closely with electron redistribution at the 5‐substituent of the carbon atom under consideration.
13C NMR assignment of protonated carbons in d‐type porphyrins
Authors: Timkovich Russell , Bondoc Laureano L.
Published: May 2005

The 13C resonances for all protonated carbons have been observed and assigned for the free base esters derived from the following natural products: heme d, the prosthetic group of the bacterial cytochrome oxidase cytochrome d; heme d1, the prosthetic group of the dissimilatory nitrite reductase cytochrome cd1; and a stable form of sulfheme, the chemically modified prosthetic group from the degradation product of myoglobin known as sul‐fmyoglobin. These partially saturated porphyrins have in common that a heteroatom or atoms has added to a pyrrolic carbon. 13C NMR spectra were obtained on limited amounts of naturally derived samples by proton‐detected heteronuclear correlation spectroscopy.
Accuracy of molecular dynamics obtained by T1ρ measurements on the microsecond time scale in solution
Authors: Wang Yu‐Sen , Ikuta Satoshi
Published: May 2005

Measurements of T1ρ were performed for well characterized systems in which the number and population of exchange sites are known. These systems include the chair‐to‐chair isomerization of cyclohexane‐d11, a two‐site exchange model with equal population, and the cis‐trans isomerization of methyl nitrite, a general two‐site exchange model. The kinetic parameters obtained by T1ρ measurements were compared with other published results, and the predicted and observed chemical shift difference between the two sites at low temperature were more rigorously compared. These comparisons showed that measurements of T1ρ in solution provide a convenient probe of the molecular dynamics in solution on the microsecond time scale.
Use of an internal reference in 13C chemical shift measurements
Authors: de Kowalewski D. G. , de Los Santos C. , Marceca E.
Published: May 2005

The use of the nominal value of the chemical shift of the solvent to calibrate the spectrometer in 13C NMR spectroscopy was found to introduce errors due to the effect which the solute has on the solvent. In addition, hexamethyldisiloxane (HM) is proposed as an internal standard; owing to its high boiling point it is easier to manipulate than tetramethylsilane (TMS) and it is therefore possible to prepare solutions of known concentrations. In order to convert the data obtained with this standard to the TMS scale, the chemical shift of HM was determined in 16 solvents using cyclohexane as external standard in a spherical cell (5% w/w concentration of HM) as a function of the solvent factor g2. Comparing these results with a similar plot obtained previously for TMS by other workers, it is possible to convert one type of data to the other by a simple linear expression.
Side‐band analysis in variable‐angle sample‐spinning (VASS) NMR for the central transition of quadrupolar nuclei (half‐integer spin)
Authors: Amoureux J. P. , Fernandez C. , Lefebvre F.
Published: May 2005

Variable‐angle sample‐spinning (VASS) NMR was investigated for the case of limited rotation speed of the spinner. Side‐band intensities and line‐shapes for the central transition of half‐integer quadrupolar spin nuclei were calculated as a function of the parameter \documentclass{article}\pagestyle{empty}\begin{document}$ X = \frac{1}{4}[I(I + 1) - \frac{3}{4}]v_{\rm Q} ^2 (1 + \eta ^2 /3)/v_{\rm L} v_{\rm R}$\end{document}. It is shown that complex sideband patterns can be analysed using a very fast computational program.
13C relaxation and anisotropic molecular reorientation in liquid dibromomethane
Authors: Nance Lewis E. , Nealey Marty R. , Rodriguez A. A.
Published: May 2005

Although dibromomethane is a simple molecule, little work has been directed toward the analysis of its reorien‐tational motion. This is surprising, since two components of its inertia tensor are nearly degenerate and may, in principle, be treated as a quasi‐symmetric top. The 13C spin–lattice relaxation times and nuclear Overhauser enhancements were measured at various temperatures in the liquid phase. Field‐dependent measurements indicated the presence of the scalar relaxation mechanism. Calculated rotational diffusion constants were found to be in reasonable agreement with values predicted by the J‐diffusion model of inertially controlled reorientation. The results show that scalar coupling of the second kind is an important mechanism for 13C spin–lattice relaxation in this molecule. The data further indicates that dibromomethane may indeed be exhibiting quasi‐symmetric top behavior of this phase.
Method for evaluating the reliability of distances and rotational correlation times deduced from 2D 1H NMR NOESY experiments
Authors: Genest D. , Simorre J. P.
Published: May 2005

An experimental method is proposed which selects from all the inter‐proton distances r determined from two‐dimensional NMR NOESY experiments, those which do not depend on the internal motions of the molecule under investigation. Only these distances are quantitatively reliable for modelling purposes, owing to (1/r6) averaging and the possible correlation between r and the orientation of two protons as a consequence of the molecular Brownian internal dynamics. All the other distances must be used only qualitatively. Two examples of the application of this method to the lipopeptide stendomycin are given.
Carbon‐13 spin–lattice relaxation study on molecular dynamics of some penta‐ and tricarbonylchromium complexes
Authors: Gryff‐Keller Adam , Szczeciński Przemyslaw , Koziel Hanna
Published: May 2005

Carbon‐13 spin–lattice relaxation times were measured for some penta‐ and tricarbonylchromium complexes of organic ligands. The chemical shift anisotropy of the carbonyl carbons was estimated to be ca. 500 ppm. The contributions of dipole–dipole and chemical shift anisotropy mechanisms to the overall relaxation were evaluated and used to determine the reorientational parameters for the ligand and carbonylchromium moieties. It seems that the internal rotation rate about the ligand—chromium bond is governed mainly by intermolecular interactions.
Dynamics at the active site of N,N‐bis(2‐fluorophenyl)carbamoyl‐α‐chymotrypsin
Authors: Kairi M. , Gerig J. T.
Published: May 2005

N,N‐Bis(2‐fluorophenyl)carbamoyl chloride inactivates the serine protease α‐chymotrypsin by stoichiometric carbamoylation, presumably at the active site serine‐195 residue. At sample temperatures above 25°C fluorine NMR spectra of this enzyme derivative reveal the presence of conformations which are interchanged by processes that have ΔG of about 70 kJ mol−1 as estimated by two independent methods. Fluorine NMR spectra of the protein dissolved in 8 M urea were characterized by shift and relaxation parameters which suggest an unfolded state for the protein but with interconversion kinetics similar to those of the native structure. At sample temperatures below 25°C a second kinetic process becomes apparent in the spectra of both the native and denatured protein, although it was not possible to quantitate the rate of this process. These spectral changes are discussed in terms of the likely conformational properties of the N,N‐bis(2‐fluorophenyl) group attached to the native enzyme and are shown to be consistent with one of the 2‐fluorophenyl rings having a high barrier to rotation, and thus rotating slowly, while the other rotates rapidly. Both rings rotate rapidly in the denatured protein. A form of the modified enzyme which had fluorine NMR characteristics similar to those of the denatured enzyme yet was fairly soluble in 0.05 M sodium chloride solution was detected in samples after extended heating; formation of this species was not readily reversible. Spin‐lattice relaxation times (T1) and 19F{1H} NOE data for the native and denatured modified enzymes are reported.
Two‐path spin–spin coupling in tetrastannacyclohexanes
Authors: Mitchell Terence N. , Faust Rüdiger , Fabisch Bodo , Wickenkamp Roland
Published: May 2005

Tin‐119 NMR data are presented for thirteen 1,2,4,5‐tetrastannacyclohexanes. The one‐bond tin‐tin coupling constant shows a monotonic decrease with increasing methyl substitution at the ring carbon atoms. In a series of compounds the two‐path couplings 2+4J(SnSn) and 3+3J(SnSn) can be assigned and interpreted on the basis of a sign change for the former coupling. Values of 4J(SnSn) for substituted 2,3,5,6‐tetrastannaheptanes suggest that the magnitude of the four‐bond component of 2+4J(SnSn) in the stannacycles can be considerable.
Study of the self‐association of methylated pyrimidines in aqueous solutions by 1H NMR chemical shifts
Authors: Aradi Ferenc
Published: May 2005

The self‐association of pyrimidine and its methylated derivatives was studied by measuring the concentration‐dependent changes in proton chemical shifts in deuterium oxide at 35°C. The data were analysed by a dimer model with two parameters. The equilibrium constants give an increasing tendency for self‐association within the series pyrimidine (0.091 ° 0.006 l mol−1) < 5‐methylpyrimidine (0.165 ° 0.006 l mol−1) ≈ 4‐methylpyrimidine (0.183 ± 0.005 l mol−1) < 4,6‐dimethylpyrimidine (0.410 ± 0.011 l mol−1), and the values of the dimer shifts suggest a stacking‐like arrangement for the associated molecules.
13C NMR study on linderones and lucidones
Authors: Ng Soon , Lee Hiok‐Huang , Bennett Graham J.
Published: May 2005

The 13C NMR spectra of linderone (1), lucidone (2), methyllinderone (3), methyllucidone (4), demethyllinderone (7), dihydrolinderone (8) and 2‐(1‐hydroxyethylidene)‐4‐methylcyclopent‐4‐ene‐1,3‐dione (9) are reported. The 1H chemical shift data for 1–4 are also reported. Geometric isomers exist in 4, while external tautomers exist in all the other compounds (except 3) through strong intramolecular hydrogen bonding. With the aid of deuterium isotope effects (in 1 and 2), C‐H coupling constants and nuclear Overhauser effects, the 13C NMR spectra are assigned to the external tautomers and the geometric isomers.
Anthraquinone sulphonate as a general‐purpose shift reagent for the NMR analysis of cyclodextrins
Authors: Djedaïni Florence , Perly Bruno
Published: May 2005

The potential use of sodium anthraquinone 2‐sulphonate (ASANA) as a general‐purpose shift reagent for cyclodextrins is reported. It is demonstrated that completely resolved proton NMR spectra are obtained on inclusion of the host in the cavity of β‐and y‐cyclodextrins. The inclusion complexes have been characterized in terms of stoichiometry and association constants.
Nitrogen‐15 NMR, 2D NMR and ESCA characterization of a new stable 6a‐thia(SIV)‐1,6‐diazapentalene
Authors: Weber Lutz , Szargan Rüdiger , Schulze Bärbel , Mühlstädt Manfred
Published: May 2005

Reaction of 2‐methyl‐3‐thiocyanatocrotonaldehyde with aniline hydrochloride and subsequent addition of dicyclohexylamine afforded a new 6a‐thia(SIV)‐1,6‐diazapentalene. The presence of the NSN bond was verified through the N 1s and S 2p binding energies and the nitrogen‐nitrogen coupling constant in the doubly 15N‐labelled compound, prepared by using [15N]aniline hydrochloride.