bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractUV‐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

AbstractThe 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

AbstractBoth 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

AbstractA 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

AbstractComplete 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

AbstractThe 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

AbstractPrton 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

AbstractConformational 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

AbstractNMR 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

AbstractCarbon‐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

AbstractThe 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

AbstractAs 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

Abstract45Sc 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

AbstractThe 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%.
1H and 13C NMR spectra and rotational isomerism of 1,3‐dibromobutane
Authors: Aksnes Dagfinn W. 
Published: May 2005

AbstractThe 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

AbstractThe 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

AbstractThe [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

AbstractThe 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

AbstractESR 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

AbstractThe 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

AbstractIt 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.
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

AbstractThe 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

AbstractCarbon‐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

AbstractHeteronuclear 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.