bluuebunny/crossref_metadata_2025_split huggingface dataset:
A multinuclear NMR spectroscopic study of some Mo(CO)4[(R2″PO)2Si(R)R′] complexes [R2″=Ph2, OCH2CMe2CH2O; R, R′ = alkyl, haloalkyl, aryl]
Authors: Gray Gary M. , Redmill Keith A. 
Published: May 2005

AbstractIt is possible to use multinuclear NMR spectroscopy to measure both the steric and electron donor/acceptor properties of the P‐donor ligands in Mo(CO)4[(R2″PO)2YRR′] complexes [R2″=Ph2, OCH2CMe2CH2O; YR = P(O), Si(Me); R′ = alkyl, haloalkyl, aryl]. The 13C, 29Si, 31P and 95Mo NMR data for some Mo(CO)4[(R2″PO)2YRR′] complexes [R2″ = Ph2, OCH2CMe2CH2O; YR = P(O), Si(Me); R′ = alkyl, haloalkyl, aryl] are presented and the factors affecting both the chemical shifts and coupling constants are discussed. The linear correlations between the chemical shifts of the cis and trans CO 13C, the 29Si, the 31P and the 95Mo resonances of the R2″ = Ph2 complexes and those of the similar resonances of the R2″ = OCH2CMe2CH2O complexes are also discussed.Good linear correlations have previously been found between the differences in the 13C chemical shifts of the non‐equivalent cis CO, phenyl C‐1 and phenyl C‐2,6 resonances of a series of Mo(CO)4[(Ph2PO)2Si(Me)R′] complexes [R′ = Me, Et, n‐Pr, c‐Hex, t‐Bu and CH2Cl] and the Ea parameters of the R groups. It is now reported that the chemical shift differences of similar complexes with long‐chain alkyl and chloroalkyl R′ groups do not give good correlations with the Ea parameters. In addition, similar correlations are not observed when the Ph groups are replaced with an OCH2CMe2CH2O group. The factors which affect the poor correlations are discussed.
Cross‐polarization‐induced explosive decomposition of certain electrically conducting polymers
Authors: Axelson D. E. , Leung W. M. , Van Dyke J. D. 
Published: May 2005

AbstractThe cross‐polarization/dipolar decoupling‐induced explosive decomposition of certain electrochemically synthesized polymeric derivatives of thiophene and pyrrole is discussed. Suggested procedures for screening such potentially hazardous materials are presented.
Carbon‐13 NMR spectra of 1,3‐dioxolanes. I—new parameters for cis‐ and trans‐4‐methyl groups in 2,4‐disubstituted derivatives
Authors: Espinosa Antonio , Gallo Miguel A. , Campos Joaquín , Entrena Antonio , Camacho Encarnación 
Published: May 2005

AbstractThe 13C NMR spectra of 24 1,3‐dioxolane derivatives are reported in an attempt to propose parameters for the C‐2, C‐4 and C‐5 shifts from the 2‐Me and 4‐Me substituents, based on the ring stereochemistry. These parameters are obtained from simultaneous equations, and clearly agree with those calculated by the use of pattern molecules. The calculated parameter for the C‐4 shift due to a 2‐Me group differs notably from that proposed by other workers.
An EPR study of the thermal decomposition of molten 2,4,6‐trinitrotoluene and its isotopic analogs
Authors: Swanson Jon T. , Davis Larry P. , Dorey R. Cameron , Carper W. Robert 
Published: May 2005

AbstractElectron paramagnetic resonance spectroscopy has been used to probe the decomposition pathway of neat molten 2,4,6‐trinitrotoluene (TNT). The analogs of TNT labelled in the 2‐, 2,6‐, 4‐ and 2,4,6‐positions with 15N, and labelled in the α‐, 3,5‐ and α,3,5‐position with 2H have been studied, and their spectra recorded at 240°C. The results indicate that the earliest observable radical produces a spectrum resulting from coupling with a para‐N (aN = 10.8G), five equivalent hydrogens (aH = 2.7G) and two benzylic hydrogens (aH = 10.7G).
Natural abundance 15N chemical shifts in substituted benzamides and thiobenzamides
Authors: Brownlee R. T. C. , Sadek M. 
Published: May 2005

Abstract15N Substituent chemical shifts (measured at natural abundantc at 0.4 M concentration) and calculated (ab initio, STO‐3G) electron densities at the nitrogen and oxygen (or sulphur) are reported for series of para and meta‐substituted benzamides and thiobenzamides with NMe2, NH2, OMe, NHCOMe, F, Cl, Br, I, Me, H, COMe, COOMe, CF3, CN, NO2, CONH2 and CSNH2 substituents. The 15N shift are very sensitive to the substituent effects. The dual substituent parameter method shows excellent correlations of 15N shifts against substituent field and resonance effects, with the sensitivity in the thiobenzamides being double that in the benzamides. In contrast, calculated π‐electron densities at the nitrogen show the same sensitivity to substituents in both series. The 15N shifts correlate well with the calculated π‐electron densities at the nitrogen; however, estimates of the shielding based on local electron densities (described in Pople's independent electron model) cannot account for the increased sensitivity to the substituent effects observed for 15N chemical shifts of thiobenzamides. It is suggested that non‐local shielding from sulphur and oxygen are responsible for the chemical shift trends.
Microcomputer‐based 13C NMR spectral simulation of substituted alkanes
Authors: Hearmon R. Angus 
Published: May 2005

AbstractThe empirical prediction of 13C NMR chemical shifts using the Lindeman‐Adams rules and substituent chemical shift parameters is a useful aid for the chemist in the interpretation of spectra. The program Alkanes, written in Basic for a desk‐top microcomputer, automates the chemical shift estimation.
Investigation of prototropic equilibria by carbon‐13 relaxation time analysis
Authors: Elst L. Vander , Van Haverbeke Y. , Maquestiau A. , Muller R. N. 
Published: May 2005

AbstractQuaternary 13C dipole–dipole spin–lattice relaxation times are used to analyse prototropic equilibria of 2‐acetylbenzimidazole (1) and 4‐azabenzimidazole in DMSO‐d6 solutions. For the first compound, fast exchange between the two chelated structures prevails for 13C relaxation times, whereas proton and 13C chemical shifts characterize a slow exchange. For 4‐azabenzimidazole, 13C and 1H spectra do not exhibit absorptions from structures in slow exchange. Analysis of the T1 values of carbons 8 and 9 before and after isotopic exchange of the labile amino hydrogen clearly show that the major component of the equilibrium is the 3H structure.
13C NMR studies of polyaminocarboxylate complexes of Tl(III)
Authors: Anderegg G. , Popov K. , Pregosin P. S. 
Published: May 2005

AbstractThe 13C NMR characteristics of the polyaminocarboxylate ligands EDTA [(HO2CCH2)2NCH2CH2N(CH2CO2H)2],DTPA (HO2CCH2)2NCH2CH2N(CH2CO2H)CH2CH2N(CH2CO2H)2 and NTA [N(CH2CO2H)3] and their Tl(III) complexes are reported. The pH dependence of the 13C shifts of the ligands is helpful in understanding the 13C coordination chemical shifts, Δδ, but not the thallium‐carbon coupling constants J(205TI, 13C), which vary markedly for no apparent reason. The anion Tl(DTPA‐5H)2‐ contains three non‐equivalent coordinated carboxyl functions and a suggestion is made to account for this lower symmetry.
Rotational dynamics of molecules containing phenyl groups. A 13C spin‐lattice relaxation study
Authors: Dais Photis 
Published: May 2005

Abstract13C nuclear magnetic resonance spin‐lattice relaxation times (T1) have been used to probe the motional behavior of diphenyl compounds of the type PhXPh (X = heteroatom or group of atoms). Analysis of the relaxation data by employing Woessnier's formalism has permitted an investigation of the influence of the bridge on the rotation of the phenyl groups and the calculation of potential barriers to phenyl rotation in solution, which otherwise are inaccessible.
Multinuclear NMR study of variously substituted sulphonamides and sulphinamides
Authors: Ruostesuo P. , Häkkinen A.‐M. , Mattila T. 
Published: May 2005

Abstract13C, 15N and 17O NMR chemical shifts, and also 1J(CH) and 1J(NH) values, have been determined for variously substituted sulphonamides and some sulphinamides, either neat or in acetone or dimethyl sulphoxide solution.The effect of benzene ring substituents on the chemical shifts of nitrogen and oxygen nuclei is slight, but N‐substitution changes the shielding of both nuclei. Generally, an N‐methyl substituent shields an amide nitrogen and an N,N‐dimethyl substituent gives further slight shielding. On the other hand, an N‐phenyl substituent deshields the nitrogen strongly, but the deshielding effect of an N,N‐diphenyl substituent is markedly smaller. The sulphonyl oxygens are deshielded relative to the sulphinyl oxygens, and N‐methyl and N,N‐dimethyl substituents shield the oxygen nucleus. The effect of N‐phenyl and N,N‐diphenyl substituents on the shielding of the oxygen atoms of the sulphonyl group is slight.The direct 1J(CH) coupling constants are similar, but they are characteristic of different type of sulphur amides. The 1J(NH) values are of the same order of magnitude for sulphonamides and sulphinamides, but are clearly smaller for N‐unsubstituted amides than for N‐substituted compounds.
NMR studies of intramolecular proton exchange in alkylated naphthazarins
Authors: Elöve Gülnur A. , Schauble J. Herman 
Published: May 2005

AbstractThree groups of alkyl‐substituted naphthazarins were studied by 1H and 13C NMR in chloroform‐d at ambient temperature. Preliminary 1H NMR studies were carried out on selected members of each group at low temperatures (down to –120 °C) in dichloromethane‐d2 solution. Monoalkylnaphthazarins were found to exist predominantly as the 2‐alkyl tautomers (I) and the dimethylalkyl species as the 2,3‐dimethyl‐6‐alkyl tautomers (I). However, both symmetrically and unsymmetrically substituted 2,6‐ and 2,7‐dialkylnaphthazarins exhibited averaged chemical shifts and coupling constants indicating rapid proton exchange between the two minimum energy 1,4‐dione tautomers (I and II). 13C NMR shifts were utilized to calculate tautomer populations of the unsymmetrical 2,6‐ and 2,7‐(methyl,alkyl)naphthazarins.
Two‐dimensional NMR analysis of the phytohormone gibberellin A3
Authors: Preiss A. , Adam G. , Šaman D. , Buděšinsky M. 
Published: May 2005

AbstractThe complete analysis of the 1H NMR spectra of the phytohormone gibberellin A3 and its 3,13‐diacetyl derivative has been performed. ASIS and 2D J‐resolved spectroscopy were used to disentangle the complex spin systems, which were further analysed by 1H‐1H homocorrelated spectroscopy and spin decoupling. 2D 1H‐13C shift correlated spectra not only supported the identification of individual protons but also allowed the clarification of some controversial 13C assignments.
Assignment of carbonyl groups and sequence analysis in peptides by inverse correlation using long‐range couplings
Authors: Bermel Wolfgang , Griesinger Christian , Kessler Horst , Wagner Klaus 
Published: May 2005

AbstractInverse heteronuclear shift correlation via long‐range coupling to the carbonyl carbons of the cyclic hexapeptide cyclo(‐Phe11‐Thr10‐Aia9‐Trp8‐Phe/‐D‐Pro6‐) allows the sequential assignment of the amino acids. This experiment has a higher sensitivity than the conventional COLOC sequence.
Carbon‐13 chemical shifts and carbon‐proton coupling constants in 4H‐ and 9aH‐quinolizine esters and some of their methyl derivatives
Authors: Kamieńska‐Trela Krystyna , Raynes W. T. , Taylor B. F. 
Published: May 2005

AbstractThe proton coupled and decoupled 13C NMR spectra of 4H‐quinolizine 1,2,3,4‐tetracarboxylate and its less stable tautomer 9aH‐quinolizine 1,2,3,4‐tetracarboxylate have been investigated. All 13C resonances have been assigned, and a number of the one‐, two‐ and three‐bond carbon‐proton coupling constants obtained for these compounds and some of their methyl derivatives. The principal conclusion from the data is that the nitrogen atom is positively charged as a result of extensive conjugation.
NMR spectra of the porphyrins. 30—Calibration and application of a ring current model for cobalt(III) meso‐tetraphenylporphyrin (CoTPP) complexes
Authors: Abraham Raymond J. , Medforth Craig J. 
Published: May 2005

AbstractThe geometry of metalloporphyrin‐ligand complexes [mono‐(1:1) and bis‐(1:2)] produced by cobalt(III) meso‐tetraphenylporphyrin (CoTPP) with amine ligands has been investigated using the diamagnetic ring current shifts of the porphyrin on the ligand nuclei.The observed ring current shifts are corrected for complexation effects by the use of cobalt(III) dimethylglyoxime (DMG) complexes. Significant changes in ligand chemical shifts are observed on formation of a DMG complex, although saturated ligands only show changes at points close to the site of complexation.Crystallographic data and corrected ring current shifts for pyridine and N1‐methylimidazole are used to parameterize a double‐dipole model of the CoTPP ring current. For 4‐methylpiperidine a geometry calculated from corrected ring current shifts is in reasonable agreement with that observed in the solid state. The geometry calculated for a cyclohexylamine CoTPP complex can be rationalized in terms of a minimization of steric interactions with the porphyrin.Corrected 13C ring current shifts are still in poor agreement with calculated values, although there is a considerable improvement compared with uncorrected values.
Natural abundance 17O NMR spectra of coumarins, furocoumarins and related compounds
Authors: Duddeck Helmut , Rosenbaum Doris , Elgamal M. Hani A. , Shalaby Nagwa M. M. 
Published: May 2005

AbstractThe 54.2 MHz 17O NMR spectra of a series of naturally occurring coumarins and furocoumarins and those of a number of related model compounds are described. The 17O chemical shifts of the furocoumarins can be predicted by the evaluation of the data of substructures in model compounds. syn‐Periplanar γ‐ and long‐range interaction effects can be interpreted in terms of steric and electronic effects.
A 13C NMR study of hindered rotation in N1,N1‐penta‐ and N1, N1‐hexa‐methylene‐N2‐substituted‐phenylformamidines
Authors: Wawer Iwona 
Published: May 2005

AbstractRates of rotations about the C‐N1 partial double bond in a series of six N1,N1 penta‐ and six N1,N1‐hexa‐methylene‐N2‐substituted‐phenyformamidines were determined from 13C DNMR line shape analysis.Electron accepting substituents at the phenyl ring increase the barrier to rotation, and electron donating substituents decrease the barrier, compared with the nonsubstituted compound. Linear relationships are shown to exist between ΔG≠ and the 13C chemical shifts of the functional carbon or the pKa of formamidines.
Carbon‐13 NMR spectra of some c‐6 methylated steroids
Authors: Iida Takashi , Tamura Toshitake , Matsumoto Taro 
Published: May 2005

Abstract13C NMR signals were assigned for a series of C‐6 rnethylated steroids related to 5α‐cholestane, and the substituent effect of methyl groups at C‐6 on the shielding data is discussed.
13C, 17O and 1H NMR study of the protonation of acetone in water
Authors: Shen Lian‐fang , Du You‐Ru , Shao Qian‐fen , Mao Shi‐zhen 
Published: May 2005

AbstractThe protonation of acetone in water for a wide range of compositions of the binary mixture was studied by multinuclear NMR spectroscopy. Formation constants (K1 and K2) and 13C, 17O and 1H chemical shifts of the 1:1 and 1:2 complexes were evaluated. The correlation of the 1H chemical shift of uncombined water with its concentration, Δ
= A + B In [H2O]eq, recently derived for the trimethyl phosphate‐water system, was verified. A measure of the fraction of monomer species existing in the uncombined water at each composition was obtained. The results are discussed with respect to the structure of water.
High‐field proton NMR study of the liquid solution structure of monomeric bacteriochlorophyll a and chlorophyll a
Authors: Lötjönen S. , Michalski T. J. , Norris J. R. , Hynninen P. H. 
Published: May 2005

AbstractThe 500 MHz proton spectra of monomeric bacteriochlorophyll a and chlorophyll a were recorded and assigned. The proton chemical shifts and proton‐proton coupling constants were all determined except for the P‐5 to P‐15 phytyl side‐chain protons. The conformational structures of the reduced rings and associated side‐chains in these compounds were deduced from vicinal coupling constants. The reduced ring IV and the propionic ester side‐chain in bacteriochlorophyll a and chlorophyll a have identical conformations which, in addition, are very similar to those reported previously for methyl pheophorbide a and pheophytin a. The reduced ring IV of bacteriochlorophyll a, which is attached to the phytyl side‐chain, is more buckled than the other reduced ring (ring II).
Ring A conformation in steroids. 2—NMR study of C‐2 monomethyl‐ and dimethyl‐substituted 5α‐androstan‐3‐ones
Authors: Marat Kirk , Templeton John F. , Gupta R. K. , Kumar V. P. Sashi 
Published: May 2005

AbstractRing A proton shifts and couplings and 13C shifts of all carbons are given for 17β‐acetoxy‐2α‐methyl‐ and 17β‐methoxy‐2β‐methyl‐5α‐androstan‐3‐one and 2,2‐dimethyl‐17β‐methoxy‐5α‐androstan‐3‐one. It was concluded that the 2β‐methyl derivative exists with ring A in a regular chair conformation while the 2β‐methyl derivative exists with ring A in an inverted boat conformation with C‐2 and C‐5 at the bow/stern positions. The data for 2,2‐dimethyl‐17β‐methoxy‐5α‐androstan‐3‐one suggest an equilibrium of these two conformers.
NMR studies in the heterocyclic series XXX—Carbon‐13 NMR study of 5‐nitrofurfural derivatives
Authors: Mester B. , Claramunt R. M. , Elguero J. 
Published: May 2005

AbstractFifteen 5‐nitrofurfural imino derivatives with antitrypanosomiasic activity have been studied by 13C NMR spectroscopy. Chemical shifts have been assigned and 13C1H coupling constants have been measured.
13C, 31P and 1H NMR studies of chiral bis[(4R,6R)‐4,6‐dimethyl‐1, 3, 2‐dioxaphosphorinan‐2‐yloxy]alkane derivatives. Coupling between phosphorus atoms six bonds apart
Authors: Szalontai G. , Bakos J. , Tóth I. , Heil B. 
Published: May 2005

Abstract13C, 1H and 31P NMR investigations were carried out to confirm the stereochemistry of novel bis[(4R,6R)‐4,6‐dimethyl‐1,3,2‐dioxaphosphorinan‐2‐yloxy]alkanes. The 13C NMR spectra exhibited second‐order features at room temperature. Substantial coupling was found between P atoms six bonds apart. The possibility of a through‐space contribution was tested. Spatially close P atoms and the strongly electronegative P substituents (oxygen atoms) are thought to be responsible for the enhanced P… P coupling.
1H and 13C nuclear magnetic resonance of phenyldibenzophosphole and derivatives: Complete assignment using two‐dimensional J‐resolved and shift correlation methods
Authors: Nelson John H. , Affandi Salina , Gray George A. , Alyea Elmer C. 
Published: May 2005

AbstractProton and 13C NMR parameters have been determined for phenyldibenzophosphole and its oxide, sulfide, selenide and W(CO)5 complex from high‐resolution one‐ and two‐dimensional (COSY, HETCOR and 2DJ) experiments at 4.7, 7.1 and 9.4 tesla. Assignments of chemical shifts and coupling constants have been made and verified by computer simulation of the proton spectra. The data are discussed in relation to the geometry and electron density at phosphorus and the diamagnetic anisotropy of the W(CO)5 group.
A one‐dimensional selective version of the INADEQUATE experiment for determining carbon—carbon connectivities. Analysis of multi‐pulse experiments by a vectorial representation
Authors: Canet D. , Brondeau J. , Boubel J. C. , Retournard A. 
Published: May 2005

AbstractThe simple pulse sequence (π/2)x‐τ‐(π/2)‐x(π/2)φ(Acq)ψ allows selective polarization transfer from a nucleus A (on resonance) towards any nucleus X, J coupled to A, provided that τ is properly varied around ½J with coaddition of the relevant FIDs. With an appropriate phase cycling, parent signals in a natural abundance 13C spectrum are eliminated. This consequently leads to the unambiguous determination of all carbons coupled to A. A universal vectorial representation aimed at multi‐pulse sequence analysis is proposed and applied to the present experiment.
13C NMR chemical shifts, in some N‐chloro‐2,6‐diarylpiperidin‐4‐ones
Authors: Ul Hasan Misbah , Arab M. 
Published: May 2005

AbstractThe 13C shifts in several N‐chloro‐2,6‐diarylpiperidin‐4‐ones have been measured and compared with previously reported sifts in the corresponding 2,6‐diarylpiperidones. The shifts of the α‐carbons in these compounds move downfield by 12–13 ppm, which can be attributed to the increased electronegativity of the nitrogen atoms. The changes in the chemical shifts of the β‐carbons are minimal. Surprisingly, the absorptions of the carbonyl carbons move upfield by as much as 4.0 ppm. The magnitude of the shift in the resonance of the carbonyl carbon indicates the possibility of a transannular interaction between the nitrogen and the carbonyl group, which has not previously been observed in these systems. A preferred conformation for the aryl group in these compounds is also proposed.
NMR study of substituent effects in 4‐substituted and 4,4′‐disubstituted diphenyl sulphides
Authors: Chandrasekaran R. , Perumal S. , Wilson D. A. 
Published: May 2005

AbstractThe proton and carbon NMR spectra of nine 4‐X‐diphenyl sulphides (series 1), seven 4‐X‐4′‐NO2‐diphenyl sulphides (series 2) and eight 4,4′‐X2‐diphenyl sulphides (series 3) have been obtained. Correlation of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes (Lynch plots) show an enhancement of substituent effect at C‐1 (carbon para to the substituent) in series 1 and 2, but not in series 3. The carbons of the unsubstituted ring in series 1 also correlate with Cp‐SCS, with slopes of less than unity; correlation for C‐1′ has a negative slope. Dual substituent parameter (DSP) correlations of the 13C chemical shifts with σI/σoR are good to excellent for all the carbons of series 1 compounds, except those ortho to the substituent X. The carbons meta to the substituent X correlate well, but with negative values for ρI and ρR, although showing a scattered Lynch plot. Similar correlations are found with some carbon shifts in series 2, and with C‐1 shifts in series 3.It is concluded that (a) reverse resonance effects are operative at the position meta to the variable substituent by virtue of the sulphur substituent ortho to that carbon; (b) there is transmission of inductive (field) and resonance effects from one aryl ring to the other, except when both rings carry substituents of the same electronic character (series 3); (c) there is some evidence for π‐polarization in the unsubstituted phenyl ring of series 1 compounds.
Study of the monomer‐dimer equilibrium of nitrosobenzene using multinuclear one‐ and two‐dimensional NMR techniques
Authors: Orrell Keith G. , Šik Vladimir , Stephenson David 
Published: May 2005

AbstractThe monomer‐dimer equilibrium of nitrosobenzene in CDCI3 solution was studied in the temperature range ‐50 to 30 °C using 13C, 15N and 17O NMR spectroscopy. Decreasing temperature favours the dimeric azodioxy species, and below ca 10 °C both cis and trans dimers were detected in addition to the monomer. The relative abundance of the trans dimer is low (⩽6%) at all temperatures and this is the first report of its existence in solution. The monomer and dimer species were characterized by their 13C and 15N shifts, and exchange between them was measured quantitatively by 13C 2D‐EXSY spectra. Exchange occurred exclusively between the cis‐dimer and monomer and between the trans‐dimer and monomer, activation energies, ΔG≠(298.15 K) being 65.8±0.1 and 70.0±0.3 kJ mol−1, respectively.