bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton nuclear magnetic resonance study of phthalide and 2‐coumaranone partially oriented in nematic phases
Authors: Wong T. C. , Koval Kenneth J. 
Published: May 2005

AbstractThe 1H NMR spectra of phthalide in Merck Nematic Phase IV and in N‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline (EBBA) and of 2‐coumaranone in Merck Nematic Phase IV were analyzed. Structural parameters were obtained. The planarity of the 5‐membered ring and the molecular orientations were discussed.
Radical reactions in the coordination field of transition metals. VII—H‐transfer between phenolic and aryl‐aminic H‐donors and their radicals
Authors: Tkáč A. , Omelka L. 
Published: May 2005

AbstractAn ESR method for studying the mechanism of H‐transfer reactions between H‐donors of different reactivity (A1H, A2H…) and their free radicals (A1; A2.…) in non‐polar solvents at ambient temperature is presented. The new technique is based on a pulsed initiation of various secondary phenoxy or nitroxy radicals in binary mixtures of hindered phenols, unhindered phenols, partially hindered thiobisphenols and diphenylamine, employing a high concentration of free RO2. and coordinated (CoIII)RO2. tert‐butyl peroxy radicals generated in the redox‐reaction of Co(acac)2 with tert‐butyl hydroperoxide. The consecutive H‐transfer reactions proceed to equilibrium until the most stable radicals are formed. In this way criteria are obtained for ranking the compared free and coordinated phenoxy radicals according to their relative stabilities. The secondarily generated phenoxy radicals from unhindered phenols after coordination to CoIII are stabilized and cannot take part in further H‐transfer reactions.
Carbon‐13 nuclear magnetic resonance spectra of nicotine metabolites and related compounds
Authors: Nishida Toshiaki , Pilotti ÅKe , Enzell Curt R. 
Published: May 2005

AbstractThe potential of 13C NMR techniques for studies of nicotine metabolism has been investigated by acquisition and assignment of 13C NMR spectra of nicotine, its metabolites and some related compounds. It is shown that C‐2′ of nicotine would be the best site for 13C labelling when using the method to gain further insight into the metabolic pathways of nicotine.
Temperature dependence of 13C nuclear magnetic shielding in some aliphatic alcohols
Authors: Jackowski K. , Raynes W. T. 
Published: May 2005

AbstractThe 13C nuclear shielding in methanol, ethanol and isopropanol has been measured over the temperature range 186–325 K. Corrections to the observed shifts have been made to allow for the temperature dependence of the shielding of the external tetramethylsilane reference and for the temperature dependence of the bulk susceptibility effects in the alcohols. The results show that the temperature dependence of 13C shielding in the liquid alcohols is smaller than that in tetramethylsilane. By comparison both with temperature coefficients of compounds not involving hydrogen bonding and with N‐protonation studies, it is inferred that the reduction of hydrogen bonding which occurs in the liquid alcohols as the temperature is raised has very little effect on the 13C shielding. It is the change in the van der Waals forces which predominates in determining the temperature coefficient.
Carbon‐13 NMR spectra of bromine‐containing esters
Authors: Velichko F. K. , Dostovalova V. I. , Vinogradova L. V. , Kh. Freidlina R. 
Published: May 2005

Abstract13CHBrCOOR fragments of bromine‐containing mono‐ and dicarboxylates show 13C NMR signals in the range 38–45 ppm, at 12–15 ppm to high field of their chloro analogues. The introduction of one bromine atom into the α‐CH2 group causes a 6–13 ppm shift of the carbon signal, depending on the type of ester. The replacement of H with Br in 13CH2(COOR)2 has only a negligible influence on the 13CH2 signal position. The 13CBr2COOR fragment signals appear in the range 50–54 ppm. 13C NMR data, including the chemical shift values, signal multiplicities and spin‐spin couplings, make possible the identification of isomers present in isomer mixtures of bromine‐containing esters. The 13COOR chemical shifts of diastereomers of α,β‐dibromoesters differ noticeably from each other, and the 13C NMR spectra can thus be used to supply preliminary information about the stereochemistry of bromine addition to α,β‐unsaturated acids.
Selection of shift reagents for 17O NMR. Application to line assignments
Authors: Kintzinger Jean‐Pierre , Nguyên T. Thanh‐TâM 
Published: May 2005

AbstractChemical shifts and line broadenings induced by a series of lanthanide dipivaloylmethanates Ln(dmp)3 on the 17O NMR signal of methanol have been measured. The best high‐field shift reagents are those containing the cations Tb+3 and Dy+3; very large shifts have been observed for even quite low concentrations of reagent. The shift reagents are able to discriminate between different oxygen functions and can, in principle, be used for line assignments.
Primary and secondary binding sites for lanthanide shift reagents with amides. Differential behavior of cis vs trans amide isomers with LSR
Authors: Graham Laurine Laplanche 
Published: May 2005

AbstractLanthanide induced shifts (LIS) were measured for four dimethylamides, RCON(CH3)2, and four monomethyl amides, RCONHCH3, R  H, CH3, CF3 and CCl3, using Eu(fod)3 in CCl4 and benzene (C6D6) solution. Structural correlations for HCON(CH3)2 and CH3CON(CH3)2 in both solvents yield a preferred binding site for the Eu(fod)3 on one of the lone‐pair orbitals of the oxygen atom, with a probable site of secondary importance on the other lone‐pair orbital. The cis vs trans isomers of HCONHCH3 and CH3CONHCH3 exhibit remarkably different chemical shift behavior upon addition of Eu(fod)3.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Differential rates of NH proton‐exchange reactions of hydrazine‐carbothioamide and 4‐methylhydrazine‐carbothioamide in dimethyl sulfoxide
Authors: Yavari Issa , Roberts John D. 
Published: May 2005

AbstractThe proton‐coupled nitrogen‐15 NMR spectra of hydrazinecarbothioamide and 4‐methylhydrazinecarbothioamide have been taken at the natural‐abundance level in neutral, basic and acidic solutions at 25°C. The NH proton‐exchange reactions of the hydrazino‐NH2 groups in both compounds were found to be very rapid in the presence of acid, but quite slow in the presence of base. The hydrazino‐NH protons of hydrazinecarbothioamide exhange six times and 200 times faster than the amide protons in the presence of either base or acid, respectively. Similarly, acid‐ and base‐catalyzed NH proton exchanges of the hydrazino‐NH group of 4‐methylhydrazinecarbothioamide were found to be two to three orders of magnitude faster than those of N‐methylamido protons. These results can be rationalized by consideration of the effect of the lone pair on the hydrazinoNH2 group on the reactivity of the adjacent NH group.
High resolution NMR spectroscopy of heteroaromatic cations. I. 13C1H coupling constants in the pyridinium cation
Authors: Sándor P. , Radics L. 
Published: May 2005

AbstractHigh‐resolution 1H{14N} and proton‐coupled natural‐abundance 13C{14N} double resonance spectra have been recorded for pyridinium tetrafluoroborate dissolved in CD3CN. Iterative analysis of these spectra has provided the accurate values and relative signs of all possible long‐range 13C—1H coupling constants. These are compared with the respective values in pyridine and pyridine‐N‐oxide and discussed in terms of the relationship with the electronegativity of the N‐substituent. Experimental conditions allowing the observation of well‐resolved proton‐coupled 13C NMR spectra of charged heteroaromatics are also presented.
Carbon‐13 nuclear magnetic resonance studies of anthraquinones Part II—hydroxymethoxyanthraquinones, acetoxymethoxyanthraquinones and naturally occuring anthraquinone analogues
Authors: Berger Y. , Castonguay A. , Brassard P. 
Published: May 2005

AbstractThe 13C NMR spectra of hydroxymethoxyanthraquinones, acetoxymethoxyanthraquinones and naturally occuring anthraquinone derivatives are reported and all chemical shifts assigned. Hydroxy, methoxy and acetoxy substitution parameters are additive except in the case of 1,2‐disubstitution and for 1‐hydroxyanthraquinones substituted on C‐3 or on C‐4 by an hydroxy or a methoxy group. In anthraquinones substituted on C‐2, carbon shieldings are found to be sensitive to steric interference and to conjugative electron release by the 1‐OCH3.
Radical reactions in the co‐ordination field of transition metals. VIII—σ‐phenoxy and σ‐cyclohexadienoneoxy radicals co‐ordinated to cobalt (III) and their generation by tert‐butylperoxy radicals or by molecular oxygen complexed to cobalt
Authors: Tkáč A. , Omelka L. 
Published: May 2005

AbstractThe formation of a ternary complex between phenols, Co (II)‐acetylacetonate and molecular oxygen has been established at ambient temperature and in non‐polar solvents. After intramolecular electron transfer the transient magnified image radical enhances the homolytic scission of the OH bond of the complexed phenol. The low g value of the observed ESR spectra, the net spin delocalization to the cobalt nucleus and the interaction of the unpaired electron with only a limited number of benzene ring protons, indicate the presence of co‐ordinated s̀‐phenoxy radicals generated from unhindered phenols (g = 2.0006 ∼ 1.9997) and of co‐ordinated s̀‐cyclohexadienoneoxy radicals generated from hindered phenols (g=1.9990 ∼ 1.9980). Without the cobalt‐chelating acetylacetonate ligands neither the co‐ordinated s̀‐phenoxy nor the co‐ordinated s̀‐cyclohexadienoneoxy radicals can be prepared, whereas co‐ordinated π‐tert‐butylperoxy radicals [Co(III)BuO2·] are generated in a high concentration during the reaction of tert‐butyl hydroperoxide with CoCl2 in acetone.
Dynamic stereochemistry at sp2sp3 bonds part 1—the use of heterocyclic models for quantitative studies of steric effects of alkyl groups
Authors: Roussel Christian , Gallo Roger , Metzger Jacques , Sandström Jan 
Published: May 2005

AbstractThe barriers to rotation of the 3‐substituent in six 3‐RCH2‐4‐Me‐δ4‐thiazoline‐2‐thiones (R  Me, Et, Pr, Isobu, Isopr,t‐Bu) and in two analogous methiodides have been measured by the 1H DNMR technique. The barriers are discussed in relation to the possible conformations of the transition states, and comparisons are made with barriers to rotation of the same substituents in other frameworks. It is concluded that the relative steric effects are strongly dependent on the framework and that, in general, a conformational analysis of the individual cases is necessary to understand the steric effects of alkyl groups.
Quantitative 15N NMR spectroscopy
Authors: Levy George C. , Pehk T. , Srinivasan P. R. 
Published: May 2005

AbstractLine intensities in 15N NMR spectra are strongly influenced by spin‐lattice and spin–spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 15N NMR of molecules with different nitrogen functional groups and also mixtures of nitrogen‐containing compounds. It is shown that, in general, quantitative data are obtainable from integration of 15N lines in proton decoupled 15N NMR spectra using NOE suppression. Addition of paramagnetic relaxation reagents (PARR) under controlled conditions is frequently needed to accomplish the experiment within reasonable time limits.
Restricted rotation of the C6F5 ligand in cyclopentadienyl π‐complexes of titanium (IV)
Authors: Leblanc Jean Claude , Moïse Claude 
Published: May 2005

Abstract1H and 19F spectra of methoxypentafluorophenyltitanocene complexes have been analysed. They show the possibility of coupling between the methyl protons of the methoxy group and the two ortho fluorine atoms of the pentfluorophenyl ligand. Furthermore, anisochrony of the two ortho and the two meta fluorine atoms is detected in some cases. The analysis of conformational factors is presented.
Dynamic stereochemistry at sp2sp3 bonds part II—the importance of ground‐state strain in the determination of apparent spatial requirements of substituents
Authors: Roussel Christian , Blaive Bruno , Gallo Roger , Metzger Jacques , Sandström Jan 
Published: May 2005

AbstractThe barriers to rotation of RCH2 groups (R  Me, Et and Isopr) as 3‐substituents in 4‐Me‐δ4‐thiazoline‐2‐thiones, their 4‐t‐Bu analogues, and the methiodides of the latter compounds have been studied by 1H DNMR and by molecular mechanics calculations. The barriers in the 4‐t‐Bu compounds are rather insensitive to the size of R, which is shown to be caused by strain in the ground state. More generally, it is shown that when δG‡ values are used in various methods for estimating the apparent spatial requirements of substituents, such ground‐state strain may lead to erroneous results in non‐circumspect treatments.
Application of 13C NMR to the study of the tautomerism of some disymmetric triazenes: The 3‐aryl‐1‐(3,4‐dimentyl‐5‐isoxazolyl)triazenes
Authors: Vernin G. , Siv C. , Bouscasse L. , Metzger J. , Faure R. , Vincent E. J. , Párkányi C. 
Published: May 2005

AbstractThe 13C NMR spectra of some 1,3‐diaryltriazenes, 3(1)‐aryl‐1(3)‐hetaryltriazenes and their methylated derovatives have been recorded. From the comparison of the 13C chemical shifts between 3‐aryl‐1‐(3,4‐dimethyl‐5‐isoxazolyl)triazenes 1 and compounds with fixed structure, such as 1‐aryl‐3,3‐dimentyltriazenes and methylated derivatives of 5‐amino‐3,4‐dimethylisxazole, we found that the triazenes 1 have the sturcture (A) in which the azo group is conjugated with the heterocycllic moiety. para‐Substituent on the aromatic ring have a week influence on the displacement of this tautomeric equilibrium. 13C NMR gives only qualitatives results. Theoretical calculation (HMO, CNDO‐2) are also consistent with the greater stability of tautomeric form A.
Radical reactions in the co‐ordination sphere of transition metals. X—radicals derived from 4,4‐biphenyldiols, 4,4′‐thiobisphenols and bis(4‐hydroxybenzyl)sulphide
Authors: Tkáč A. , Omelka L. , Jiráčková L. , Pospíšil J. 
Published: May 2005

AbstractUsing the analysis of the splitting constants of the ESR spectra, factor are described which affect the stability of free phenoxyls and of phenoxyls co‐ordinated on cobalt, generated by the reaction of tert‐butyleperoxyls and 4,4′‐biphenyldiols (1), 4,4′–thiobisphenols (2 and 5), 4,4′‐dithiobisphenol 3a, the 4,4′‐trithiobisphenol 3b, di(3,5‐di‐tert‐butyl‐4‐hydroxybenzyl) sulphide (4a) and its corresponding sulphoné (4b). Phenoxy radicals are formed from compounds of type 1–4 in the presence and in the absence of oxygen. In the case of generation with oxygem complexed to cobalt, compounds 4, for steric reasons, form co‐ordinated radicals of the cyclohexadienonyloxyl type. Free phenoxyls are also formed from 2a–2c, 3a and 3b as a result of the direct transfer of electrons from the sulphur non‐bonding electron pair to the peroxidic bond of tert‐butyl hydroperoxide in the absence of cobalt.
Selenium‐77 magnetic resonance in SSe and SeSe isosteres of phenanthrene
Authors: Baiwir Marcel , Llabrès Gabriel , Piette Jean‐Louis , Christiaens LÉOn 
Published: May 2005

AbstractSelenium‐77 magnetic resonance spectra of sulphur‐selenium and selenium‐selenium isosteres of phenanthrene and some of their 2‐substituted derivatives have been recorded and 48 77Se chemical shifts are presented. The two isomers of the studied compounds could be differentiated because the Se nucleus is always more shielded in the ‘trans’ than in the ‘cis’ isomer, the difference varying between 10 and 40 ppm. CNDO calculations have been performed; they allow an electronic model to be proposed which accounts, at least qualitatively, for the NMR results. They also provide an electronic interpretation of the ring opening of the Se‐containing ‘cis’ isomers when treated with alkyllithium.
The carbon‐13 NMR spectrum of dimethoxybilirubin dimethyl ester
Authors: Kaplan Doron , Navon Gil 
Published: May 2005

AbstractThe 13C NMR spectrum of dimethoxybilirubin dimethyl ester (1) is reported. Methoxyvinylneoxanthobilirubinic acid methyl ester, a compound containing one endo‐vinylpyrromethene unit, was prepared and used in the assignment of the spectrum of 1.
Nitrogen inversion in 3,6‐dihydro‐1,2‐oxazines
Authors: Labaziewicz Henryk , Riddell Frank G. 
Published: May 2005

AbstractThe nitrogen inversion barriers of nine 3,6‐dihydro‐1,2‐oxazines are discussed. Polar solvents were found to increase the nitrogen inversion barriers which, in turn, decrease with increasing size of the N‐substituent.
Cyclic oxonium salts: 13C magnetic resonance spectroscopy. The correlation of chemical shifts with the calculated charge density
Authors: Bégué J. P. , Bonnet‐Delpon D. 
Published: May 2005

AbstractThe 13C chemical shifts of several bicyclic and monocyclic oxonium salts are reported and, in the case of 5‐membered ring unsaturated oxonium salts, compared with ab initio and CNDO calculated charges. A prime dependence of the 13C shielding on the π charge delocalization effects induced by the Y group is established for the Y‐substituted C‐α carbon; a good correlation of δC‐α vs qπ is obtained, using π bond‐order terms. However, contradictory information arises from NMR and theoretical calculations for the C‐ω carbon, which is distant from the Y group. The results are discussed.
14N nuclear quadrupole resonance study of substituted anilines and prediction of in vitro activity of sulfanilamides
Authors: Greenbaum S. G. , Subbarao S. N. , Bray P. J. , Oja T. 
Published: May 2005

Abstract14N nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines are reported and analyzed in the framework of the Townes and Dailey theory. Satisfactory correlations of the NQR data with both the Hammett σ parameters and the in vitro biological activities of the corresponding sulfanilamides have been found. The results obtained suggest that the nitrogen lone‐pair orbital is more sensitive than the nitrogen–carbon sigma orbital is to substituent effects.
Studies of substituent effects by carbon‐13 NMR spectroscopy. Thiophene and furan chalcone analogues
Authors: Musumarra Giuseppe , Ballistreri Francesco P. 
Published: May 2005

Abstract13C NMR spectra of 39 thiophene and furan chalcone analogues in CDCl3 solutions are reported. The effect of substituents on the 13C chemical shifts in the phenyl and in the 5‐membered rings is discussed. 13C NMR shifts are correlated with Hammett parameters and with experimental shifts in the chalcone series.
Conformational studies of 3‐amino‐3‐phosphonatopropionic acid. 1H31P coupling constants
Authors: Siatecki Zdzisław , Kozłowski Henryk 
Published: May 2005

AbstractThe 1H and 31P NMR spectra of 3‐amino‐3‐phosphonatopropionic acid, a phosphonic derivative of aspartic acid, have been measured and completely analysed for 14 pH values. The vicinal coupling constants, 3J(HH) and 3J(HP), were used to obtain information on the rotational isomerism of the amino acid. The most stable conformer is the one where the phosphonic and β‐carboxyl groups are in trans position to each other.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. 15N19F coupling constants in fluoropyridines and fluoroanilines
Authors: Sibi Mukund P. , Lichter Robert L. 
Published: May 2005

AbstractTwo‐to five‐bond 15N19F coupling constants have been determined for fluoropyridines, 8‐fluoroquinoline, fluoroanilines and fluoroaniline derivatives. Only in 2‐fluoropyridine is J(NF) large, and this is associated with a lone pair mediated enhancement of the coupling. Values in fluoroanilines and derivatives are <2Hz. Except for the fluoroanilines themselves, J(NF) decreases inversely with the number of intervening bonds. In the anilines, only 5J(NF) is observable. Possible influences of lone pair interaction and hydrogen bonding are discussed.
Inhibition and enhancement of resonance as studied by 13C nuclear magnetic resonance spectroscopy
Authors: Kitching William , Jonge Ian De , Adcock William , Abeywickrema Anil N. 
Published: May 2005

Abstract13C chemical shifts are reported for a series of 2‐substituted 1,3‐dimethylbenzenes: comparisons of these values with those for the corresponding monosubstituted benzenes reveal, in some cases, large differences in the para‐carbon substituent chemical shifts, which are attributable to steric hindrance of resonance. The questions of steric enhancement of resonance, and methoxy group conformation in certain anisoles are also studied by the 13C NMR technique. Studies of selected 2‐substituted fluorenes are also reported, and substituent chemical shifts at carbon‐7 (traversing eight bonds) of greater than 2ppm are observed. These effects are consistently greater than those reported for the corresponding biphenyl compounds, and are associated with planarity‐enforced enhancement of resonance.
NMR chemical shift substituent effects: 2‐α‐monosubstituted N,N‐diethylacetamides
Authors: Martins Marcos A. P. , Rittner Roberto 
Published: May 2005

Abstract1H NMR chemical shifts for some α‐hetero‐substituted N,N‐diethylacetamides were recorded. The resonance assignments for the syn‐ and anti‐methylene and ‐methyl protons have been made unambiguously through their aromatic solvent induced shifts and are opposed to the literture assignments for the N‐methylene protons. An empirical relationship between the Charton polar (σL) and steric (V) parameters and the α‐methylene proton resonances was found. The N‐methylene proton chemical shifts also showed a qualitative dependence on the α‐substituent electronegativity, while the N‐ethyl methyl proton chemical shifts were related to the α‐substituent steric effects. The Paulsen and Todt anisotropic model and the more populated rotamers proposed seem to explain the results very well.
Nitrogen‐15 coupling constants: Geminal coupling, 2J(15NH), in cis‐ and trans‐aldonitrones and vicinal coupling, 3J(15NH), in cis‐and trans‐ketimines, oxaziridines and nitrones
Authors: Boyd Derek R. , Stubbs Michael E. , Thompson N. J. , Yeh Herman J. C. , Jerina Donald M. , Wasylishen Roderick E. 
Published: May 2005

AbstractNitrogen‐15‐hydrogen 2J(15NH), 15N, 13C 1J(15N13C) and 13C, H 1J(13CH) coupling constants have been measured and their signs determined for cis‐and trans‐[9‐anthryl(13C)methylene](2H3)methylamine (15N)‐oxide. Values of 2J(15NH) were of similar magnitude (∼2 Hz) but were of opposite sign. The results are compared and contrasted with those reported for related imino and quaternary imino systems. Vicinal 3J(15NH) coupling constants have been measured in cis‐ and trans‐15N‐[1‐(α‐naphthyl)ethylidene]benzylamine and 15N‐[1‐(p‐nitrophenyl)ethylidene]‐t‐butylamine and were found to be larger when the imino methyl group was cis to the nitrogen lone pair. The corresponding cis and trans ketonitrones formed by photoisomerization of the derived oxaziridines had 3J(15NH) values of c. 3.3 Hz. A study of the signs and magnitudes of observed and calculated 15N,H coupling constants for all of the 15N labelled imines, oxaziridines, imine N‐oxides (nitrones) and similar model systems which were synthesized is described.
The fixed conformation of the leucyl side‐chain in a tripeptide
Authors: Abraham Raymond J. , Jackson J. Timothy , Thomas W. Anthony 
Published: May 2005

AbstractThe complete analysis of the 1H NMR spectrum of the leucyl side‐chain of a tripeptide allows the deduction of the conformation of this side‐chain. In the peptide, in contrast to the free amino acid, the side‐chain is in a single fixed conformation.