bluuebunny/crossref_metadata_2025_split huggingface dataset:
The interaction between paramagnetic relaxation reagents and carbon tetrachloride
Authors: Edlund Ulf , Grahn Hans 
Published: May 2005

AbstractThe 13C spin‐lattice relaxation times for carbon tetrachloride have been measured in the presence of various paramagnetic chromium (III) chelates (PARRs). The T1 values were compared with those of an inert standard, cyclohexane. A specific PARR: carbon tetrachloride interaction was clearly indicated, which is less obvious for bulky ligands or ligands having electron‐withdrawing substituents. The electron‐nuclear relaxation model and the quantitative description of outer‐sphere complexation is briefly discussed.
Determination of the stereochemistry of the monomethylated homologues of 1‐chloro‐ and 1‐bromo‐1‐methylcyclobutane by means of NMR spectroscopy
Authors: Hittich Reinhard 
Published: May 2005

AbstractThe 300 MHz 1H NMR spectra of 1‐chloro‐ and 1‐methylcyclobutane and all monomethylated homologues are reported and analysed with regard to the ring conformations. The results indicate that halogen substituents in methylated halocyclobutanes have a greater preference for the pseudo equatorial position than do methyl groups. The 13C NMR spectral data are given, and substituent parameters for halogen substituents and methyl groups are calculated. Of note are the variable γ effects, especially the remarkable difference between the γ‐methyl effects of the stereo‐isomeric 1,3‐substituted cyclobutane compounds.
An NMR, ESR, ENDOR and TRIPLE resonance investigation of a cation radical formed from 1,2,4,5‐tetramethoxybenzene
Authors: Fairhurst S. A. , Smith I. M. , Sutcliffe L. H. , Taylor S. M. 
Published: May 2005

AbstractSeveral methods have been established for preparing cation radicals from 1,2,4,5‐tetramethoxybenzene that allow highly resolved ESR spectra to be recorded. Precise values of the hyperfine coupling constants for the aromatic and methoxy protons have been obtained; the values are 0.2268±0.0004 and 0.0863±0.0002 mT, respectively, with dichloromethane as solvent. No temperature dependence is evident. TRIPLE resonance experiments showed that both coupling constants have the same sign. NMR experiments provided contact shift and line broadening measurements; these proved that both the above constants are positive and led to a value of 3.1 (±0.3)×108M−1 s−1 at 23°C for the rate constant for electron exchange between the cation radical and the parent compound.
Application of NMR spectroscopy of chiral association complexes. 12—rate determination of an intramolecular motion in a free molecule by means of dynamic NMR measurements in the presence of an auxiliary compound
Authors: Küspert Reinhard , Mannschreck Albrecht 
Published: May 2005

AbstractThe rate constants of intramolecular processes can sometimes be measured only in the presence of optically active auxiliary compounds. The problem of obtaining the rate for the free molecule was solved by linear extrapolation of rate constant from the complexed to the uncomplexed molecule (LERCUM). This method is developed theoretically and checked experimentally. 2‐Bromo‐2‐methyl‐1‐(3‐bromo‐2‐methoxy‐4,5,6‐trimethylphenyl)‐1‐propanone has the advantage that rotation about its carhonyl‐to‐aryl bond can be measured both in the presence of (+)−2,2,2‐trifluoro‐1‐phenylethanol as well as in the absence of an auxiliary compound. The novel method of extrapolation is confirmed by the agreement between both results.
13C NMR spectral study of polyacetoxyxanthones. IV—13C NMR spectroscopy of substituted xanthones
Authors: Chaudhuri R. K. , Frahm A. W. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of nine acetoxyxanthones are reported and identified. The acetoxy substituent effects have been evaluated and the corresponding shift increments proposed.
High resolution 13C and 1H NMR spectral analysis of 1‐azafluorene
Authors: Fomichov A. A. , Svoren V. A. , Golovtsov N. I. , Soldatenkov A. T. , Prostakov N. S. 
Published: May 2005

AbstractAn analysis of the 1H and 13C spectra of 1‐azafluorene has been carried out using computer calculations and homo‐ and heteronuclear double resonance techniques. The 4J, 5J and 6J long‐range coupling constants of the 9‐CH2 group protons with the protons of the pyridine and the phenylene rings have been observed and measured. The long‐range J(CH) values in the 1H coupled 13C spectrum have been assigned and measured on a first‐order basis.
Studies on olefins. IX—proton NMR study of some CH2CR1R2 and CHR3CR1R2 alkenes
Authors: Rummens Frans H. A. , Lomas John S. , Tiffon Bernard , Coupry Claude , Lumbroso‐Bader Nicole 
Published: May 2005

AbstractThe proton NMR spectra of 2,3,4,4‐tetramethyl‐3‐t‐butylpent‐1‐ene rotarners have been completely assigned by low temperature NOE measurements. Chemical shifts and cis and trans allylic coupling constants are unambiguously determined. It is shown that other 2‐substituted propenes can be assigned on the basis of the coupling constants, but not from the chemical shift data. In 1,2‐disubstituited propenes, however, the transoid coupling constant falls in the range of the cisoid coupling constant values of the 2‐substituted propenes. Coupling constants cannot, therefore, be used in the 1,2‐disubstituted propene series as a criterion for determining structure.
NMR chemical shift method in magnetic susceptibility measurements applied to studies of the reaction of cobalt complexes with cumene hydroperoxide
Authors: Trzeciak A. M. , Ziółkowski J. J. 
Published: May 2005

AbstractThe NMR chemical shift method was applied for the determination of the magnetic susceptibility of paramagnetic transition metal complexes in solution. The method was found to be very useful for the determination of magnetic susceptibility changes during a chemical reaction in which one paramagnetic compound produced another. The concentrations of two paramagnetic cobalt complexes [Co3O(O2CCH3)6(HO2CCH3)3] and Co(O2CCH3)2, were calculated from the chemical shift value observed during their reaction with cumene hydroperoxide. The results are consistent with those obtained from electronic spectra.
An examination of the 13C NMR phenyl substituent effect in branched and non‐branched alkyl systems
Authors: Hearmon R. A. 
Published: May 2005

AbstractLiterature and unpublished data on alkylbenzenes have been analysed to give phenyl substituent effects. The effects have been determined for non‐α‐branched, α‐branched and α,α‐branched alkyl groups.
Structural studies of carbanionic species α to a phosphoryl group; anion from ketophosphonate comparison with related enoxysilanes and p‐ylid
Authors: Bottin‐Strzalko Tekla , Seyden‐Penne Jacqueline , Pouet Marie‐José , Simonnin Marie‐Paule 
Published: May 2005

AbstractThe structure of the carbanionic species 4 formed from diethyl(2‐oxopropyl)phosphonate and t‐BuOK has been studied by 1H, 13C and 31P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4Z (C) is observed. Two slowly interconverting species 4Z and 4E co‐exist when the anion‐cation interaction is loose, i.e. in Me2SO and when the gegenion K+ is complexed to (2,2,2)cryptand in Me2SO. The anionic carbon of 4Z and 4E is planar, and they have a strong enolate character as shown by the barrier to rotation around the C‐1C‐2 bond (ΔGc‡∼92 KJ mol−1). Their structures are compared to those of the related E and Z 1‐diethylphosphonato‐2‐trimethylsilyloxypropenes and to (acetylmethylene)triphenylphosphorane.
Carbon‐13 NMR investigation of some pharmacologically important cyclic n‐alkynylamines
Authors: Al‐Rawi Jasim M. A. , Behnam George Q. , Salman Salman R. , Muhi‐Eldeen Zuhair , Al‐Jawad Fuad H. 
Published: May 2005

Abstract13C NMR spectra (22.63 MHz) of 23 cyclic amine derivatives of N‐alkynylphthalimides, N,N′;‐dialkynylpyromellitic acid diimides, N‐alkynyloxyphthalimides and 5‐p‐chlorophenyl‐2‐(4‐t‐amino‐2‐butynyl)thio‐1,3,4‐thiadiazoles were analysed. The influence on the 13C chemical shift of oxygen insertion between the nitrogen of the phthalimides and the methylene group was summarized.
Regio‐ and stereoselective alkylation of a pyrrolidinic system: Structural and conformational studies by high field NMR techniques
Authors: Schaefer M. , Faller P. , Nicole D. 
Published: May 2005

AbstractA new merocyanine was prepared by addition of the pyrrolidine enamine of N‐ethoxycarbonylpyrrolidine‐3‐one to 1‐octyne‐3‐one. This addition was regioselective (with an unexpected C‐4 alkylation of the pyrrolidinone‐3‐enamine) and stereospecific (exclusively trans addition to the triple bond). The structure and conformational equilibrium were studied by high resolution proton magnetic resonance (NOE and variable temperature effects). Activation parameters ΔH*, ΔS* and ΔG* are given, and the behaviour on protonation examined.
Some calculations of solvent effects on one bond NC spin–spin couplings
Authors: Shargi S. N. , Webb G. A. 
Published: May 2005

AbstractThe solvaton model, incorporating INDO parameters and commonly encountered perturbation procedures, is employed to obtain the variation of 1J(N≡C) as a function of the dielectric of the medium (ϵ) for some cyanides and isocyanides. In all cases considered 1J(N≡C) is predicted to become increasingly negative as ϵ increases. Changes of up to 2 Hz in 1J(N≡C) are expected, with the isocyanides being more sensitive than the cyanides to a change in ϵ.
Ring distortion effect on δ13C values of bicyclo[4.n.0] alkanes
Authors: Metzger P. , Cabestaing C. , Casadevall E. , Casadevall A. 
Published: May 2005

AbstractThe 13C NMR spectra of trans‐ and cis‐fused bicyclo[4.n.0]alkanes, where n=4, 3 and 2, were determined. The distortion of the six membered ring, which is due to the strain arising from the 1,2 fusion of cyclohexane with a smaller ring, is apparent mainly for the chemical shifts of the ring junction carbons. Both for the trans‐and for the cis‐fused hydrocarbons the results support a cyclohexane in a chair conformation, distorted to a different degree according to the size of the other ring. The geometries of the different compounds in the series were calculated.
The use of Sn satellites in 1H NMR spectra of oriented molecules. The structure of phenyltin trichloride
Authors: Diehl P. , Amrein J. 
Published: May 2005

AbstractThe proton spectra of phenyltin trichloride including 119Sn‐ and 117Sn‐satellites have been analysed in isotropic and in oriented solvents. The indirect as well as the direct proton‐proton and proton‐tin coupling constants have been measured. From these the proton‐proton and proton‐tin internuclear distances corrected for harmonic vibrations have been derived.
1H NMR study of bacteriochlorophyll a radical anion: Use of difference spectra
Authors: Brereton Richard G. , Sanders Jeremy K. M. 
Published: May 2005

AbstractThe radical anion of bacteriochlorophyll a has been monitored by observing differential electron transfer broadening in the 1H NMR spectrum of diamagnetic bacteriochlorophyll in the presence of a small amount of chemically produced anion. The use of NMR difference spectra clearly indicates which sites in the anion have greatest spin density; these data are compared with other studies on the cation and anion.
Radical reactions in the co‐ordination sphere of transition metals. XIIIRadicals derived from 4,4′‐ and 2,2′‐Alkylidenebisphenolic Antioxidants
Authors: Omelka L. , Tkáč A. , Jiráčková L. , Pospíšil J. 
Published: May 2005

AbstractRadical species were generated from 4,4′;‐ and 2,2′;‐alkylidenebisphenols during oxidation with free and co‐ordinated [Co(III)]RO2˙Radicals. This simulates the participation of bisphenolic antioxidants in the process of stabilization of hydrocarbons. Phenoxyls are primarily formed, and, depending on the character of the alkylidene bridge, some of them are gradually transformed into phenoxy radicals of the galvinoxyl type. Oxidation of alkylidenebisphenols by oxygen complexed to Co(II) yields co‐ordinated cyclohexadienonyloxy radicals. The character of the alkyl substituents on the phenolic nuclei specifically influences the stability of the generated phenoxy radicals at the applied temperature. The ESR characteristics of the primarily formed phenoxyls, phenoxyls of the galvinoxyl type and co‐ordinated cyclohexadienonyloxyls are discussed.
Carbon‐13 nuclear magnetic resonance studies on dichloropyridoquinolines
Authors: Molock Frank F. , Boykin David W. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts are reported for six angular and one linear dichloropyridoquinolines in CDCl3. The chemical shift assignments have been made using model compounds, fully coupled spectra, selective proton decoupling and results from lanthanide shift studies. Chlorine substituent effects are compared to those reported for chloroquinolines. The effect of the heteroaromatic nitrogen atoms on 13C1H coupling constants in these polycyclic systems are compared to those reported for pyridine systems.
NMR chemical shift substituent effects. 3—α‐Monosubstituted N,N‐diethylacetamides; bifunctional compounds in LSR experiments
Authors: Gutierrez Maria Alejandra , Martins Marcos A. P. , Rittner Roberto 
Published: May 2005

AbstractLanthanide‐induced shifts have been measured for some α‐heterosubstituted N,N‐diethylacetamides, using Eu(fod)3 in CCl4 solution. The resonances for the syn‐ and anti‐methylene and ‐methyl protons have been assigned unambiguously for some of these bifunctional amides. A simplified approach to the analysis of the geometry of the LSR–amide complexes is advanced, yielding average conformations which differ from the rotamers previously proposed. It demonstrates that the conformational equilibria are strongly perturbed by the lanthanide addition. The lanthanide was found to complex with the carbonyl oxygen atom lone‐pair in the less hindered position for some of the amides investigated, whereas the geometry of the complexes could not be determined for α‐(NN‐dimethyl)amino‐ and α‐methoxy‐N,N‐diethylacetamide. Mono‐ and bifunctional model compounds have also been measured to confirm the resonance assignments and the amide complexing site.
Conformational analysis of hydrazones.1H dynamic nuclear magnetic resonance and solvent effects in aryl‐ and 2‐furylaldehyde ethylaminoacetylhydrazones
Authors: Benassi Rois , Benedetti Adriano , Taddei Ferdinando , Cappelletti Roberto , Nardi Dante , Tajana Alberto 
Published: May 2005

AbstractAryl‐ and 2‐furylaldehyde ethylaminoacetylhydrazones were examined in different solvents and over a wide temperature range with1H NMR in order to study their conformational properties. Nearly equal amounts of theE/Zisomers, relative to the CN bond, are present, even when the solvents and the substituents on the aldimino carbon produce small changes in the isomeric mixture. The activation parameters of the thermal isomerization process were measured, and the results are in the line with a lateral‐shift type mechanism, also supported by theoretical calculations on a model compound. No other internal process was noted from the low‐temperature spectral behaviour, and this was interpreted in terms of a highly biased equilibrium concerning the rotation around the C(O)N bond. Chemical shifts obtained in different solvents also enable the most stable arrangement of the whole molecule of these compounds to be postulated.
Some INDO calculations of 1J(PN) values
Authors: Duangthai S. , Webb G. A. 
Published: May 2005

AbstractSelf consistent perturbation theory calculations of 1J(PN) are performed using INDO parameters. The change in sign of the coupling upon passing from tri‐ to penta‐valent phosphorus arises from the influence of the phosphorus lone‐pair electrons. The observed coupling trends are reproduced by the variation in the contact contribution which, in turn, depends largely upon the s character of the lone‐pair electrons on the coupled nuclei. There appears to be no significant role played by the phosphorus d orbitals in the couplings considered.
A proton NMR analysis of the OCH3 group conformation in 2‐methoxypyridines
Authors: Contreras R. H. , Facelli J. C. , de Kowalewski D. G. 
Published: May 2005

AbstractThe absence of HH couplings between the methoxy group and the ring protons observed in 2‐methoxy‐, 2,6‐dimethoxy‐ and 2‐methoxy‐6‐chloropyridines is interpreted in terms of a cis conformation between the methyl fragment and the nitrogen ring atom. Other data, taken from the current literature, support this conclusion.
Applications of 95Mo NMR. 5—substituent effects in the 95Mo and 13C NMR spectra of benzyltricarbonyl(η5‐cyclopentadienyl)molybdenum(II) derivatives
Authors: Brownlee R. T. C. , Masters A. F. , O'Connor M. J. , Wedd A. G. , Kimlin H. A. , Cotton J. D. 
Published: May 2005

AbstractA systematic study has been made of the effects of substituent induced chemical shifts in [(η5‐C5H5)(CO)3Mo(CH2C6H4R)] compounds. Both 95Mo and 13C NMR shifts in the aromatic ring are reported. The (η5‐C5H5)(CO)3MoCH2 group is a reasonably strong resonance donor (σR° = −0.21) and weak inductive donor (σI = −0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (range c. 40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this spin 5/2 nucleus.
13C NMR spectra of phosphole–P(IV) dimers; ABX and AA′X 13C31P coupling in some derived structures
Authors: Quin Louis D. , Mesch Keith A. , Bodalski Ryszard , Pietrusiewicz K. Michal 
Published: May 2005

AbstractThe easily obtained dimers of phosphole oxides, sulfides and methiodides give 13C NMR spectra where carbons within three (sometimes four) bonds of each 31P nucleus are doublets of doublets and thus constitute X in an AMX spectrum. Most of the spectra have been completely interpreted with the aid of spectral measurements at two magnetic fields. Saturation of the double bonds in dimers of methylphosphole–P(IV) derivatives causes the 31P nuclei to have very similar chemical shifts, with Δν not adequately different from 3J(PP) to give first‐order coupling. When both 31P nuclei couple with a given 13C, a second‐order (ABX) 31C NMR spectrum is obtained. The presence of the effect is revealed by running the 13C NMR spectra at high magnetic field; J(AX)+J(BX) is constant at all fields, but spacing between the lines of the multiplet varies. The spectrum of the oxide, with Δν/J=1.44 for the 31P spectrum at 36.43 MHz, approaches first order character at 75 MHz; the methiodide spectrum (Δν/J=4.55) is second order at 15 MHz but clearly first order at 50 MHz, and the sulfide (Δν/J=5.6) is nearly first order at 15 MHz. [2 + 2]‐Photochemical intramolecular cyclization of the dimer oxides provides cage‐like structures where the 31P nuclei are chemically equivalent, but magnetically non‐equivalent, making the 13C signals have the characteristics of X in an AA′X coupling pattern.
The structure of 2‐carboxyphenyl methyl selenoxide, its sodium salt and related compounds in solution, studied by 1H, 13C and 77Se NMR
Authors: Nakanishi Warö , Ikeda Yoshitsugu , Iwamura Hiizu 
Published: May 2005

Abstract1H, 13C and 77Se NMR spectra of 2‐carboxyphenyl methyl selenoxides, 2‐carboxyphenyl phenyl selenoxides, their sodium salts and related compounds have been measured to determine their structures in solution. The 77Se NMR chemical shifts and the J(77Se, 13C) values were found to be particularly useful in distinguishing between selenuranes and selenoxides. The downfield shifts of 286‐536 and 587‐667 ppm from selenoanisoles are characteristic of the corresponding selenuranes and selenoxides, respectively. The couplings were 61‐65 and 77‐81 Hz for the selenuranes and selenoxides, respectively. The effects of salt formation on the NMR parameters are also discussed. The results show that the carboxylic acids have the cyclic selenurane structure, whereas the salts are acyclic selenoxides.
cis–trans isomerization of 2‐(4‐pyridyl)‐substituted thiazolidine‐4‐carboxylic acids: pH dependence by 1H and 13C NMR
Authors: Ponticelli Fabio , Marinello Enrico , Missale Maria Cristina 
Published: May 2005

AbstractThe presence of two diastereoisomeric thiazolidines obtained by the reaction of L‐cysteine or L‐cysteine ethyl ester and pyridoxal or pyridoxal‐5‐phosphate is demonstrated by 1H and 13CNMR spectroscopy. Fast interconversion of isomers occurs in neutral or alkaline solution.
Carbon‐13 NMR study of isoxazolopyridine systems
Authors: Chimichi Stefano , Tedeschi Piero , Camparini Alfredo , Ponticelli Fabio 
Published: May 2005

AbstractThe 13C NMR spectra of all azabenzenoid isoxazolopyridines and some of their chloro derivatives are discussed. All 13C resonances were unambiguously assigned by means of gated decoupled spectra, from which one‐bond and long‐range 13C1H coupling constants have been determined from line splittings.
Radical reactions in the co‐ordinated sphere of transition metals. XIV—spin distribution of phenoxy radicals generated from biphenyldiols
Authors: Pelikán P. , Tkáč A. , Omelka L. , Staško A. 
Published: May 2005

AbstractThe phenoxy radicals obtained from 2,2′‐ and 4,4′‐biphenyldiols show, in nonpolar solvents, symmetrization of the unpaired electron spin density on the two phenyl rings in the temperature range 290–410 K. Below 270 K the paramagnetic systems became diamagnetic. This para‐diamagnetic conversion with temperature is reversible. According to INDO calculations the symmetrization of spin density is due to the formation of dimeric phenoxy radicals. The para‐diamagnetic conversion at various temperatures is explained by the reversible conversion of the radical dimer to the quinone‐hydroquinone pair.
Calculations of some 1J(SiC) and 1J(SiF) values
Authors: Duangthai S. , Webb G. A. 
Published: May 2005

AbstractSome calculations of 1J(SiC) and 1J(SiF) are performed by self‐consistent perturbation theory employing standard INDO parameters. 1J(SiC) is dominated by the contact interaction, whereas the opposite sign for 1J(SiF) is due to a large orbital interaction. The 1J(SiC) data are satisfactorily reproduced by calculations employing an sp basis set, whereas the inclusion of silicon 3d orbitals provides a more reasonable account of 1J(SiF).
Compounds with bridgehead nitrogen: 45—the 1H NMR spectra and stereochemistry of some dimethylperhydro‐oxazolo[3,4‐a]pyridines
Authors: Crabb Trevor A. , Heywood Geoffrey C. 
Published: May 2005

AbstractThe positions of conformational equilibria in 1,5‐, 1‐6‐ and 1,8‐dimethylperhydro‐oxazolo[3,4‐a]pyridines were determined by 1H NMR spectroscopy. The cis‐(H‐5, H‐8a)‐1,6‐dimethyl‐perhydro‐oxazolo[3,4‐a]pyridine. In contrast, r‐1,t‐6,t‐8a‐1,6‐dimethylperhydro‐oxazolo[3,4‐ a]pyridine preferred the cis‐fused conformation. Three of the 1,8‐dimethylperhydro‐oxazolo[3,4‐a]pyridines adopted the trans‐fused conformations (with distortion of the system in the case of the r‐1,c‐8,c‐8a derivative) and the r‐1,c‐8,t‐8a‐1,8‐dimethyl derivative adopted the cis‐fused conformation.
Stereochemical studies of substituted 6,7‐ benzomorphan derivatives by 13C and 1H NMR spectroscopy
Authors: Casy A. F. , Ogundaini A. O. , Parfitt R. T. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of 6,7‐benzomorphan derivatives variously substituted at C‐5 and C‐9 by methyl and at C‐3 by cyano, alkyl and aralkyl groups, together with certain 3‐cyano, 3‐allyl or benzyl congeners, are reported and chemical shift data analysed in terms of the configuration of isomeric pairs and compounds isolated as single diastereoisomers. Special attention is given to the consequences of γ‐shielding interactions, the effects of the nitrogen lone‐pair orbital and anisotropic shielding by the aromatic region of the molecule. Deductions of stereochemistry are supported by 1H NMR data and the NMR features of the corresponding methiodide salts.