bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisochrony of the O‐methylene protons of the C‐2‐ethyl ester function in triethyl meso, cis‐1,3‐dimethylcyclohexane‐1,2,3‐tricarboxylate—Atropisomerism of an ester group
Authors: Balasubrahmanyam S. N. , Bharati S. Narasimha 
Published: May 2005

AbstractThe methylene protons of the ethyl ester function at C‐2 in triethyl meso, cis‐1,3‐dimethylcyclohexane‐1,2,3‐tricarboxylate (A) are anisochronous, despite the apparent symmetry of structure A. The necessary diastereotopy is thought to be engendered by the central ester being stabilized in a rotamerization in which the O:C·O plane is held parallel to the general plane of the 6‐membered ring while fast exchanges take place among rotamers about the alkyl–oxygen bond; other rotamers about the ester axis are thought to encounter high order repulsive steric/polar interactions with the flanking ester functions and C‐methyl groups. Evidence for the axial orientation of the C‐1 and C‐2 ester functions in A, based on comparisons of its 1H NMR spectral characteristics with those of its RS‐cis, trans and meso, trans analogues, is presented. The role of ion‐pairing in the stereoselectivity of methylation of precursor enolates, leading to the formation of these three systems, is briefly discussed. A comment on the appropriateness, or otherwise, of drawing conformational conclusions from the magnitudes of the anisochrony in comparable systems is included. Triester A is thought to be the first instance where atropisomerism about an sp3sp2 bond involving an ordinary ester function has been detected employing a prochiral sensor group.
Automatic assignment of 13C NMR spectra based on the chemical shift/charge density relationship
Authors: Bangov Ivan P. 
Published: May 2005

AbstractAn approach for the automatic assignment of 13C spectra, based on the chemical shift/charge density relationship, is suggested. All permutations of spectral signals are computer‐generated, and for every permutation a least squares adjustment is carried out. The permutation presenting the highest correlation coefficient, or the lowest Hamilton's agreement factor, is considered to be correct. The application is exemplified by the 13C chemical shifts of a series of aromatic compounds. It is shown that more reliable assignment is achieved if the considered permutations are restricted by taking intoaccount the signal multiplicity.
Rapid injection NMR: A simple technique for the observation of reactive intermediates
Authors: McGarrity John F. , Prodolliet Jacques , Smyth Timothy 
Published: May 2005

AbstractA system has been designed for the NMR observation (at 60 MHz) of unstable intermediates, with half‐lives of 100 ms, at concentration levels above 10−2 M. Rapid mixing can be achieved in less than 40 ms and a series of eight spectra acquired in less than 1.08 s. Low temperature operation is straightforward. Reactive intermediates involved in the reaction of methylamine with 2,4,6,‐trinitroanisole and the acid‐catalysed hydrolysis of 1,1‐diethoxy‐2,3‐diphenylcycloprop‐2‐ene were identified, and in a kinetic application, the rate of hydrolysis of trimethyloxonium tetrafluoroborate was measured.
The paramagnetic species produced in the reactions of organometallic compounds XIII—the anion radicals of carboxylates
Authors: Staško A. , Malik Ľ. , Mat'ašova E. , Tkáč A. 
Published: May 2005

AbstractIn the reactions of meta‐ and para‐alkyl substituted benzoic acids with aryl Grignard reagents, in tetrahydrofuran solutions and in the presence of nickel salts, the ESR spectra of the anion radicals of carboxylates derived from the benzoic acids were observed which represent the intermediates in the formation of ketyl radicals.
New triterpenes from Swietenia mahagoni. IV—the 13C NMR spectra of cycloswietenol, 30‐norcycloswietenol and isocycloswietenol
Authors: Lakshminarayana V. , Murty Y. L. N. , Row L. R. 
Published: May 2005

Abstract13C NMR spectral data of cycloswietenol and 30‐norcycloswietenol from Swietenia mahagoni and the rearranged product, isocycloswietenol, are presented and their specific structural features discussed.
Application of principal component analysis to 13C NMR shifts of chalcones and their thiophene and furan analogues: A useful tool for the shift assignment and for the study of substituent effects
Authors: Musumarra Giuseppe , Wold Svante , Gronowitz Salo 
Published: May 2005

Abstract13C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross‐validation. The first component corresponds to ordinary σpara values, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationships.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Chemical shifts of methyl substituted cis‐decahydroquinolines
Authors: Vierhapper Friedrich W. , Furst George T. , Lichter Robert L. 
Published: May 2005

Abstract15N Chemical shifts of cis‐decahydroquinoline, N‐methyl‐cis‐decahydroquinoline, and of 19 methyl substituted NH‐ and NCH3‐cis‐decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature 13C NMR spectroscopy.
Carbon‐13 NMR spectra of some novel migrated hopanes and 21α‐H hopanes
Authors: Patra Amarendra , Mitra Alok K. , Chatterjee Tapan K. , Barua A. K. 
Published: May 2005

AbstractThe carbon‐13 NMR spectra of the novel rearranged hopanes, spergulagenin‐A and related triterpenoids, and 21α‐Hopanes, mollugogenol‐A, mollugogenol‐G diacetate and related compounds, were recorded. Their analyses were aided by the chemical shifts of some model compounds and by the change in chemical shifts produced on change of substituents/s.
1H and 31P NMR studies of rotational isomerism in phosphorus analogues of aspartic acid, 3‐amino‐3‐phosphonatopropionic and 3‐amino‐3‐(methylphosphinato) propionic acids
Authors: Siatecki Zdzisław , Kozłowski Henryk 
Published: May 2005

AbstractBy the use of the 1H1H and 1H31P coupling constants in two analogues of aspartic acid i.e. 3‐amino‐3‐phosphonatopropionic and 3‐amino‐3‐(methylphosphinato) propionic acids, it was shown that the six parameter formulation for the evaluation of mole fractions of three staggered ethanic rotamers is not necessarily better than the two parameter formulation in this system. The results allowed the recommendation of the following values for the two vicinal proton parameters i.e. J(HH)g=2.3, J(HH)t=13.9 and for the two vicinal proton‐phosphorus parameters i.e. J(HP)g=4.2, J(HP)t=33.0 Hz.
14N nuclear quadrupole resonance in N‐acetyl amino acids
Authors: Sadiq G. F. , Greenbaum S. G. , Bray P. J. 
Published: May 2005

Abstract14N Nuclear quadrupole resonance (NQR) spectra of several N‐acetyl amino acids and related compounds are reported and analyzed within the framework of the Townes and Dailey theory. The inductive effect of the chloroacetyl group on the nitrogen is discussed. A positive correlation between the π‐σNC electron density at the nitrogen and the Taft inductive parameter σ* is observed, suggesting that the nitrogen π‐charge density in the N‐acetyl amino acids does not vary appreciably. NQR data for hippuric acid are compared to the 14N quadrupole parameters extracted from ENDOR data reported for X‐irradiated hippuric acid.
14N nuclear quadrupole resonance in carbazoles
Authors: Kim N. S. , Bray P. J. 
Published: May 2005

AbstractNitrogen‐14 nuclear quadrupole resonance frequencies at 77 K are reported for a series of carbazole compounds including N‐vinylcarbazole. Differences in charge distribution between pyrrole and carbazole are explained on the basis of delocalization of pi electrons. Effects of the aldehyde and vinyl groups on charge distribution are discussed. Sigma bond polarization between the pyrrole nitrogen and the nitroso nitrogen toward the pyrrole nitrogen exists in N‐nitrosocarbazole.
Values and signs of 13C, 1H spin‐spin coupling constants in 1,6,6aλ4‐trithiapentalene and 1,6‐dioxa‐6aλ 4‐thiapentalene
Authors: Bjorholm T. , Jacobsen J. P. 
Published: May 2005

AbstractThe values and signs of 13C, 1H spin‐spin coupling constants in 1,6,6aλ4‐trithiapentalene and 1,6‐dioxa‐6aλ4‐thiapentalene have been re‐investigated. The contributions from second order effects in the spectra have been included in an iterative spectral analysis. The values found deviate significantly from the values found earlier by first order analysis. The signs of the spin‐spin coupling constants have been established by the use of the SPT technique.
The isotropic hyperfine interaction in some aliphatic polyamine copper II complexes
Authors: Pisipati V. G. K. M. , Satyanandam G. , Rao N. V. S. 
Published: May 2005

AbstractESR and optical absorption studies have been carried out on bis[N‐(2‐hydroxyethyl)ethylenediamine] copper II‐chloride, ‐bromide, ‐nitrate, ‐sulphate, bis(N‐methylethylenediamine) copper II thiocyanate and bis(N,N′‐dimethylethylenediamine) copper II thiocyanate, in non‐interacting solvents at room and liquid nitrogen temperatures. The molecular orbital coefficients are estimated assuming axial symmetry and indicate that the in‐plane π bond is as strong as the σ bond. The consistency in the value of the χ parameter, which is proportional to the hyperfine constants, indicates that it is quite independent of the ligand substitution and depends upon the immediate environment of the copper II ion.
13C NMR investigation of some hetero‐ring substituted 2‐ and 4‐quinolone systems
Authors: Coppola G. M. , Kahle A. D. , Shapiro M. J. 
Published: May 2005

AbstractA series of 2‐ and 4‐quinolones substituted in the hetero‐ring have been evaluated using 13C NMR techniques. Substituent effects are discussed as an aid to evaluation of potential tautomerization in the 2‐quinolone systems. The observed substituent shifts for systems having a hydroxy function at the 4‐position in the 2‐quinolones can be explained without implementing the tautomerism to a 4‐quinolone.
Conformational analysis XX—13C NMR studies of saturated heterocycles 5—substituent effects on the 13C chemical shifts of methyl substituted 1,3‐dithiolanes
Authors: Pihlaja Kalevi , Eskonmaa Mauri , Keskinen Raimo , Nikkilä Alpo , Nurmi Timo 
Published: May 2005

AbstractThe 13C NMR chemical shifts for 1,3‐dithiolane and 13 methyl substituted derivatives are reported. Substituent effects are derived and compared with those for cyclopentanes and 1,3‐dioxolanes. The magnitude and variety of the substituent effects are best explained with the aid of a half‐chair conformation where the S‐1C‐2S‐3 plane passes between C‐4 and C‐5.
The reaction between trans‐2‐alkylaminocycloalkanols and formaldehyde
Authors: Barkworth Peter M. R. , Crabb Trevor A. 
Published: May 2005

Abstracttrans‐2‐Alkylaminocyclohexanols and trans‐2‐alkylaminocycloheptanols condense with formaldehyde to give perhydrocycloalkano[d][1,3]oxazoles, whereas trans‐2‐alkylaminocyclopentanols give rise to perhydrocyclopentano[f][1,3,5]dioxazepines. The two types of ring systems are characterized by differing proton‐proton geminal coupling constants and 13C NMR parameters.
15N chemical shifts as a conformational probe in enaminones A variable temperature study at natural isotope abundance
Authors: Kozerski L. , von Philipsborn W. 
Published: May 2005

AbstractThe high sensitivity of 15N shielding to the displacement of the lone pair electrons makes it a useful conformational probe for remote parts of a conjugated molecule. Thus, the chemical shifts are observed for different rotamers of enaminones in the slow exchange limit. The interpretation of the 15N chemical shifts in terms of the non‐planarity of the E, s‐E rotamers is in accord with 13C chemical shifts and 1J(CH) coupling constants.
Correlation of para substituent carbon‐13 chemical shifts in aromatic compounds using polar (inductive) and resonance constants which are identical for aliphatic and aromatic compounds
Authors: Afanas'ev I. B. , Trojanker V. L. 
Published: May 2005

AbstractA correlation of para substituted 13C chemical shifts in aromatic compounds with substituent polar (inductive) and resonance constants σ* and σr of aliphatic compounds has been studied. It has been shown that the precision of the correlations obtained corresponds to that of the Swain‐Lupton and Taft two‐parameter equations, but the correlation equation used in this work seems to permit a more exact separation of the substituent effects of aromatic compounds into inductive and resonance contributions. Thus, σ* and σr substituent constants are universal parameters which can be used in a correlation analysis of the properties of both aliphatic and aromatic compounds.
The NMR spectra of the porphyrins. 17—Metalloporphyrins as diamagnetic shift reagents, structural and specificity studies
Authors: Abraham Raymond J. , Bedford Geoffrey R. , Wright Brian 
Published: May 2005

AbstractThe nature of the metalloporphyrin‐ligand complexes produced by zinc, magnesium and cobalt porphyrins with basic ligands has been investigated using the diamagnetic ring current shifts of the porphyrin on the ligand protons. The metal to nitrogen bond lengths in some metallo‐meso‐tetraphenylporphyrin (pyridine) complexes have been determined and compared with the data of the crystalline complexes. The geometry of the Zn meso‐tetraphenylporphyrin complexes with 2‐picoline, quinoline and isoquinoline has been investigated. Steric interactions between the ligand and the porphyrin in 2‐picoline and quinoline produce a dramatic increase in the ZnN bond length when compared to the unstrained analogues pyridine and isoquinoline. This large increase is associated with comparatively minor angle distortions in the complex. The specificity of the Zn meso‐tetraphenylporphyrin complexation shifts has been determined for a range of benzyl and butyl compounds. The complexation shift is linearly related to the basicity of the ligand for a wide range of basicities.
15N chemical shifts of a number of polyazaindenes: Correlation with charge separated resonance contributing structures
Authors: Paudler William W. , Sheets Roger M. , Goodson B. 
Published: May 2005

AbstractThe 15N chemical shifts of a number of polyazaindenes have been determined, and have been correlated with the degree of contribution to the ground state of those resonance structures which place a partial positive charge on the bridge‐head nitrogen.
17O nuclear magnetic resonance studies of some enriched amino acids
Authors: Hunston Roger , Gerothanassis Ioannis P. , Lauterwein Jürgen 
Published: May 2005

AbstractThe 17O NMR chemical shifts of five enriched amino acids have been measured under strictly controlled conditions of concentration, ionic strength, pH and temperature. The α, β and α, γ carboxyl resonances of aspartic and glutamic acid, respectively, have been resolved. Line widths were examined as a function of solution viscosity.
13C NMR spectra of wedeloside and related kaurenoid derivatives
Authors: Lewis I. A. S. , MacLeod J. K. 
Published: May 2005

AbstractThe 13C NMR spectra of the diterpenoid aminoglycoside wedeloside and certain of its derivatives, representatives of a new kaurenoid series, have been assigned. Shift calculations and labelling experiments have established a general substituent additivity relationship for chemical shifts in kaur‐16‐enes which allowed the reassignment of certain 13C resonances in the previously reported spectra of other kaur‐16‐enes.
DNA fragment conformations. I—methods for the assignment of DNA fragment proton resonances. 1H NMR spectra of dApTpGpT and dApCpApTpGpT
Authors: Tran‐Dinh S. , Neumann J. M. , Huynh‐Dinh T. , Igolen J. , Kan S. K. 
Published: May 2005

AbstractA general method for the assignment of DNA fragment proton resonances, especially for the sugar protons, has been presented and used to interpret the 400 MHz proton spectra of dApTpGpT and dApCpApTpGpT in neutral aqueous solution. Only fine splittings of about 3 Hz are observed in the H‐2″ resonances, and the total splitting is larger for the H‐2′ (≈29 Hz) than for the H‐2″ (22–23 Hz) multiplets. The purine and pyrimidine resonances can be distinguished on the basis of the H‐2″ and H‐2″ chemical shifts. The resonances of the H‐2′ and H‐2″ protons (above and below the sugar plane, respectively) of dA and dG exhibit chemical shifts of 2.65—2.80 ppm, while those of dC and dT residues are located at higher fields between 1.95 and 2.40 ppm. At high temperature (≥60°C), δH‐2′>YδH‐2″ for the purine family, while δH‐2′ « δH‐2″ in the case of the pyrimidine family. Except for the terminal residue, the H‐3′ resonances of dA and dG are located at lower fields compared with those of the dC and dT residues. The same is true for the H‐4′ resonances. In general δA1′>δG1′ and in the case of self complementary duplexes the H‐1′ and H‐2′ chemical shift variations versus temperature are found to be larger for the dC than for the dT residues.
NMR study on trapping techniques to deduce the conformations of 1‐alkyl‐3‐ hydroxypiperidines
Authors: Van Luppen J. J. , Lepoivre J. A. , Dommisse R. A. , Alderweireldt F. C. 
Published: May 2005

AbstractThe conformational equilibrium of 1‐alkyl‐3‐hydroxypiperidines in n‐heptane and aqueous solution is investigated. Several methods, e.g. IR and NMR spectroscopy, are discussed. The conformation trapping in D2SO4‐D2O mixtures, and subsequent analysis of the 1H and 13C NMR spectra, is proven to be the most reliable method. In an apolar solvent the conformation with an axial hydroxyl group is always dominant (69%). In aqueous solution the same conformation predominates in the protonated form (56%, pH<5), while only 43% of this conformation is present in the free base (pH∼11). A detailed 13C NMR study is described of 1‐isopropyl‐3‐hydroxypiperidine in aqueous solution at pH between 2 and 11.
Studies in sulphur heterocyles. 2—The 13C NMR spectra of thienocoumarins
Authors: Brown Norman M. D. , De Asish , Brunskill John S. A. , Jeffrey Howard 
Published: May 2005

Abstract13C NMR spectra of 3‐ substituted thieno[2,3‐h][1]benzopyran‐2‐ones and 8‐substituted thieno[3,2‐f]‐[1]benzopyran‐7‐ones are reported and the substituent dependence of certain 13C chemical shifts is noted.
19F NMR of five polyfluoronaphthalenes. Inter‐ring FF coupling constants
Authors: Matthews R. S. 
Published: May 2005

AbstractAnalyses of the 19F and 1H spectra of 1,2,3,4,5‐pentafluoro‐, 1‐bromo‐4,5,6,7,8‐pentafluoro‐, 1,2,3,4,5,6‐hexafluoro‐, and 1‐bromo‐3,4,5,6,7,8‐hexafluoro‐naphthalene are presented, and it is observed that the Fermi contact mechanism does not, simply, account for the long range couplings. Calculations of the carbon‐carbon polarizability part of the Fermi contact term do, however, imply that inter‐ring F,F couplings should be almost constant from difluoro‐ to heptafluoro‐naphthalene. Within the limits of this study, the inter‐ring F,F couplings, excluding peri F,F couplings, do not vary substantially. The steric effect of substituting an α‐hydrogen with bromine, at a peri position and adjacent to fluorine, is to increase the F,F coupling at the opposed peri position by 20 Hz, an unusually high increase in J(FF)peri.
Carbon‐13 spectral studies of some chalcones and flavanones
Authors: Patra Amarendra , Mitra Alok K. , Bhattacharyya Anjan , Adityachaudhury N. 
Published: May 2005

AbstractCarbon‐13 signal assignments of 2′,4′‐dihydroxychalcone, flemichapparin, pashanone, isodidymocarpin, pedicellin, pedicinin, methylpedicinin, didymocarpin‐A and the corresponding quinoflavanone dehydrodidymocarpin‐A are reported.
13C NMR spectra of thieno[2,3‐b][1,5]benzodiazepine neuroleptics
Authors: Rackham David M. , Morgan Sarah E. 
Published: May 2005

AbstractThe 13C NMR spectra of five thieno[2,3‐b][1,5]benzodiazepines and two related benzodiazepinones have been recorded at 22.64 MHz using broad band and off‐resonance proton decoupling techniques. Spectral interpretation is facilitated by the presence of one (or more) fluorine substituents in the benzo‐ring.
Dynamics of 2‐pyrrolidone, δ‐valerolactam and ϵ‐caprolactam: Nuclear magnetic relaxation of carbon‐13 and nitrogen‐15
Authors: Marchal J. P. , Brondeau J. , Canet D. 
Published: May 2005

AbstractThe molecular dynamics and the association of 2‐pyrrolidone, δ‐valerolactam and ϵ‐caprolactam in H2O and CCI4 solutions have been investigated by 13C nuclear magnetic relaxation. With the aim of unambiguously establishing 13C assignments the following parameters have been measured: carbon chemical shifts, one‐bond carbon–proton coupling constants and one bond carbon–carbon coupling constants. In the particular case of 2‐pyrrolidone, the 13C relaxation times do not provide enough information in order to study in detail the dynamics of the molecule. 15N Relaxation for the neat liquid has proved to be a valuable complement for totally analysing the anisotropic motion of this lactam.
Hydrolysis of γ‐[1‐methyl‐5‐bis(β‐chloroethyl) amino‐2‐benzimidazolyl]butyric acid. Studied by 1H NMR
Authors: Klose G. , Augsten K. , Barth A. , Samek Z. 
Published: May 2005

AbstractHigh resolution 1H NMR is applied to the study of hydrolysis and equilibria in the complex system of γ‐[1‐methyl‐5‐bis(β‐chloroethyl)amino‐2‐benzimidazolyl]butyric acid and D2O. Kinetic data for the individual hydrolytic steps are obtained for the first time. The hydrolytic reactions are pseudo first order. The differences in the activation energies of the two hydrolysis steps are accounted for by different intermediates. Furthermore, equilibrium constants for the deuteration of the N mustard group in the individual products are quantitatively estimated. They show an increase of the basicity of N mustard with hydrolysis. The applicability of the 1H NMR method is restricted to a pD range of 0.5–4.
Computer supported structure elucidation of polymethoxy‐ and polyacetoxyxanthones. V—13C NMR spectroscopy of substituted xanthones
Authors: Frahm A. W. , Hambloch H. 
Published: May 2005

AbstractA procedure for developing 13C NMR chemical shift additivity rules for all 136 polymethoxyxanthones and all 136 polyacetoxyxanthones, based on multiple linear regression analysis, is reported. The influence of steric interactions between the substituents on the chemical shifts of the carbon atoms in the xanthone ring system is discussed and included in the calculations of the additivity rules for the polymethoxyxanthones. The derived chemical shift increments are implemented into the computer program SEOX 1. The extended program, SEOX 2, allows an automated structure elucidation of polyhydroxy‐, polymethoxy‐ and polyacet‐oxyxanthones. The increments are tested using the leave‐one‐out method in conjunction with SEOX 2, and have been found to be very suitable for this purpose.
13C and 77Se NMR spectra of thienoisoselenazoles, selenoloisothiazoles, selenoloisoselenazoles and thienoisothiazoles
Authors: Onyamboko N. V. , Renson M. , Chapelle S. , Granger P. 
Published: May 2005

AbstractThe 13C and 77Se NMR spectra of eight new unsubstituted biheterocycles containing a thiophene or selenophene ring condensed with an isothiazole or isoselenazole ring were recorded. The assignments of the 13C signals were made by the examination of chemical shifts, 1J(CH) coupling constants and, for the quaternary carbons, on the basis of 1J(C, 77Se) coupling constants. The results are compared and discussed.