bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon—carbon coupling constants derived from biosynthetic studies
Authors: Horak R. Marthinus , Steyn Pieter S. , Vleggaar Robert 
Published: May 2005

AbstractThe published data up to 1984 on carbon‐carbon coupling constants derived from biosynthetic studies are presented. Nearly 1400 one‐, two‐, and three‐bond carbon‐carbon coupling constants, representing 212 compounds are arranged in three Tables. In the first Table the compounds, together with their J (CC) values, are arranged according to their biosynthetic origin. In the second Table couplings over more than one bond are collected. The one‐bond couplings are arranged in Table 3, in order of increasing magnitude in each of six categories which, in turn, are based on the formal hybridisation of the coupled carbon atoms. This method of categorisation provides direct access to a vast amount of biosynthetic information and allows the estimation of typical ranges for the various types of (C,C) coupling constants. The magnitude of the carbon‐carbon couplings is discussed in terms of factors such as the electronegativity of the substituents, ring size and stereochemical influences. In addition, the applications of carbon‐carbon coupling in biosynthetic studies, as well as the experimental methods for obtaining these values, are discussed.
The structure of thialene as studied by proton magnetic resonance in a nematic phase
Authors: Suryaprakash N. , Khetrapal C. L. , Klein R. F. X. , Horak V. 
Published: May 2005

Abstract1H NMR studies on thialene (cyclopenta[b]thiapyran) oriented in a nematic liquid crystalline phase are reported. The indirect spin‐spin and direct dipolar couplings and the chemical shifts between the protons are derived from the spectral analysis. The intra‐ring proton‐proton indirect couplings derived from the isotropic and nematic phase spectra are in agreement. The inter‐ring proton‐proton couplings, however, could only be obtained from the nematic phase spectra. The structural information extracted from the direct dipolar couplings corresponds to significant distortions in the arrangement of the protons of the six‐ and five‐membered rings from the regular hexagonal and pentagonal arrangements, respectively; the molecular geometry of the fused five‐membered ring is similar to that of the corresponding ring in azulene.
Intramolecular van der Waals interactions and 13C chemical shifts: Substituent effects in some cyclic and bicyclic systems
Authors: Li S. , Chesnut D. B. 
Published: May 2005

AbstractIn recent work, a reasonably good linear correlation was found to exist between the local van der Waals steric energy as calculated by the MM2 force field and the chemical shift of the resonant nucleus within classes of saturated aliphatic phosphines, amines, hydrocarbons and monofunctional alcohols. This study extends this work to some additional cyclic systems: 91 trans‐ and 31 cis‐decalin carbons, 57 bicyclo[2.2.1]heptane and 27 bicyclo[2.2.2]octane nuclei have been investigated and yield root‐mean‐square errors of 3.3–3.7 ppm and correlation parameters in good agreement with those found previously for other carbon species. In the more strained bicyclo systems it is found that additional class parameters must be defined. The theory is applied to a variety of α,β,γ,… ubstituents effects in cyclohexane and decalin systems, and correlated these resonant shifts under one simple, physical model.
Application of two‐dimensional NMR spectroscopy to the study of the cyclic decapeptide antamanide
Authors: Giralt Ernest , Feliz Miguel 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of antamanide were analysed by using the concerted application of two‐dimensional (2D) homocorrelated (1H1H) and heterocorrelated (13C‐1H) spectroscopy. Through these experiments it was possible to confirm the assignment of many of the 1H and 13C NMR signals of antamanide and, in addition to provide further assignments. The temperature coefficients of all the NH resonances were calculated by comparing 2D spectra obtained at different temperatures.
Concerted use of homo‐ and hetero‐nuclear 2D NMR: 13C and 1H assignment of sucrose octaacetate
Authors: Nishida Toshiaki , Enzell Curt R. , Morris Gareth A. 
Published: May 2005

AbstractThe complete assignment of the sugar and acetate 13C and 1H signals of sucrose octaacetate by homo‐ and hetero‐nuclear 2D NMR is described, using the Jeener (COSY) and relayed coherence transfer techniques and heteronuclear shift correlation via both one‐bond and long‐range couplngs.
1H and 13C NMR studies on 2‐aminofluorene derivatives with carcinogenic and mutagenic activities
Authors: Nicoletti M. , Iorio M. A. 
Published: May 2005

Abstract1H and 13C NMR spectroscopy were utilized for the identification of carcinogenic and mutagenic N‐hydroxy(acyloxy)‐2‐acetylaminofluorenes, and the inactive products derived from their thermal/enzymatic rearrangement involving N→C‐1/C‐3 migration of the hydroxy (acyloxy) group.
13C and proton nuclear magnetic resonance spectra of trans‐[arylbromobis(triethyl phosphine)palladium(II)] and related compounds. The π‐donor ability of the Ni(PEt3)2X, Pd(PEt3)2X and Pt(PEt3)2X groups
Authors: Granell Jaume , Muller Guillermo , Rocamora Mercè , Vilarrasa Jaume 
Published: May 2005

Abstract13C and proton NMR spectra of several arylpalladium and some arylnickel and arylplatinum complexes have been compared. The Ni(PEt3)2X and Pd(PEt3)2X substituents induce a paramagnetic shift of Cipso (of the phenyl ring) which is much larger than that induced by Pt(PEt3)2X. However, there are no significant differences along the Ni/Pd/Pt series for the ortho, meta and para positions. For the six compounds of general formula trans‐[ArPdBr(PEt3)2] reported here, the mean Δ(δ)C values induced on the ArH by the introduction of the PdBr(PEt3)2 substituent are found to be 26.9 (Cipso), 7.2 (Cortho), −1.1 (Cmeta), −5.5 (Cpara), −0.03 (Hortho), −0.28 (Hmeta) and −0.38 ppm (Hpara).
The use of 13C satellites in the proton NMR spectra of oriented systems for the determination of molecular structure
Authors: Suryaprakash N. , Khetrapal C. L. 
Published: May 2005

AbstractThe use of the 13C satellites in the proton NMR spectra of systems providing deceptively simple spectra is suggested and demonstrated for the determination of molecular geometry using NMR spectroscopy of oriented systems. The rα structure of phenyl isothiocyanate has thus been determined. The spectrum without the 13CH satellites does not provide sufficient independent dipolar couplings to determine the relative arrangements of protons and the order parameters.
Sequential assignments in deoxyribonucleotide tetramers by 31P/1H two‐dimensional shift correlation NMR spectroscopy
Authors: Otter Albin , Lown J. William , Kotovych George 
Published: May 2005

AbstractThe potential of two‐dimensional 31P/1H shift correlation NMR spectroscopy is demonstrated on three self‐complementary oligodeoxyribonucleotides: [d(CpGpCpG)]2, [d(ApCpGpT)]2 and [d(ApGpCpT)]2. The usefulness of this experiment for the sequential assignments of the nucleotides as a complementary technique to homonuclear shift correlation procedures (e.g. COSY) is outlined. The complete 31P assignments for all three tetramers are given, and are compared with literature data obtained by different approaches. A surprising and, as far as we are aware, previously unreported property of the 4′‐protons in the sugar phosphate backbone is described.
Carbon‐13 chemical shift assignment of some organophosphorus compounds. II—bicyclic phosphoranes bearing a chiral pentacoordinated phosphorus and a chiral carbon atom
Authors: Al‐Rawi Assim M. A. , Ayed Naceur , Osman Ayez H. 
Published: May 2005

AbstractCarbon‐13 chemical shifts and PC coupling constants of seven bicyclic phosphoranes[1‐alkyl or 1‐aryl‐2,8‐dioxa‐5‐aza‐1‐phospha(V)bicyclo[3.3.0]octanes] and their 3‐ and 6‐substituted bicyclic phosphoranes were verified using changes in the 13C chemical shifts and the J(PC) values.
Molecular structure determinations of BF3‐tetralone complexes by NMR spectroscopy
Authors: Torri J. 
Published: May 2005

AbstractThe 13C NMR shielding effects of the carbonyl‐BF3 interaction for a series of methyl‐ and methoxy‐tetralones were determined. Once the conformations of the complexes have been defined, the major shift data which can be related to charge density changes can be qualitatively discussed in terms of the transmission of the electronic properties of the CO:BF3 group. Complexation mainly causes a reorganization of the conjugated π‐system via a resonance mechanism. Delocalization of the π‐electrons towards the BF3 electron‐withdrawing group increases the carbonyl reactivity of the base, while complex stability is favoured.
13C NMR spectra of 7‐, 8‐, 9‐ and 10‐fluorobenzo[a]pyrene
Authors: Sardella D. J. , Boger E. 
Published: May 2005

AbstractThe 13C NMR spectra of 7‐, 8‐, 9‐ and 10‐fluoro‐benzo[a]pyrenes have been recorded and the chemical shifts of all protonated (and fluorine‐substituted) carbons have been assigned. The effect of fluorine on carbon shifts (and also on electron densities, which correlate reasonably well with the shifts) is confined largely to the fluorinated ring and contiguous sites, such as peri positions or carbons across bay regions. A variety of short‐ and long‐range couplings are observed, and correlations with π‐bond orders (two‐bond couplings) and ato n polarizabilities (one‐bond couplings) are observed. Long‐range coupling patterns are less obvious, but six‐bond couplings appear to correlate with atom‐atom polarizabilities, as expected for transfer of spin information through the π‐system.
13C and 1H NMR spectral studies of some piperidin‐4‐one oximes
Authors: Pandiarajan K. , Mohan R. T. Sabapathy , Hasan Misbah Ul 
Published: May 2005

Abstract13C NMR spectra have been recorded for eleven piperidin‐4‐one oximes and for seven of them 1H NMR spectra have been recorded at 270 MHz. The effect of oximation on the NMR chemical shitts is discussed. The conformations of the oximes are also discussed, based on the observed chemical shifts. Although several oximes appear to adopt a chair conformation, in the same manner as the corresponding ketones, the oximes of 3,5‐dimethyl‐2,6‐diarylpiperidin‐4‐ones with cis‐methyl groups seem to adopt an asymmetric non‐chair conformation. Analysis of the chemical shifts of cis‐2,6‐dimethylcyclohexanone oxime suggests that this compound also exists in a non‐chair conformation, and not in a chair conformation with two axial methyl groups as suggested previously.
1H and 13C NMR spectra of pentafulvalene compared with selected pentafulvenes
Authors: Escher André , Bönzli Peter , Otter Albin , Neuenschwander Markus 
Published: May 2005

AbstractThe 1H NMR spectrum of pentafulvalene has been analysed. Proton‐proton coupling constants and 13C chemical shifts are compared with those of sterically similar pentafulvenes. Pentafulvalene can be regarded as a pentafulvene with a highly localized π‐system.
Chelate ring effects in 95Mo NMR spectroscopy
Authors: Alyea Elmer C. , Somogyvari Arpad 
Published: May 2005

AbstractRing contributions (δR) to the chemical shift in 95Mo NMR spectroscopy are defined for some molybdenum(0) complexes of chelating phosphine ligands. The chelate ring effect is greatest for five‐membered rings, with the 95Mo resonances being shielded by ca 120 ppm for the ditertiary phosphine complexes. Experimental estimates of δRR(95Mo) are also reported for five‐membered rings containing nitrogen and arsenic donor ligands.
13C NMR studies of 23‐norchol‐20(22)(E)‐enoic acid derivatives
Authors: Maier Marta S. , Seldes Alicia M. , Gros Eduardo G. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of derivatives of 23‐norchol‐20(22)(E)‐enoic acids and their ethyl esters are reported.
Benzene‐induced 1H NMR shifts of flavone protons: Detection of H‐3
Authors: Vyas Ashok V. , Mulchandani Newand B. 
Published: May 2005

AbstractDeuteriated benzene‐induced shifts [Δ ppm = δ(CDCl3)–δ(C6D6)] in the 1H NMR spectra of some naturally occurring polyoxygenated flavones isolated from Ageratum conyzoides and Eupatorium odoratum have been studied. The downfield shift of the pyrone ring proton H‐3, particularly in B‐ring methoxylated flavones, is significant; as it is in the opposite direction to that of an aromatic proton it could be of diagnostic value in structural elucidation. The benzene‐induced shifts of all the other protons have also been studied.
Nitrogen‐15 nuclear magnetic resonance studies of hydrogen bonding and proton transfer in some pyridine trifluoroacetates in dichloromethane
Authors: Dega‐Szafran Z. , Szafran M. , Stefaniak L. , Brevard C. , Bourdonneau M. 
Published: May 2005

AbstractThe 15N NMR chemical shifts of ten substituted pyridines (B) and their complexes with trifluoroacetic acid (AHB) were measured at the natural abundance level in dichloromethane. The plot of the relative chemical shifts [Δδ(15N)δ(AHB)δ(B)] against ΔpKa gives a titration curve which reflects a protometric equilibrium AH…B⇌A−…HB+. These data were used to determine the constants of the overall proton transfer reaction (Kexp). A linear relationship holds between log Kexp and ΔpKa. Δδ(15N) values can be treated as a good hydrogen bond parameter.
1H NMR study of Eu(fod)3–macrocyclic lactone systems
Authors: Cazaux L. , Picard C. , Tisnes P. 
Published: May 2005

AbstractThe effect of Eu(fod)3 on some 12–30‐membered macrocyclic lactones containing various basic sites was investigated in CDCl3 solution using 1H NMR spectroscopy. Apparent complexation constants Kc, and lanthanide‐induced shifts of the complexes were determined for an assumed 1:1 stoichiometry. In these macrocycles, the participation of the binding sites depends not only on their nature, but also on the ring size and on the conformational behaviour of the macrocycles. On the other hand, the equilibrium constant data clearly indicate that the ring size is the dominating factor in the stability of the Eu(fod)3–lactone system.
Comparison of the thiocarbonyl13C NMR resonances of N‐phenylthioureas, N‐phenyl thiocarbamates and N‐phenyl dithiocarbamates
Authors: Ares Jeffrey J. , Urchek Thomas G. , Palmer Charles W. , Miller Duane D. 
Published: May 2005

Abstract13C NMR spectra of N‐phenylthioureas, N‐phenyl thiocarbamates and N‐phenyl dithiocarbamates of the ethyl and n‐butyl type are compared. Significant differences are observed in the chemical shift of the thiocarbonyl carbon, which do not parallel the electronegativity of the bonded heteroatom.
Mercuration effects on nucleoside chemical shifts: 15N and 13C NMR studies of methylmercury(II) ion addition to cytidine‐3′‐monophosphate and guanosine‐5′‐monophosphate
Authors: Buchanan G. W. , Bell M.‐J. 
Published: May 2005

AbstractMethylmercuration of cytidine‐3′‐monophosphate is shown to occur at the N‐3 site, resulting in a substantial upfield shift in the 15N resonance of this nitrogen. For guanosine‐5′‐monophosphate the 15N NMR data show N‐1 to be the site of complexation of CH3Hg+ at pH 8. The large downfield shift observed for N‐1 as a result of this binding is explained in terms of a concomitant deprotonation phenomenon. Changes in 13C NMR chemical shifts on methylmercuration are less pronounced, but consistent with these binding sites.
Solvation of alkylaromatic hydrocarbons towards a paramagnetic relaxation reagent, tris(acetylacetonato)chromium(III)
Authors: Holak Tadeusz A. , Aksnes Dagfinn W. , Grahn Hans , Edlund Ulf 
Published: May 2005

AbstractA 13C electron–nuclear spin–lattice relaxation study showed that the interaction between alkyl‐substituted aromatics and a paramagnetic relaxation reagent, tris(acetylacetonato)chromium(III), is purely electrostatic, i.e. of a dipole–dipole or dipole–induced dipole type. Except for aromatics having bulky alkyl groups, the preferred chelate position is close to the positive end of the dipole, i.e. close to the α‐position. However, the major electron–nuclear mechanism is non‐specific, and the relaxation rate is mainly controlled by the mutual translational/rotational diffusion of the two species. Paramagnetic shifts induced on addition of Cr(acac)3 support the suggested interaction mechanism.
An application of nJ(CH2,H) and 5J(OH,H) long‐range couplings in the conformational analysis of 2‐hydroxybenzyl methyl ether in various solvents. Computational strategies for spectral analysis and determination of association thermodynamic parameters
Authors: Laatikainen Reino 
Published: May 2005

Abstract1H NMF spectra of 2‐hydroxy‐ and 2‐methoxy‐benzyl methy1 ethers were measured in various solvents and solvent mixtures. Precise nJ(CH2,H), where n = 4, 5 or 6, and 5J(OH,H) long‐range couplings were applied to the characterization of the conformational behaviour of the systems. Qualitatively, the compounds appear to exist in two Principal conformations: in a closed syn with an internal hydrogen‐bonded form, and/or in an open anti conformation with the CH2OR group tilting fairly freely in the benzene plane. The open form is favoured in acetone and dioxane. The computational strategies used in the spectral analysis of the long‐range couplings and in the analysis of the solvent‐solute association equilibria are described.
Thermal cycloaddition reaction of xanthene‐9‐thione with allenes: An ESR study
Authors: Kamphuis J. , Bos H. J. T. , Huizer A. H. 
Published: May 2005

AbstractDuring the parallel (2 + 2)‐ and (4 + 2)‐cycloaddition reactions of aromatic thiones such as xanthene‐9‐thione with substituted allenes XCHCCH2 (X = OR, SR, NMe2, Ph), a strong ESR signal is observed. This signal is associated with the (4 + 2)‐cycloaddition reaction, affording thiopyran derivatives 3,11b‐dihydro‐2‐(X‐methylene)‐2H‐thiopyrano[4,3,2‐kl]xanthene F or 3,11b‐dihydro‐3X‐2‐methylene‐2H‐thiopyrano[4,3,2‐kl]xanthene E. Computer analyses of this signal made possible its identification as emanating from a 9‐xanthenyl radical substituted at the 1‐ and 9‐positions. The type of xanthenyl radical that is formed in the thermal reaction E rad or F rad depends on the nature of the substituent X at the allenic system H2CCCHX. This investigation shows that where X = Ph and NMe2, xanthenyl radicals of structure E rad are produced, and where X = O‐t‐Bu and S‐t‐Bu xanthenyl radicals of structure F rad are produced. It is striking that this production is so selective.On irradiation (λ>254nm), the production of xanthenyl radicals is enhanced. The conformation of xanthenyl radicals E rad and the role of E rad and F rad in the formation of addition products E and F are discussed.
A new approach utilizing high‐resolution proton NMR in structural analysis of intercalation complexes of natural DNA
Authors: Chandrasekaran S. , Kusuma S. , Boykin David W. , Wilson W. David 
Published: May 2005

AbstractProtons on the antimalarial intercalator quinacrine and a substituted phenanthrene intercalator were monitored on titration with sonicated DNA. The titrations were carried out below the DNA Tm but at a temperature, ionic strength, and intercalator concentration sufficient to give fast exchange conditions and a minimum of dimerization of the planar aromatic intercalators. Line widths were kept within reasonable limits by using sonicated DNA, high temperature, fast exchange conditions and an excess of intercalator over DNA binding sites.Proton assignments were made using analysis of chemical shifts, coupling patterns, NOE and 2D methods. 2D COSY experiments on DNA‐intercalator complexes were performed to assist in assigning protons for the bound intercalator. Line broadening with quinacrine is more severe than with the phenanthrene, and the acridine essentially represents the limit of the NMR titration method. The phenanthrene intercalator, on the other hand, illustrates the power of the method, particularly when analyzing a series of compounds. Using chemical shift changes of the phenanthrene on titration with DNA and space filling molecular modeling studies, we have been able to propose a general structure for the phenanthrene intercalation complex.
13C chemical shifts and 13C13C coupling constants of some alkyl(aryl)sulphonates
Authors: Millot C. , Brondeau J. , Canet D. 
Published: May 2005

AbstractThe 13C resonances of sodium n‐octylsulphonate, octylbenzene‐sulphonate and 4‐dodecylbenzenesulphonate in aqueous solutions have been assigned, either physically by selective detection of their 13C satellites, or by comparison. Some one‐bond carbon‐carbon couplings have been accurately determined.
Long‐range deuterium isotope effects on 1H chemical shifts in some simple organometallic compounds
Authors: Wei Yong‐Cheng , Wells Peter R. , Lambert Lynette K. 
Published: May 2005

AbstractProton NMR spectra are reported for chlorotrimethylstannane, tetramethylstannane, tetramethylplumbane and dimethylmercury containing various combinations of CH3 and CD3 groups. Additive long‐range isotope effects on chemical shifts, 4ΔH(D), are observed to result in increased shielding of essentially the same magnitude in each case. There appears to be no significant isotope effect on the 2J coupling constant.
1H and 13C chemical shift assignments of homoisoflavanones
Authors: Adinolfi Matteo , Lanzetta Rosa , Laonigro Guglielmo , Parrilli Michelangelo , Breitmaier Eberhard 
Published: May 2005

Abstract13C chemical shifts of various homoisoflavanones were assigned, mainly on the basis of long‐range heteronuclear 2D NMR shift correlation experiments and of long‐range proton‐carbon coupling constants. In addition, 1H chemical shift data are reported. Some general relationships between substitution patterns and nuclear shielding, useful for the identification of naturally occurring homoisoflavanones, are discussed.
35Cl NQR investigations on crystalline α,α′‐dichloro‐o‐xylene
Authors: Venkatacharyulu P. , Prasad N. V. L. N. , Rao C. H. Bhaskar , Premaswarup D. 
Published: May 2005

AbstractThe Zeeman spectrum of the 35Cl NQR line in a cylindrical single crystal of α,α′‐dichloro‐o‐xylene was recorded at room temperature and analysed to obtain information regarding the nature of the crystalline unit cell. The crystal system is determined from the analysis. The two observed loci are due to the two chlorines in a single molecule, and all the benzene rings are parallel to one another whereas the two CCl bonds are inclined to one another at an angle of 102°. The absence of a cleavage plane may be due to the out‐of‐plane CCl and CH bonds in the chloromethyl groups. The ionic, single bond and double bond characters are in the ratio 28.54:70.64:0.82.
Analysis of unusual 13C77Se couplings in the 13C NMR spectra of selenoimidates
Authors: Contreras R. H. , de Azúa M. C. Ruíz , Giribet C. G. 
Published: May 2005

AbstractThe difference between cis and trans 13C77Se couplings reported recently for selenoimidates is analyzed using the IPPP‐INDO method, which allows a study of the stereochemical behaviour of differently transmitted components of electron‐mediated spin‐spin coupling constants. It is concluded that a large through‐space transmission of the Fermi contact term takes place for the cis 13C77Se coupling via an Se‐electron‐pair…HC bond coupling pathway. The influence of the steric compression of the Se‐electron pairs on the one‐bond 13C77Se couplings is also discussed.