bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C, 13C coupling constants in phenyl substituted ethylene, naphthalene, phenanthrene and cyclopentadienone. Dependence on dihedral angles. Determination of signs by the symmetrical double labelling (SDL) method. IV
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractCarbon‐13, carbon‐13 coupling constants and carbon‐13 chemical shifts have been measured in a series of phenyl substituted ethylenes and aromatics all doubly labelled with 13C at the olefinic positions (α,β‐) or at neighbouring aromatic positions, tetraphenylcyclopentadienone labelled at the 3,4‐positions, and dichlorodiphenylmethane labelled at the α‐carbon. Signs of coupling constants were determined by the symmetrical double labelling (SDL) method. Coupling constants over as many as five bonds are reported. Two‐bond couplings between carbons in the aromatic skeleton belong to different classes according to the nature of the coupling path. The magnitudes of three‐bond coupling constants between such carbons correlate linearly with π‐bond orders and a separation of the δ‐ and π‐contributions is evident. The three‐bond couplings between the 2‐position in a phenyl substituent and the olefinic β‐position or a corresponding aromatic position depend on the out‐of‐plane twist of the phenyl ring and may lead to information about the twist angle. Contrary to findings with aromatic carbonyl compounds two‐ and three‐bond couplings to the α‐carbon in the present compounds are fairly constant. The reported data suggest that the signs of coupling constants over more than two bonds alternate in aromatic systems. Carbon‐13, carbon‐13 coupling constants in naphthalene have been calculated by the INDO‐SOS method.
13C, 13C coupling constants in anthracene, 9,10‐dihydroanthracene and phthalic acid derivatives. Determination of signs by the symmetrical double labelling (SDL) method V
Authors: Hansen P. E. , Berg A. 
Published: May 2005

AbstractCarbon‐13, carbon‐13 one‐bound and long‐range coupling constants are determined for anthracene and 9,10‐dihydroanthracene labelled in the 9,10‐positions, and for thiophthalic anhydride and phthalimide, labelled in both carbonyl groups. Relative signs are determined by the SDL method. Signs in naphthalene, anthracene and pyrene derivatives are discussed. The general trends observed in many aromatic compounds, 3J|>|2J|>|4J| and 2J positive, 3J positive, 4J negative are mostly confirmed. However, evidence suggests that two‐bond couplings between carbon atoms in the same ring in aromatic hydrocarbons are negative.
Preferential protonation and methylation at the nitrogen atoms of N,N‐dimethylamino derivatives of pyridine
Authors: Barbieri Giorgio , Benassi Rois , Grandi Romano , Pagnoni Ugo Maria , Taddei Ferdinando 
Published: May 2005

AbstractThe relative reactivity toward protonation and methylation of the two nitrogen atoms in N,N‐dimethylaminopyridines has been examined by 1H NMR. The ring position of the dimethylamino group has no influence on protonation, which occurs in all the derivatives at the heterocyclic nitrogen. The N‐methylation reaction does not follow a homogeneous behaviour, occurring at the exocyclic nitrogen in the 2‐substituted dimethylamino derivative. The electronic characteristics of the molecules, determined by MO calculations at a semi‐empirical level, indicate that both protonation and methylation should occur at the heterocyclic nitrogen; the calculated relative stabilites, however, of the N‐protonated and N‐methylated forms are in full agreement with the experimental results, and it appears that the anomalous behaviour of 2‐dimethylaminopyridine in the N‐methylation reaction is caused by steric factors.
Carbon‐13 NMR spectra of some 4‐ and 5‐substituted pyrimidines
Authors: Cheeseman Gordon W. H. , Turner Christopher J. , Brown Desmond J. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts and carbon‐proton coupling constants for nine 4‐substituted and six 5‐substituted pyrimidines are reported. The carbon chemical shifts are correlated with π‐electron densities. Carbon‐proton coupling constants fail to correlate with substituent electronegativity.
Application of NMR spectroscopy of chiral association complexes. 8—Rotation about the C(sp2)–C(aryl) Bond in 2,6–disubstituted benzamides
Authors: Holik Miroslav , Mannschreck Albrecht 
Published: May 2005

AbstractThe barrier to rotation about the C(sp2)C(aryl) single bond in non‐planar benzoyl compounds was investigated using N,N‐dimethyl, N,N‐tetramethylene and N,N‐diisopropyl derivatives of 2,4,6‐trimethylbenzamide and 2,6‐dimethoxybenzamide and N,N‐dimethyl derivatives of the corresponding thiobenzamides. Their 1H and 13C NMR spectra were determined and assigned and the splittings in the 1H spectra due to the addition of the optically active shift reagent (+)‐Eu(hfbc)3, are discussed. The free enthalpy of activation was calculated from the coalescence temperature of the ortho‐methyl or ‐methoxyl signals and from a line‐shape analysis. An exact equation for the determination of the rate constant at coalescence and a valid approximation which includes the line‐width are presented. A distinct effect of the size of the N‐substituent on the barrier to rotation in 2,6‐dimethoxybenzamides was observed, while the π values for the 2,4,6‐trimethylbenzamides studied are practically identical.
Nitrogen‐15 nuclear magnetic resonance spectra of isocyanates, isothiocyanates and N‐sulfinylamines
Authors: Yavari Issa , Staral John S. , Roberts John D. 
Published: May 2005

AbstractThe 15N NMR spectra of ten isocyanates, four isothiocyanates, and four N‐sulfinylamines have been obtained at the natural‐abundance level by high‐resolution NMR spectroscopy. The results show that isocyanates and isothiocyanates have 15N chemical shifts over 200 ppm toward higher fields compared to those of N‐sulfinylamines. The sensitivity of the 15N shifts in these substances to substituent and electronic effects are discussed.
13C NMR spectra of 8‐aryl‐8‐azabicyclo[3.2.1]oct‐3‐en‐2‐ones and related compounds
Authors: Katritzky Alan R. , Dennis Nicholas , Sabongi Gebran J. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of various 8‐aryl‐8‐azabicyclo[3.2.1]oct‐3‐en‐2‐ones and other related compounds, including tropinone, were determined, and the predominant conformation at the bridgehead nitrogen was established. The full assignment of resonances from proton decoupled and coupled spectra was based on the analysis of the splitting pattern and characteristic chemical shifts. The use of the determined 13C NMR spectra in the assignment of 13C NMR data in related but more complicated structures is also proposed.
The 13C NMR titration shifts of sulphonic acids
Authors: Kosugi Yoshio , Takeuchi Tsugio 
Published: May 2005

AbstractCarbon‐13 chemical shifts of a number of alkyl and aromatic sulphonic acids in sulphuric acids in sulphuric acid and strongly basic deuterium oxide have been compared. The titration shifts are relatively small for carbons near the sulphonyl group, but are comparable with those of other organic acids or bases for carbons remote from the deprotonation sites.
1H NMR studies on intramolecular hydrogen bonding in perchlorates of N‐(pyridyl)amides of 6‐methylpicolinic acid N‐oxide
Authors: Brzezinski Bogumil 
Published: May 2005

AbstractThe 1H NMR spectra of perchlorates of N‐(pyridyl)amides of 6‐methylpicolinic acid N‐oxide (PYAP) in CD3CN at 100 MHz show two proton signals belonging to two distinct intramolecular hydrogen bonds. The position of these signals is independent of concentration and temperature. That of the proton of the NH ⃛O bond in PYAP is shifted to still lower field than in N‐(pyridyl)amides of 6‐methylpicolinic acid N‐oxide (PYA) due to the inductive effect of the pyridine cation and the formation of another intramolecular hydrogen N+H ⃛O bond. The proton of the N+H ⃛O bond interacts strongly with its environment and is highly sensitive to traces of water. Presumably, water leads to dissociation of the intramolecular bond.
Signs of heteronuclear spin–spin coupling constants in 15N‐acetamide
Authors: De Marco Antonio , Llinás Miguel 
Published: May 2005

AbstractBy using digital deconvolution to improve spectral resolution, earlier NMR studies on 15N‐enriched acetamide have been revised and extended to determine the signs of the heteronuclear spin‐spin coupling constants. 1J(13CO15N), 2J(13CH315N) and 3J(C1H315N) are negative while 3J(1H13CH3)>0. The results, interpreted on the basis of the ‘selective decoupling’ formalism, were confirmed by computer simulation of the double resonance spectra. It is shown that 2J(1H‐α13CO) is significantly larger than 2J(1HN 13CO). Thus, jointly with {1H‐β}‐13C′ double resonance experiments, {1H‐α}‐13C′ experiments ought to be most helpful when assigning peptide group carbonyl resonances. The study provides valuable information for the interpretation of heteronuclear coupling constants in polypeptides.
Über die Anwendung von Lanthaniden‐Verschiebungs‐Reagenzien (LSR) bei der Strukturbestimmung flexibler Moleküle, am Beispiel des 2‐Methyltetrahydropyrans und des cis‐4‐Methyl‐2‐(2′‐methyl‐1′‐propenyl)‐ tetrahydropyrans
Authors: Ribó Josep M. , Serra Xavier 
Published: May 2005

AbstractDas Modell von Davis und Willcott lässt sich erfolgreich auf die LIS‐Werte von 2‐Methyltetrahydropyran mit Eu(dpm)3 anwenden. Im Fall des cis‐4‐Methyl‐2‐(2′‐methyl‐1′‐propenyl)tetrahydropyrans (cis‐Rosenoxyd) hingegen versagt es, wahrscheinlich weil in Lösung mehr als ein Komplex LSR‐Substrat vorliegt.
Structural assignments in isomeric pyrazoles based on 3J(15NH) coupling constants
Authors: Axenrod T. , Watnick C. M. , Wieder M. J. 
Published: May 2005

AbstractVicinal 15N–H coupling constants are used to characterize the isomeric pyrazoles obtained from the condensation of phenylhydrazine, 15N‐enriched at the amino nitrogen atom, with various 1,3‐diketones.
ESR‐Untersuchungen zur Struktur der 1,2‐Thiazet‐yle, einer Neuen Klasse Stabiler Radikale
Authors: Mayer Roland , Bleisch Siegfried , Domschke Günter , Tkáč Alexander , Staško Andrej , Bartl Anton 
Published: May 2005

AbstractDie Strukturen von Benzo[c]‐ und Naphtho[2,1‐c]‐thiazet‐yl wurden durch ESR‐Spektroskopie (einschließlich Simulation der Spektren und Untersuchung entsprechender 15N‐ und N‐D‐Verbindungen) und durch massenspektroskopische Studien bestimmt. Diese neue Klasse stabiler Radikale, die aus unterschiedlichen Ausgangsverbindungen zugänglich ist, gehört zu einem sauerstofffreien Typ von N‐Radikalen.
Assignment of indirect 13C, 1H couplings in the 13C NMR spectra of some purine and pyrimidine nucleosides and their analogues by long‐range selective 1H decoupling
Authors: Uzawa Jun , Uramoto Masakazu 
Published: May 2005

AbstractThe assignments of the long‐range 13C, 1H coupling constants in the 13C NMR spectra of the base moieties of several purine and pyrimidine nucleosides and their analogues were established by the application of long‐range selective 1H decoupling with low‐power 1H irradiation. The 3J values between the carbons and protons of the pyrimidine ring in these compounds were larger than the 2J values. The conformational preference of these nucleosides in solution was shown to be predominantly anti from the value of the vicinal 13C, 1H coupling constants between H‐1′ and the base carbons through the glycosidic bond.
1H‐ und 13C‐NMR‐spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3‐Dioxan‐2‐ylium‐Salzen
Authors: Paulsen Hans , Schüttpelz Eike 
Published: May 2005

AbstractVon einer Serie an C‐2 sowie an C‐4, C‐5 und C‐6 substituierten 1,3‐Dioxan‐2‐ylium‐Salzen wurden 1H‐und 13C‐NMR‐Spektren vermessen. Nach der MINDO/3‐Methode wurde die Ladungsverteilung in 1,3‐Dioxan‐ und 1,3‐Dioxolan‐2‐ylium‐Kationen berechnet. Eine lineare Beziehung besteht zwischen π‐Ladungen und 13C‐chemischen Verschiebungen von C‐2. Die starke Tieffeldverschiebung an Protonen am C‐21 wird auf Anisotropie‐Einflüsse des mesomeren kationischen Systems zurückgeführt. Die Konformationen der substituierten 1,3‐Dioxan‐2‐ylium‐Kationen werden diskutiert.
A correlation of substituent effects with proton chemical shifts in aromatic tetrazolic acids
Authors: Ciarkowski Jerzy , Kaczmarek Józef , Grzonka Zbigniew 
Published: May 2005

AbstractThe effect of substituents on the proton chemical shifts and spin–spin coupling constants in ortho‐, meta‐ and para‐substituted 5‐phenyltetrazoles (tetrazolic acids) in DMSO–CH3CN (1:1, v/v) was studied. With the meta‐ and para‐ substituted compounds the additivity rule of chemical shifts was obeyed, thereby enabling increments characterizing the effects of individual substituents in monosubstituted benzenes to be determined. By employing the Smith and Proulx equation, the chemical shifts of the aromatic protons were correlated with the F, R and Q substituent constants. The values of these constants are 1.02, −0.004 and 5.49, respectively, for the tetrazolyl substituent.
13C‐NMR‐spektroskopische und stereochemische Untersuchungen. XXIII.—Konformationen, 13C‐NMR‐Verschiebungen‐ und 13C1H‐ Kopplungen bei Pinanverbindungen
Authors: Weigand Eckehard F. , Schneider Hans‐Jörg 
Published: May 2005

AbstractDie 13C‐NMR‐Verschiebungen bei Bicyclo[3.1.1]heptylverbindungen werden auf Grund von weitgehend molekülmechanisch errechneten Geometrien diskutiert. Dabei ergeben sich für den Grundkörper zwar energetische Minima bei Sesselformen, deren übergang jedoch so schnell erscheint [Δ*∼0,6 kcal (2.51 kJ) bei voll relaxierten Zuständen], daß für den Grundzustand von flachen Y‐Konformationen auszugehen ist. In Pinanderivaten mit equatorialen Substituenten werden Sesselformen erhalten, welche bei Einführung axialer Substitutenten stark abgeflacht erscheinen. Dadurch treten konformativ vermittelte Substituenteneffetke auf die 13C‐Verschiebungen auf, welche z.B. + 7,45 ppm Entschirmung durch eine γ‐Methylgruppe betragen können. Die teils aus 1H‐teilentkoppelten 13C‐Spektren gewonnenen 1J(CH)‐Werte werden mit berechneten Hybridisierungen der CH‐Bindungen verglichen; ihr bis zu 145 Hz (\documentclass{article}\pagestyle{empty}\begin{document}$ \buildrel \wedge \over = $\end{document}29%) reichender Wert im Cyclobutanteil der Pinane ist auch für die 13C‐Signalzuordnung von Nutzen. Eine Reihe von Literatur‐Verschiebungszuordnungen muß u.a. auf Grund von Messungen spezifisch deuterierter Verbindungen revidiert werden.
Comparative 13C NMR study of deuteriated and undeuteriated dibenzothiophenes, dibenzofurans, carbazoles, fluorenes and fluorenones
Authors: Giraud Jean , Marzin Claude 
Published: May 2005

AbstractThe NMR assignments of all carbons of dibenzothiophene and its S‐oxides, dibenzofuran, various carbazoles, fluorene and fluorenone have been carried out using deuteriated derivatives and lanthanide shift reagents. Chemical shifts and coupling constants are discussed as a function of the nature of the central ring.
Geminal C,H spin coupling in substituted alkenes
Authors: Vögeli U. , Herz D. , Philipsborn W. Von 
Published: May 2005

AbstractTwo‐bond C,H coupling constants for the coupling pathways C_CH_ (type I) and (type II) have been studied in a variety of mono‐, di‐ and trisubstituted ethylenes. For 2J(CH) of type I, additive increments have been determined for 20 substituents, which allow a satisfactory calculation of coupling constants, including relative signs, in di‒ and trisubstituted ethylenes. Several applications for E/Z isomers are presented. In cyclic compounds a positive coupling increment, δJ, is observed in going from 6‒ to 5‒membered ring compounds.
An NMR study of 2‐alkoxy‐1,3,2‐dioxaphospholanes. I—13C chemical shifts
Authors: Besserre D. , Coffi‐Nketsia S. 
Published: May 2005

AbstractMeasurements of the 13C chemical shifts of 2‐alkoxy‐1,3,2‐dioxaphospholanes have allowed the determination of the contribution of the substituent to the α‐, β‐ and γ‐carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constants J(31P13C) and the existence of linear correlations between the shifts of carbon atoms in the P‐alkoxy groups and the degree of substitution of the observed carbon or of its neighbours.
Nitrogen NMR sudies of some 15N labelled sydnones and related stuctures
Authors: Stefaniak L. , Witanowski M. , Kamieński B. , Webb G. A. 
Published: May 2005

Abstract15N NMR studies on some signly labelled sydnones, N‐acetylsydonimines and their hydrochlorides, as well as those on some sydnonimine hydrochlorides, show that in each case protonation takes place at the exocyclic moiety, \documentclass{article}\pagestyle{empty}\begin{document}$ - {\rm O}^ \ominus - \mathop {\rm N}\limits^ \ominus {\rm COCH}_3 \,{\rm or}\, - \mathop {{\rm NH}}\limits^ \ominus $\end{document}, respectively. Complete assignments of the nitrogen chemical shifts are possible for the labelled compounds, including the isomeric structures of N‐alkyl–N‐cyanomethyl–N–nitrosoamines to which, unstable, free sydnonimines are converted.
Polyhaloheterocyclic compounds. Part XXXI—carbon‐13 NMR spectra as a structural probe for polychloroaromatic compounds
Authors: Chambers Richard D. , Matthews Raymond S. , Kenneth W. , Musgrave R. , Urben Peter G. 
Published: May 2005

AbstractCarbon‐13 spectra of twelve chlorofluoropyridines (C5CInF5−nN), of known structure, have been assigned and an assessment has been made of the degree of additivity of substituent chemical shifts (SCS). Reasonable additivity is observed for pyridine derivatives but little regulatiry can be inferred from the spectra of perchlorinated‐diazines and ‐triazines. There is an approximately linear relationship between 13C and 19F chemical shifts.
Application of 15N spectroscopy and dynamic NMR to the study of ureas, thioureas and their lewis acid adducts
Authors: Martin M. L. , Filleux‐Blanchard M. L. , Martin G. J. , Webb G. A. 
Published: May 2005

AbstractRotational barriers and 15N chemical shifts have been measured in a number of ureas and thioureas. As anticipated on the basis of the 15N shifts, several previously unobserved rotational barriers could be detected by using lanthanide reagents or a high field spectrometer. Nearly constant effects on both the rotational activation energy and the 15N shift are produced on going from ureas to the corresponding thioureas, and correlations are found between the ΔG‡ and δ15N values. The results are discussed in terms of lone pair delocalization, and anomalies with respect to the general behaviour are tentatively explained in the light of the effect of steric torsion in crowded structures on the 15N shifts and rotation barriers.
13C nuclear magnetic resonance of organophosphorus compounds XI—aminophosphines
Authors: Gray George A. , Nelson John H. 
Published: May 2005

AbstractNatural abundance 13C NMR studies have been carried out on a series of organophosphorus compounds possessing PN bonds. For the first time a one‐bond temperature‐dependent 13C—31P nuclear spin coupling was observed for the P‐phenyl carbons in bis(N,N‐dibenzylamino)phenylphosphine (0‐9 Hz) and bis(N,N‐diethylamino)phenylphosphine (0–2 Hz). This temperature‐dependent behavior can be rationalized in terms of free rotation about the phenyl phosphorus bond with concomitant hindered rotation about the PN bonds. A conformational preference for the nitrogen and phosphorus lone pairs to exist in the trans orientation is indicated. In the similarly substituted 5‐membered heterocyclic ring compound, 1,3‐dimethyl‐2‐phenyl‐1,3‐diazaphospholidine, the phenyl one‐bond coupling increases to (−) 42.1 Hz and becomes temperature independent. These data suggest that 1J(PC) is very responsive to electronic effects.
Carbon‐13 NMR studies of nitrogen compounds. I—substituent effects of amino, acetamido, diacetamido, ammonium and trimethylammonium groups
Authors: Llinarés Jeanine , Elguero José , Faure Robert , Vincent Emile‐Jean 
Published: May 2005

Abstract13C NMR chemical shifts are reported for several alkyl or aryl amines, acetamides, diacetamides and ammonium and trimethylammonium salts. Substituent effects, determined with respect to chemical shifts of amino derivatives, are rationalized in terms of γ effects, steric interactions and for benzene derivatives, in terms of competition between inductive (σ1) and resonance (σR) effects. These perturbations can be used to assign chemical shifts of complex structures and to study certain chemical processes.
Investigation of substituent effects on the 1H and 13C NMR spectra of ferrocene analogues of chalcones
Authors: Solčániová E. , Toma S. , Fiedlerová A. 
Published: May 2005

AbstractThe transmission of electronic effects across the ferrocene analogues of chalcones [3‐aryl‐1‐ferrocenyl‐2‐propene‐1‐ones (series 1) and 1‐aryl‐3‐ferrocenyl‐2‐propene‐1‐ones (series 2)], as well as the conformations of both types of ferrocene analogues have been studied. The ferrocene analogues of chalcones of series 1 were found to be in a non‐planar conformation. Their H‐α and C‐α chemical shifts are more sensitive to the resonance than to the inductive effects of substituents. The C‐α chemical shifts of the ferrocene analogues of chalcones of series 2 are more sensitive to the inductive than to the resonance effects of substituents. The transmission of the substituent effects to the ferrocene moiety is also briefly discussed.
Detection of halogen bond formation by correlation of proton solvent shifts. II—methylene halides in n‐electron donor solvents
Authors: Bertrán José Fernández , Rodríguez Mario 
Published: May 2005

AbstractThe solvent shifts of the methylenic protond of CH2Cl2, CH2Br2 and CH2I2 have been measured in amines, ethers and non‐polar solvents. Correlation of the solvent shifts of the bromine and iodine compounds ΔCl, serves as a monitor of halogen bonding interactions which are competitive with hydrogen bonding association. Amines interact with CH2I2 via a halogen bond while in ethers hydrogen bonding predpminates. CH2Br2 shows solute–solvent interactions identical to CH2Cl2.
Localization of N‐oxide groups by means of nitrogen chemical shifts
Authors: Witanowski M. , Stefaniak L. , Kamieński B. , Webb G. A. 
Published: May 2005

AbstractThe applicability of nitrogen chemical shifts to the localization of N‐oxide groups in azine ring systems is exemplified by 1,2,4‐triazine systems. The average excitation energy approximation in the theory of magnetic shielding gives a good linear correlation with the nitrogen shieldings in azine N‐oxides.
A CNDO/2 study on the additivity and the nature of the non‐additivity of the substituent effects on 13C NMR shifts in chlorobenzenes and chlorophenols
Authors: Laatikainen Reino 
Published: May 2005

AbstractThe general correlation between the electron densities and the 13C NMR chemical shifts is found to be quite poor in the cases discussed. The non‐additivities of the substituent effects on the chemical shifts and the CNDO/2 electron densities correlate only weakly. However, when the electron densities are made specific to different types of atomic orbitals, the s electrons have a pronounced effect in all the models tested. This is explained by an indirect effect on the 〈1/r3〉 term of the p electrons. Good correlations are found between the sums of the chemical shifts and the corresponding sums of the substituent charge excesses. The different behaviour of OH and Cl substituents in the additivity of the substituent effects can be explained by their different back‐bonding properties.
Reversed substituent effect for the 13C NMR chemical shifts in the unsubstituted ring of para‐substituted benzophenones
Authors: Frahm August W. , Hambloch Heinrich F. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of the C‐1′ carbon atom of fifteen para‐substituted benzophenones correlate with the ℱ and ℛ substituent constants in a reversed manner.