bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Carbon‐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

Carbon‐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

The 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

By 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

Das 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

Vicinal 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

Die 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

The 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

Von 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

The 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

Die 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

The 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

Two‐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

Measurements 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

15N 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

Carbon‐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

Rotational 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

Natural 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

13C 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

The 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

The 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

The 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

The 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

The 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.
Evidence for strong intramolecular hydrogen bonding in some quinoline derivatives
Authors: Ballbio Marzia , Nero Stefano Del , Vigevani Aristide
Published: May 2005

Several analogues of quinoline‐8‐carboxamide were examined by 1H NMR and IR in order to establish structural requirements for strong intramolecular hydrogen bonding.
1H and 31P NMR spectra of the phenyl ester of dichlorophosphoric acid in a nematic phase
Authors: Hansen J. , Jacobsen J. P.
Published: May 2005

The 1H and 31P NMR spectra of the phenyl ester of dichlorophosphoric acid dissolved in Merck nematic phase IV have been recorded and analysed. The values of the dipole dipole couplings have been discussed in terms of several different geometric models. Non‐planarity of C‐1, O, P and the phenyl ring must be assumed in order to account for the results; a twist angle of 49° was found.
The relationship between proton–proton NMR coupling constants and substituent electronegativities. II—conformational analysis of the sugar ring in nucleosides and nucleotides in solution using a generalized Karplus equation
Authors: Haasnoot C. A. G. , de Leeuw F. A. A. M. , de Leeuw H. P. M. , Altona C.
Published: May 2005

The relationship between vicinal NMR proton–proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on 3J(HH); second, empirical correlations between the parameters governing the conformation of β‐D‐furanosides (taken from an analysis of 178 crystal structures) were used to define proton–proton torsion angles as a function of the pseudorotation parameters P and Φm; and, third an iterative least‐squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′‐cyclic nucleotides, a base‐stacked ribonucleotide, 2′‐anhydroarabinonucleosides, α‐D‐2′,2‐O‐cyclouridine, 2′‐ and 3′‐aminosubstituted ribonucleosides, 2′‐ and 3′‐deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.
1H and 13C nuclear magnetic resonance study of (D3)‐trishomocuban‐4‐ol and (D3)‐trishomocubanone
Authors: Dekker Theodor G. , Oliver Douglas W. , Pachler Klaus G. R. , Wessels Philippus L. , Woudenberg Marianne
Published: May 2005

The complete assignments of the 1H and 13C NMR spectra for (D3)‐trishomocuban‐4‐ol (3) and (D3)‐trishomocubanone (4) are reported. The difference between the 1H and 13C chemical shifts of 3 and 4 and those of the hydrocarbon (D3)‐trishomocubane, and the substituent effect of the hydroxy group, can be adequately explained by the unique stereochemistry of these compounds.
Prediction of ortho(β) 13C chemical shifts in conjugated systems
Authors: Craik D. J. , Ternai B.
Published: May 2005

An equation has been developed which relates ortho or C‐β 13C substituent chemical shifts (SCS) to the ortho proton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho 1H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho 13C data in 2‐naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.
Effect of lanthanide shift reagents on conformational equilibria
Authors: Dixon J. R. , McIntyre P. S. , Morris I. G. , Williams D. L.
Published: May 2005

The conformational equilibrium constants for a series of 1‐alkyl substituted cyclohexanols have been determined using a lanthanide shift reagent, and the results compared with other methods. In comparison to other technique greater preference is shown by the hydroxyl group for the equatorial position. This is rationalized by the effect on the equilibrium of the bulky shift reagent.
Correlation of nitrogen‐14 nuclear quadrupole resonance data in sulfanilamides with the in vitro activities
Authors: Subbarao S. N. , Bray P. J.
Published: May 2005

Several sulfanilamide‐type compounds in their solid state have been investigated by the 14N nuclear quadrupole resonance (NQR) technique. The electron distributions at the sites of the nitrogen atoms, calculated by the Townes and Dailey theory, indicate a significant correlation between the quadrupole coupling constant for the primary amino nitrogen (N4), which is a measure of the (π‐σ) electron density at N4, and the in vitro bacteriostatic activity of the sulfanilamides.
The 1H and 13C chemical shifts for some tetrakis(para‐substituted phenyl)ethylenes
Authors: Smith William B.
Published: May 2005

The proton and carbon chemical shifts for a series of tetrakis(p‐substituted phenyl)ethylenes are described. Assignments followed routine substituent chemical shift trends. Both proton and carbon chemical shifts ortho to the varying substituent follow the empirical parameter, Q. The ethylene carbon chemical shifts are proportional to those at the position para to the varying substituent.
The configuration and conformation of the tricyclo[4.4.1.12,5]dodecan‐11‐ols determined by 1H NMR spectroscopy using the shift reagent Eu(fod)3
Authors: Mason Timothy J.
Published: May 2005

The isomeric tricyclo[4.4.1.12,5]dodecan‐11‐ols have been synthesized from the (6+4) cycloaddition product of tropone with cyclopentadiene. The configuration and conformation of each isomer was determined from the proton shift gradients induced in the olefinic proton signals in the 1H NMR spectra of intermediate compounds by Eu(fod)3.
Carbon‐13 NMR characterization of the bispyridinium oximes, toxogonin, HS‐3, HS‐6 and HI‐6
Authors: Waysbort D. , Balderman D. , Amitai G.
Published: May 2005

The structure of the bispyridinium oximes, toxogonin, HS‐3, HS‐6 and HI‐6, used as antidotes in organophosphorus poisoning, is confirmed by 13C NMR spectroscopy. The 13C NMR spectra of the corresponding monopyridinium precursors substantiate the signal assignment in the bispyridinium oxime spectra. In all oximes studied the hydroxyiminomethyl group (CHNOH) exists in the syn configuration. The 13C signal differences also readily allow analysis of binary mixtures of the oximes and provide an easy method for monitoring their stability.
Anionic lanthanide shift reagents. Application to the assignment of NH peaks of amidinium ions
Authors: Perrin Charles L.
Published: May 2005

Anionic EDTA complexes of Pr(III) and Eu(III) produce downfield and upfield shifts, respectively, of the NH resonances of amidinium ions, RC(NH2)2+. These LnEDTA− ‐induced shifts arise through the formation of weak ion pairs. Results for the acetamidinium ion show that Hz, the high field NH, experiences a greater shift than HE. This result confirms the expectation that in the ion pair the anionic shift reagent approaches closer to Hz. Thus LnEDTA−‐induced shifts can be used to assign NH peaks of amidinium ions. Such shifts are then used to assign the low field NH peak of the benzamidinium ion to HE, whereas the low field NH peaks of the azoisobutyramidinium ion and formamidinesulfinic acid are assigned as Hz.
13C NMR spectroscopy of the withanolides and other highly oxygenated C28 steroids
Authors: Gottlied Hugo E. , Kirson I.
Published: May 2005

The 13C NMR spectra of 29 highly oxygenated C, steroids with the withanolide skeleton, 24 of which are naturally occurring substances or acetates thereof, were recorded and the carbon signals fully assigned. The shifts of the heavily functionalized A/B ring system can serve as a ‘fingerprint’ for the different substitution patterns. A study of the effects of hydroxyl substitution in the ring D/side chain part of the molecules leads to conformational information, including preferred rotamers around the 17—20 and 20—22 bonds. Systems with both 17α‐ and 17β‐oriented side chains are thus analysed.
Configuration and 13C NMR spectra of 1‐pyrazolines
Authors: Touillaux R. , Tinant B. , Van Meerssche M. , Dereppe J. M. , Leroy G. , Weiler J.
Published: May 2005

A comparative study of the 13C spectra of 13 1‐pyrazolines is reported. The results show that the chemical shifts of some carbons are very sensitive to the relative positions of substituents on the 3,4 and 4,5 bonds.
13C NMR spectroscopy of cyclopropane derivatives. 1—monocyclic compounds
Authors: Rol N. C. , Clague A. D. H.
Published: May 2005

The 13C NMR data of an appreciable number of cyclopropane derivatives have been collected. Most of the spectra were recorded by ourselvesand some were taken from the Literature. With a view to furthering the useof 13C NMR spectroscopy as a diagnostic tool in this field, we havemeasured not only the chemical shifts,δ, but also the coupling constants 1J(CH). It is shown that both embody valuable structural information.
Additive NMR chemical shift parameters for deshielded methine protons
Authors: Bell Harold M. , Bowles Deborah B. , Senese Fred
Published: May 2005

The use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron‐withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm.
Vicinal C,H spin coupling constants in determining alkene stereochemistry
Authors: Letcher R. M. , Acheson R. M.
Published: May 2005

Further examples of the diagnostic vicinal C,H coupling constants of trisubstituted alkenes are reported, and the application of the method confirms the structures of four dimethyl acetylenedicarboxylate adducts.
An experimental study of some NMR methods for the measurement of slow exchange rates
Authors: Baine P. , Gerig J. T. , Stock A. D.
Published: May 2005

The rates of interconversion of the cis and trans rotational isomers of N‐trifluoroacetyl‐N‐methylbenzylamine have been determined by a variety of NMR lineshape experiments and by several double resonance methods. Comparison of the results for the slow exchange region suggests that a Fourier transform version of the transfer of saturation method of Forsen and Hoffman, as well as transfer of magnetization after selective 180° inversion of the resonance of one rotamer, give rate constants nearly as reliable as lineshape methods. Use of the rate of signal recovery after saturation of the resonance of one rotamer gave results which were less accurate. The available data produced the following activation parameters for amide rotation in this compound: ΔG‡, 18.9 kcal mol−1; ΔH‡, 22.3 kcal mol−1 and ΔS‡, 9.8 e.u. when the solute was 2 M in 1,1,2,2‐tetrachloroethane‐d2.
1H NMR and 13C NMR spectra of disulfides, thiosulfinates and thiosulfonates
Authors: Freeman Fillmore , Angeletakis Christos N. , Maricich Tom J.
Published: May 2005

The 1H NMR and 13C NMR spectra of neopentyl and benzyl substituted disulfides, thiosulfinates, thiosulfonates, thiols, sulfides, sulfinic acids and sulfonic acids are reported. The deshielding electron withdrawing effects of −SO, −SO2, −SO2−, −SO2H, −SO3−, −SO3H and SO3CH3 on α‐methylene and benzylic protons are observed. The 1H NMR spectra show, except for two dialkylthiosulfinates, that the α'‐protons of thiosulfinates absorb farther downfield than those of the thiosulfonates. Although the 13C NMR spectra show that αSO effects are deshielding and are smaller than the αSO2 effects, the α'SO values are more shielding than the α'SO2 values for some compounds. The effects on 13C NMR spectra which result from substituting a phenyl group for a neopentyl or benzyl group are discussed. The α‐methylene carbon shifts for neopentanesulfinic acid and α‐toluenesulfinic acid are further downfield than those for the corresponding sulfonic acids.
Carbon‐carbon coupling in [3‐13C1]tryptophan
Authors: London R. E.
Published: May 2005

Carbon‐carbon coupling constants have been observed in [90% 3‐13C1]tryptophan and used to assign the 13C resonances of the indole ring. The results support a reassignment of C‐5 and C‐6 recently suggested on the basis of the reassigment of the corresponding resonances in indole. Coupling constants are compared with theoretical values obtained using a finite perturbation theory Blizzard‐Santry program, and excellent agreement is obtained for the 1J(CC) values. The calculations predict that the Fermi contact contribution is dominant for all nJ(CC) couplings to C‐3.
Carbon‐13 NMR spectra of some epoxides derived from dicyclopentadiene
Authors: Matoba Yasuhiro , Kagayama Takashi , Ishii Yasutaka , Ogawa Masaya
Published: May 2005

The 13C NMR spectra of a series of epoxides derived from endo‐ and exo‐dicyclopentadiene and their partially hydrogenated compounds were determined to examine the substituent effects arising from the introduction of the oxirane ring in comparison with those found in other ring systems. The 13C signals of some epoxides were assigned by using lanthanide shift reagents. Characteristic substituent effects exerted by an oxirane ring were demonstrated. Marked steric γ‐effects of −8—13 ppm were observed at the bridge carbon signal in the bicyclo[2.2.1]heptane skeleton. Differences were found in the substituent effects between endo‐ and exo‐dicyclopentadiene epoxides, and have been discussed in relation to the molecular geometry.
Substituent effects on carbon‐13 chemical shifts in 2,6‐disubstituted adamantanes
Authors: Majerski Zdenko , Vinković Vladimir , Meić Zlatko
Published: May 2005

Carbon‐13 NMR spectral data for a series of symmetrical 2,6‐disubstituted adamantanes (O, CH2, CH3, OH, OCOCH3) are presented. The substituent effects on 13C chemical shifts are additive, except for carbons 2 and 6 in 2,6‐adamantanedione. The non‐additivity of the substituent effect in the diketone can be interpreted in terms of a through‐space interaction of the carbonyl π‐electrons; the additivity in the other derivatives indicates that there is no appreciable interaction between the substituents.
Transmission mechanisms of inter‐proton long‐range couplings in substituted anisoles
Authors: de Kowalewski D. G. , Contreras R. H. , Engelmann A. R. , Facelli J. C. , Durán J. C.
Published: May 2005

Inter‐proton long‐range and ring couplings were measured in o‐anisaldehyde and in seven disubstituted anisoles. In order to investigate the transmission mechanisms of long‐range couplings with the methoxy group, partially restricted molecular orbital (PRMO) calculations were carried out within the FPT‐INDO method on o‐anisaldehyde. σ‐ and π‐electron, and through‐space transmitted components were separated. For the energetically favoured trans‐OMe conformation a through‐space component was found for the couplings of the methyl protons with the ortho‐proton, and it was found that its sign, as well as its magnitude, depends on their relative positions. If free rotation, however, is assumed for the methyl group, the averaged value for this coupling constant is negative.
Carbon‐13 NMR signals of some natural coumarins and their derivatives
Authors: Patra Amarendra , Mitra Alok K.
Published: May 2005

The 13C NMR spectra of the natural coumarins ostruthin, osthol, aegelinol (enantiomer of decursinol), luvangetin, seselin, anomalin, oxypeucedanin (and its enantiomer prangolarin) and oxypeucedanin hydrate and some of their derivatives have been studied. Self‐consistent resonance assignments have been made following chemical shift theory and using simple models. Carbon‐hydrogen coupling constants of some compounds are also reported. The alkoxy group/s at C‐5 and/or C‐8 in linear furocoumarins, as well as in linear pyranocoumarins, have unusually small shielding effects on the ortho‐ and para‐carbons. This study also indicates that the C‐4a and C‐8 resonance assignments of osthol, made earlier, should be reversed.
Carbon‐13proton coupling constants in N‐substituted imidazoles. A 13C NMR study and MO calculations
Authors: Pachler K. G. R. , Pachter R. , Wessels P. L.
Published: May 2005

The 13C NMR data of imidazole, and N‐methyl‐, N‐acetyl‐, N‐trifluoroacetyl‐, N‐heptafluorobutyryl‐ and 2‐methyl‐imidazoles, were obtained from proton‐noise decoupled and single frequency NOE 13C NMR spectra. The considerable changes in the directly‐bonded (C, H) coupling constants upon N‐acetylation of the imidazole ring, which are comparable to those noted when going from the neutral to the cationic form of imidazole, are primarily due to the large π‐electron transfer ability of the N‐acetyl‐ and N‐trifluoroacetyl‐substituents. The differences in magnitude of the three‐bond (C, H) coupling constants along different paths in the imidazole ring may be attributed to the larger π‐contributions across a pyridine‐like nitrogen than along a pyrrole‐like nitrogen.
Deuterium‐induced 13C nuclear magnetic resonance isotope shifts and 13C2H couplings for signal assignments and determination of deuteration site in cyclooctanone
Authors: Milosavljević Slobodan , Jeremić Dragoslav , Mihailović Mihailo Lj. , Wehrli Felix W.
Published: May 2005

Unambiguous signal assignments in the 13C spectra of monodeuterated cyclooctanones derived from the lead tetraacetate or silver oxide/bromine oxidations of the corresponding 1‐monodeutero‐alcohols have been obtained from deuterium‐induced 13C isotope shifts and geminal and vicinal 13C2H spin‐spin coupling constants. The label in the ketones is shown to be in position 5.
17O NMR investigation of p,π‐interactions in α,β‐unsaturated and aromatic ethers
Authors: Kalabin G. A. , Kushnarev D. F. , Valeyev R. B. , Trofimov B. A. , Fedotov M. A.
Published: May 2005

The 17O chemical shifts have been measured for 51 α,β‐unsaturated and aromatic ethers. A good linear relationship is found between the 17O chemical shifts in a series of dialkyl and the corresponding alkyl vinyl ethers. Hence, the extent of p,π‐interaction, between the oxygen atom and the vinyl group in the latter series does not, apparently, depend upon branching at the α‐carbon atom in the alkyl moiety of these ethers. The PhOBut ether, however, as compared to the other alkyl phenyl ethers, shows significantly weakened p,π‐interaction, which is apparently related to the steric hindrance of this interaction. The effects of two unsaturated groups upon the 17O chemical shifts in the corresponding ethers are non‐additive. This is undoubtedly a result of ‘rivalry’ between these groups for conjugation with the lone electron pairs on the ethereal oxygen. The 17O chemical shift ranges of substituted methyl and vinyl phenyl ethers are nearly equal (≈30 ppm). An analysis of the 17O shielding for cyclopropyl ethers shows no observable p,σ‐conjugation in these compounds. Excellent correlation (r>0.99) between the values of 17O chemical shifts and the calculated (MO LCAO SCF, CNDO/2) π‐electron charges on the corresponding oxygen atoms look promising for experimental estimations of π‐electron densities on the ethereal oxygen.
Chemistry of 6H‐pyrido [4, 3‐b] carbazoles. Part 10—Carbon‐13 nuclear magnetic resonance spectra of ellipticines and some model compounds
Authors: Sainsbury M. , Watkins D. , Weerasinghe D. K.
Published: May 2005

The 13C NMR spectrum of ellipticine has been re‐interpreted by reference to model compounds, and correlated with the spectra of a number of new ellipticine derivatives.
Indirect negative nuclear Overhauser effects: Observation and applications
Authors: Mersh John D. , Sanders Jeremy K. M.
Published: May 2005

Direct positive and indirect negative NOEs can often be observed in the same molecule, providing a method for establishing otherwise inaccessible connectivities in complex spectra and an effective probe of conformation in solution.
The assignment of 13C NMR shift data in clerodanes and related structures
Authors: Luteijn J. M. , Van Veldhuizen A. , De Groot A.
Published: May 2005

The 13C NMR spectra of a number of partial clerodane structures and analogous compounds were recorded. The information thus obtained enabled the assignment of the 13C NMR shifts in a number of naturally occurring clerodanes.
σ‐Correlations and steric effects
Authors: Balasubrahmanyam S. N. , Mallick I. M.
Published: May 2005

Carbon‐1 shifts in 1‐dimethylimino‐3‐dimethylamino‐1‐(4‐substituted)phenylprop‐2‐ene perchlorates show high correlation and negative dependence v. a σ set having high f character, similar to α and carbonyl carbon shifts in 4‐substituted styrenes and N,N‐dimethylbezamides, respectively. In sharp contrast with the β‐carbons of the styrenes and the 15N absorptions of benzamides, whose shifts show high positive correlations with specific ratios of f and R characters, the C‐2 shifts remain invariant. In the correlation of the barriers about the N‐CO bond in N,N‐dimethylbenzamides v. f/R, the R effect has been reported to increase dramatically for the meta‐series when values determined in acetonitrile are exchanged with those determined in chloroform and, in the para series, to be higher than (normal) in both solvents. α‐Carbon shifts in tris‐para‐substituted triphenylcarbonium ions correlate with a σ set having exceptionally high R character (c. 98 %). Explanations, based mainly on the likely action of steric factors, are suggested.
Deuterium isotope effects on one‐bond carbon, hydrogen coupling constants
Authors: Everett Jeremy R.
Published: May 2005

Small, negative deuterium isotope effects on 1J(CH) have been found for a variety of simple organic molecules. These new experimental data support theoretical calculations and suggestions based on previous imprecise experimental measurements. The deuterium isotope effects upon the 13C chemical shifts were also measured with high precision.
13C NMR spectroscopy of coumarin derivatives
Authors: Duddeck Helmut , Kaiser Manfred
Published: May 2005

The 13C chemical shifts of 209 naturally occurring and synthetic coumarin derivatives are listed and a number of methods for signal assignments are explained. Substituent effects on 13C chemical shifts (SCS) in monosubstituted coumarins and non‐additivities of SCS in coumarins with more than one substituent are discussed in detail.
Oxazepines and thiazepines. XIII—conformational analysis of 2,3‐dihydrobenzothiazepine derivatives
Authors: Tóth Gábor , Szöllösy Áron , Lévai Albert , Duddeck Helmut
Published: May 2005

The conformation and relative configuration of various condensed heterocycles possessing a 2,3‐dihydro‐1,5‐benzothiazepine moiety and their synthetic intermediates were determined by 1H and 13C NMR spectroscopy. It was found that epimerization takes place during the ring closure reaction.
Conformational preference in thiophene‐2‐carbaldehyde
Authors: Salman Salman R.
Published: May 2005

The 100 MHz 1H NMR spectra of thiophene‐2‐carbaldehyde have been obtained in different solvents and analysed. It was found that the SO‐cis conformation is more stable in all solvents, and that the proportion of the SO‐trans population increases with decreasing polarity of the solvent. CNDO/2 calculations predict that the SO‐cis is more stable than the SO‐trans conformation. The aldehyde coupling to the ring was calculated by the CNDO/2 method and compared with the experimental value.
Comparative NMR study of rhamnobioses—applications
Authors: Dutton G. G. S. , Merrifield E. H. , Laffite C. , Pratviel‐Sosa F. , Wylde R.
Published: May 2005

1H and 13C NMR chemical shifts are reported for several rhamnobioses and their acetylated derivatives. The effect of substitution on the rhamnose unit has been determined with respect to the anomeric carbons and linked carbons. These effects have been rationalized and have allowed the assignment of the structure of xanthorhamnin.
The structural dependence of 13C, 13C coupling constants in cyclopropanes
Authors: Stöcker Michael
Published: May 2005

The smallest one‐bond carbon—carbon coupling constants of cyclopropane derivatives have been measured for [1‐13C]cyclopropane‐1,1‐dicarboxylic acid and cyclopropanecarboxylic acid. The 13C, 13C coupling constants of cyclopropylcarbinol have also been determined. The dependence of 1J(CC) of the three‐membered ring on different substituents and hybridization effects is evaluated. The carbon—carbon coupling constant of the unsubstituted cyclopropane is discussed on the basis of self‐consistent perturbation theory (SCPT) and s character calculations (localized bond orbitals), and the results are compared with the experimental finding. It is shown that the 1J (CC) can be interpreted by assuming a dual‐pathway coupling mechanism.
Conformations and 13C NMR shifts in tetralins
Authors: Schneider Hans‐jörg , Agrawal Pawan Kumar
Published: May 2005

Force field (MM2) calculations, 13C NMR substituent‐induced shifts (SIS) and epimeric shift differences (ESD) indicate a preference for equatorial substituents in the 2‐position, but equal eq/ax populations in the 1‐position of tetralines. Similar conclusions are reached from Yb(fod)3‐induced shifts, which are also used for signal assignments, e.g. in 1‐tetralone. Configurational assignments are possible for 1,2‐ and 1,3‐epimers (ESD up to 4 ppm) but, in line with the non‐discriminating eq/ax conformations at C‐I, not for 1,4‐epimers (ESD<0.5 ppm). More than 50 compounds were measured, including functional derivatives which show regular SIS for substituents in the aromatic moiety only for m‐ and p‐carbon atoms. OMe, but not OH or OAc substituents, induce o‐carbon SIS varying from −11 to −19 ppm. Conversion of 1‐hydroxytetralin to esters induces shielding variations at the aromatic carbon atoms which indicate the electrostatic origin of derivatization shifts.
A high‐temperature thermometer for 13C NMR spectroscopy
Authors: Field Leslie D. , Sternhell Sever , Veigel Wayne
Published: May 2005

The chemical shift difference between the carbon atoms in neat dichloroacetic acid is temperature dependent. The temperature dependence was calibrated against the melting points of pure organic compounds to provide an NMR thermometer for 13C spectroscopy.
14N NQR study of some local anesthetics
Authors: Buess M. L. , Bray P. J.
Published: May 2005

Nitrogen‐14 nuclear quadrupole resonance (NQR) spectra for eleven local anesthetics in the solid state are reported and analyzed using the Townes and Dailey approach. The changes in the electron distributions at various nitrogen sites, produced by protonating the tertiary amino nitrogen, are discussed and shown to be in general agreement with expectations based on the increased electrophilic character of the protonated amino group.
Conformational analogies of morphine agonists and antagonists as revealed by carbon‐13 NMR spectroscopy
Authors: Eliel Ernest L. , Morris‐Natschke Susan , Kolb Vera M.
Published: May 2005

The extreme similarity (except in the vicinity of the nitrogen atom) of the 13C spectra of the agonist‐antagonist pairs oxymorphone‐naloxone and morphine‐nalorphine and their respective hydrochlorides suggests that the N‐methyl and N‐allyl compounds have analogous conformations. This makes unlikely an interpretation of the agonist‐antagonist dichotomy in terms of confonnational differences. Both morphine hydrochloride and nalorphine hydrochloride exist as mixtures of two diastereomers: ca 83% of the isomer with equatorial N‐alkyl and 17% of the isomer with axial N‐alkyl (ΔG°=O.95 kcalmol−1).
13C, 77Se and 125Te NMR in ortho‐halogenated seleno‐ and telluro‐phenetoles
Authors: Baiwir Marcel , Llabrès Gabriel , Luxen André , Christiaens Léon , Piette Jean‐Louis
Published: May 2005

77Se and 125Te chemical shifts have been measured for o‐halogenated seleno‐ and telluro‐phenetoles. Correlations exist between these parameters and the halogen electronegativities or the 13C chemical shifts, except for the fluorine derivatives. The chalcogen shifts are related to the shifts of various nuclei in halobenzene derivatives, namely 1H in benzenes, 13C in toluenes, 15N in anilines and 19F in fluorobenzenes. 77Se and 125Te chemical shifts are correlated in the o‐halogenated seleno‐ and telluro‐phenetoles and in chalcogen analogues of o‐methoxy‐selenoanisole and ‐tellurophenetole: Δδ(Te) = 1.60Δδ(Se). The observed gradient is close to values previously reported for other selenides and tellurides, but differs from the value observed in heterocycles. This observation is discussed.
Substituent effects on nuclear spin–spin carbon–carbon coupling constants in derivatives of acetylene
Authors: Kamienska‐Trela K. , Biedrzycka Z. , Machinek R. , Knieriem B. , Lüttke W.
Published: May 2005

1J(13C13C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance 13C NMR spectra and in one case (triethylsilyllithiumacetylene) from the 13C NMR spectrum of a 13C‐enriched sample. It has been found that the magnitude of J(CC) depends on the electronegativity of the substituents at the triple bond. The equation 1J(13C13C) = 43.38 Ex + 17.33 has been derived for one particular series of the compounds Alk3SiCCX, where X denotes Li, R3Sn, R3Si, R3C, I, Br or Cl. The 1J(CC) values found in this work cover a range from 56.8 Hz (in Et3SiCLi) to 216.0 Hz (in PhCCCI). However, the 1J(CC) vs Ex equation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li2C2 (32 Hz) and in F2C2 (356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for 1J(CC) across a triple bond. The unusually large changes of the 1J(CC) values are explained in terms of substituent effects followed by a re‐hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn from the experimental data.