bluuebunny/crossref_metadata_2025 huggingface dataset:
Substituent chemical shifts of the organotin moiety in compounds of the type RSnMenCl3 − n (n = 0 to 3; R = n‐alkyl)
Authors: Mitchell Terence N.
Published: May 2005

The 13C and 119Sn NMR spectra of 33 organotin compounds of the type RSnMenCl3 − n and related types are discussed. The substituent effects of the groups SnMe3, SnMe2Cl, SnMeCl2 and SnCl3 (and of some related groups) on the carbon chemical shifts in the alkyl group R have been determined; the SnMe3 group causes a small upfield shift of the carbon attached to it, while the other groups cause downfield shifts. The shifts show a monotonic change on replacing methyl groups in Me3Sn by chlorine atoms. The effects on carbons further removed from the tin atom are discussed. Variation in R causes little change in nJ(SnC) or δ(119Sn).
A NMR identification of isomeric Meisenheimer adducts from 4‐nitrobenzofurazan and 4‐nitrobenzofuroxan
Authors: Terrier François , Millot François , Chatrousse Alain‐Pierre , Pouet Marie‐José , Simonnin Marie‐Paule
Published: May 2005

It has been shown by NMR spectroscopy that both 4‐nitrobenzofurazan and 4‐nitrobenzofuroxan give isomeric σ‐adducts, which result from methoxide addition at the non‐substituted 5‐and 7‐carbons.
The assignment of the 1H NMR signals to the methine bridge H‐atoms in chlorophyll derivatives
Authors: Trowitzsch Wolfram
Published: May 2005

Experiments are described which prove the assignments of the α‐ and β‐protons in the 1H NMR spectra of methyl phaeophorbide a (1) and methyl pyrophaeophorbide a (2). Because of the structural relationship between derivatives of the bacteriochlorophylls d (5) and 2, dehydration of 5 results in a homologue mixture [2‐(des‐α‐hydroxyethyl)‐2‐vinyl‐bacteriomethyl phaeophorbide] d (6) of 2. Since the homologue substituents in 6 are located at C‐4 and C‐5 surrounding the β‐H position, and since only one broad signal appears in its 1H NMR spectrum, this is assigned to the β‐proton. This experiment proves that the sequence of increasing shielding is β, α and δ in 6; and, therefore, the same sequence applies to the 1H NMR spectra of 1 and 2. This knowledge reveals that the product of electrochemical reduction of 1 in deuteromethanol is exclusively an α‐chlorin‐phlorin (8). In addition, the 1H NMR spectrum of the 2‐vinyl derivatives of the bacteriomethyl phaeophorbides c (7) shows the same broad signal at lowest field as does that of 6. The sequence of increasing shielding is therefore, β, α. The influence of the additional δ‐methyl group in 7 on the ring current is explained.
Etude RMN 13C d'aziridines non substituées sur l'azote II—Aza‐7 bicyclo[4.1.0]heptanes, configurations relatives et conformations privilégiées
Authors: Mison P. , Chaabouni R. , Diab Y. , Laurent A. , Martino R. , Lopez A. , Wehrli F. W. , Wirthlin T.
Published: May 2005

L'étude des spectres RMN 13C de dialkyl‐1,2 (ou alkylphényl) aza‐7 bicyclo[4.1.0]heptane diastéréoisomères nous a permis de déterminer leur configuration et leurs conformations priviligiées. Dans les isomères de configuration cis le substituant en position 2 est ‘pseudoaxial’ alors qu'il est ‘pseudo‐équatorial’ pour ceux de configuration trans.
Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t‐butyle (cyclohexanones disubstituées 3, 4)
Authors: Lafrance Ronald , Aycard Jean‐Pierre , Berger Jeanne , Bodot Hubert
Published: May 2005

Les spectres RMN du proton d'une série de R‐3 X‐4 cyclohexanone (d4‐2,2,6,6), cis et trans sons analysés. La comparaison des constantes de couplage vicinales avec celles des homologues cyclohexaniques conduit à préciser les équilibres conformationnels chaise‐chaise pour R = CH3, X = CN, la structure chaise des isomères cis avec un groupement t‐butyl équatorial et l'existence d'un équilibre conformationnel lorque les groupements (CH3)3C et CN sont trans. Cette dernière situation est analysée au moyen d'une relation de Karplus simplifiée, mais controlée, et dans l'hypothèse d'un mélange de deux conformères. Dans ces conditions, seuls peuvent être impliqués les conformères chaise diéquatorial et bateau (angle dièdre Φ34 de l'ordre de −6°C).
Structural studies on some 1,3,5,7‐tetraaza‐ and 1,3,5‐triazaadamantane derivatives
Authors: Farminer A. R. , Webb G. A.
Published: May 2005

1H and 13C NMR data are reported for hexamethylenetetramine (hexamine), 7‐nitro‐1,3,5‐triazaadamantane and some of their quaternary derivatives. INDO molecular orbital calculations have been performed on these molecules to aid the interpretation of their spectra.
Azobilirubin isomers: NMR structure determination using a shift reagent
Authors: Salmón Manuel , Díaz E. , Rock M. C. , Fenselau Catherine
Published: May 2005

The isomeric benzeneazodipyrromethene derivatives, obtained from the reaction of bilirubin and a phenyldiazonium salt were separated as their corresponding methyl esters. The lanthanide‐induced chemical shifts, coupling constants and double irradiation experiments permit direct assignment of methyl and vinyl substituent positions in these bilirubin‐derived isomers.
NMR spectral studies of quinoline derivatives. Long range 13C1H coupling constants in methylquinoline derivatives
Authors: Claret Paul A. , Osborne Alan G.
Published: May 2005

Long range 13C1H coupling constants are reported for a number of methylquinoline derivatives. The results have been compared with those observed in the pyridine series and correlated with 1H1H coupling constants.
NMR spectral studies: XIII—titanium tetrachloride‐induced and lanthanide‐induced shifts in the proton NMR spectra of β‐lactams
Authors: Bose Ajay K. , Manhas M. S. , Srinivasan P. R. , Chawla H. P. S. , Dayal B. , Foley D. A.
Published: May 2005

2‐Azetidinones which carry a proton each on C‐3 and C‐4 often pose a problem in the correct assignment of the resonances due to these protons; titanium tetrachloride has been shown to be an effective and reliable n.m.r. shift reagent to differentiate between these two protons on the basis of their different sensitivities to this reagent. A few compounds were also studied with Eu(fod)3 and Pr(fod)3 for the sake of confirmation.
The enol‐imine to keto‐enamine tautomerization involved in the formation of 3‐benzylamino‐5,5‐dimethylcyclohex‐2‐enone
Authors: Kikta E. J. , Bieron J. F.
Published: May 2005

The formation of 3‐benzylamino‐5,5‐dimethylcyclohex‐2‐enone has been found to proceed through the initial formation of its enol‐imine tautomer. The enol‐imine has been isolated by a novel synthesis. It involves suspending dimedone in hexane for one hour at 67 °C with the amine in solution. Nuclear magnetic resonance spectroscopy has confirmed the tautomerization by observing the changing spectra as the enol‐imine tautomerizes to 3‐benzylamino‐5,5‐dimethylcyclohex‐2‐enone. The change in the nuclear magnetic resonance spectra is highlighted by a moving peak, which proceeds upfield with decreasing intensity as the tautomerization reaches completion. This moving peak involves chelated water formed in the initial condensation of dimedone and benzylamine. The chelated water acts as an active exchange agent which enhances the tautomerization rate. Similar results are obtained for the Schiff base derived from dimedone and aniline. This is the first isolation of the pure enol‐imine tautomeric form of 3‐benzylamino‐5,5‐dimethylcyclohex‐2‐enone. Under refrigeration the enol‐imine is found to be stable for over six months.
The 13C NMR spectra of nine ortho‐substituted phenols
Authors: Smith William B. , Proulx Thomas W.
Published: May 2005

The 13C chemical shifts of nine ortho‐substituted phenols have been determined in cyclohexane and in dimethyl sulfoxide. All data were acquired in duplicate upon c.w. and FT instrumentation and both sets of data are presented.

The chemical shifts at carbons 1, 2 and 3 are correlated with the parameter Q. Q has been defined as P/Ir3 where P is the polarizability of the adjacent CX bond, I is the first ionization potential of the elements F, Cl, Br, I and H, and r is the CX bond length. Experimental values of Q are available for other substituents. The field and resonance parameters of Swain and Lupton may be combined with Q to form a three part multiple regression correlation which is more exact than that with Q alone and which applies to all carbons in the aromatic ring.

The results of this study suggest that only one value of the Q parameter is needed to characterize the behavior of the nitro group in these solvent systems. This conclusion is contrasted with earlier results of the effect of substituents on proton chemical shifts in these systems.
The reactions of transition metal chelates with organometallic compounds and their paramagnetic products: IV—the anion radical of acetylacetonate
Authors: Staško A. , Tkáč A. , Laurinc V. , Malík L.
Published: May 2005

The anion radical of acetylacetonate is formed by the reaction of nickel (II) acetylacetonate with Grignard reagents. From the two coupling constants found in the e.s.r. spectrum, the one of 2·6 G was assigned to the methine proton and the one of 12·5 G to the six equivalent methyl protons of acetylacetonate. The calculations of spin densities for the anion radical of acetylacetonate by the INDO method are in relatively good agreement with experiment.
Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms: XXXII—The 1H n.m.r. spectra and stereochemistry of 4‐aryl‐1,6,7,11b‐tetrahydro‐2H,4H‐[1,3]oxazino[4,3‐a]isoquinoline, 4‐aryl‐1,2,6,7,12,12b‐hexahydro‐4H‐[1,3]oxazino[3′,4′:1,2]pyrido[3,4‐b]indole and of related systems
Authors: Crabb Trevor A. , Mitchell Jacqueline S.
Published: May 2005

cis(4‐H,11b‐H)‐4‐Aryl‐1,6,7,11b‐tetrahydro‐2H,4H‐[1,3]oxazino [4,3‐a]isoquinoline and the related thiazino compound preferentially adopt in solution the O (or S) inside cis‐conformation in contrast to cis(1‐H,4a‐H)‐1‐arylperhydropyrido[1,2‐c][1,3]oxazine which adopts the trans fused conformation. 1‐(β‐Hydroxy‐ethyl)‐1,2,3,4‐tetrahydro‐β‐carboline condenses with benzaldehyde to give the 1,3‐oxazine derivative rather than the dimeric structure reported in the literature.
NMR–Untersuchungen an Dicyclopentadienderivaten: I—1H‐NMR: Anwendung von paramagnetischen Verschiebungsreagenzien (Eu(fod)3) zur Vereinfachung der Spektren exo/endo‐isomerer Diole
Authors: Kleinpeter E. , Kühn H. , Mühlstädt M.
Published: May 2005

Die Bestimmung der Stereochemie einer Reihe exo/endo‐isomerer 9.10‐Dihydro‐ bzw. Tetrahydrodicyclopentadien‐9.10‐diole (exo/exo bzw. endo/endo) unter Verwendung von Eu(fod)3 zur Auftrennung ihrer 1H‐NMR‐Spektren wird beschrieben. Die für halbmolares Verhältnis Eu(fod)3/Diol bestimmten Verschiebungswerte ΔEu gestatten dabei eine eindeutige stereochemische Zuordnung der Verbindungen. Die ΔEu‐Werte werden mit dem Abstand Hi…O‐Atom (Ri) korreliert.
Sur la tétrabromo‐2, 2, 6, 6 méthyl‐4 cyclohexanone: Mise en evidence d'un equilibre conformationnel par RMN à haut champ
Authors: Grenier‐Loustalot M. F. , Iratçabal P. , Lectard A. , Forchioni A.
Published: May 2005

La comparaison après simulation des spectres RMN à haut champ des tétrabromo‐2,2,6,6 méthyl‐4 et tertiobutyl‐4 cyclohexanones (1 et 2) nous a permis de mettre en évidence par l'étude des constantes de couplage, en particulier Jgem, Jea, Jaa et 4J et des déplacements chimiques que 1 présente à l'état dissous une isomérie de rotation.

Ce travail confirme les conclusions auxquelles nous avait conduits une étude par spectroscopie d'absorption dans l'infrarouge de 1 dans la région des vibrations de déformation δ(CH3).
Nuclear spin–spin coupling between 15N and 13C in an azomethine ylide and related compounds
Authors: Fritz Hans , Clerin Daniel , Fleury Jean‐Pierre
Published: May 2005

13C15N coupling constants of a stable azomethine ylide, a 2‐aza‐1,3‐diene and an O‐tosyloxime have been measured. The large one‐bond coupling constants (21·3 and 21·6 Hz) observed for the azomethine ylide prove the dipolar structure of this compound. For the other two compounds, two‐bond coupling constants are used to derive the stereochemistry at the C,N double bond.
a priori Calculations of molecular physical constants: II—an improvement in chemical shift calculations using a modified version of the CNDO/S method
Authors: Pouzard G. , Rajzmann M.
Published: May 2005

A modification is introduced into the CNDO/S method which takes into account electronegativity differences between atoms in a molecule. Results of 13C chemical shift calculations are largely improved by such a procedure with respect to those obtained using conventional CNDO/S wave functions.
Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para‐Phenylsubstituenten auf die Rotationsbarriere um die NB‐Bindung
Authors: Friebolin H. , Rensch R. , Wendel H.
Published: May 2005

Um den elektronischen Einfluß von Substituenten auf die freie Aktivierungsenthalpie der Rotation um die NB‐Bindung in Aminoboranen zu studieren, synthetisierten wir zwei Reihen von Verbindungen: (a) (CH3)2BCl(Phenyl‐p‐X) mit para‐Phenylsubstituenten am Boratom und (b) (p‐X‐Phenyl)CH3NB(CH3)2 mit para‐Phenylsubstituenten am Stickstoffatom der NB‐Bindung (X = NR2, OCH3, C(CH3)3, Si(CH3)3, H, F, Cl, Br, J, CF3 und NO2). Beim Vergleich der Rotationsbarrieren entsprechender Verbindungen beider Reihen ist ein entgegengesetzter Effekt des Substituenteneinflusses festzustellen:

Elektronenziehende p‐Phenylsubstituenten erhöhen ΔGc≠, wenn der Phenylkern am Bor steht, senken ΔGc≠ jedoch, wenn er am Stickstoff der NB‐Bindung gebunden ist. Elektronenspendende p‐Phenylsubstituenten zeigen das entgegengesetzte Verhalten.

Die Unterschiede der ΔGc≠‐Werte von substituierten und unsubstituierten Verbindungen [δ(ΔGc≠) = ΔGc≠(X) − ΔGc≠(X = H)] innerhalb jeder Reihe lassen sich gut mit den Hammett'schen σ‐Konstanten der entsprechenden Substituenten korrelieren, d.h. mit Hilfe induktiver und mesomerer Substituenteneinflüsse erklären.

Ein Vergleich der Steigungen der Korrelationsgeraden zeigt, daß diese Substituenteneinflüsse bei Verbindungen mit N‐Phenyl‐p‐X wesentlich stärker sind als bei solchen mit B‐Phenyl‐p‐X.
Aziridines N‐non substituées: XI—Inversion de l'azote dans des composes C‐substitués symetriquement ou non de part et d'autre du cycle
Authors: Martino R. , Lopez A. , Lattes A.
Published: May 2005

Le phénomène d'inversion de l'azote a pu être mis en évidence par RMN du proton dans un certain nombre d'aziridines NH diversement C‐substituées. Lorsque l'encombrement des deux faces du petit cycle est trop différent, un seul invertomère existe. A partir des différents déplacements chimiques et des constantes de couplages HCNH, on peut constater que l'invertomère privilégié, ou unique, est toujours celui pour lequel le proton NH est du côté du cycle le moins encombré. Pour les aziridines symétriques, la barrière d'inversion a été mesurée: elle est abaissée lorsque l'encombrement stérique augmente. Dans les dérivés C‐phénylés un facteur supplémentaire de stabilisation des invertomères apparaît, sans doute dû à des conformations préférentielles du cycle aromatique.
Proton magnetic resonance spectra of some 6‐ and 7‐substituted 2‐amino‐4‐hydroxypteridines
Authors: Storm Carlyle B. , Chung Hyang S.
Published: May 2005

The conformations in solution of 6‐phenyltetrahydropterin, 6,7‐diphenyltetrahydropterin and 6‐7, dimethyltetrahydropterin have been determined from their proton magnetic resonance spectra. The 6‐phenyltetrahydropterin has the reduced pyrazine ring in a half chair conformation with the phenyl ring in the equatorial position. Both the 6,7‐diphenyl‐ and 6,7‐dimethyltetrahydropterins are of the cis configuration and have one substituent in an axial position. The enzymatic activity of these cofactors may be related to these conformations.
Spin–spin couplings in doubly 15N labelled urea and 1,3‐dimethylurea
Authors: Stilbs P. , Forsén S.
Published: May 2005

The 1H n.m.r. spectra of doubly 15N labelled urea and 1,3‐dimethylurea have been analysed with the aid of computer simulation. 1H1H, 1H15N, 15N15N and 13C15N (from 13C Ft spectra) couplings are reported.
Hétérocycles contenant du phosphore: XXVII—Etude par Résonance Magnétique Nucléaire de quelques dérivés des dioxa‐et dithiaphospholanes‐1,3,2 monosubstitués en 4
Authors: Revel Monique , Roussel Jean , Navech Jacques , Mathis Ferdinand
Published: May 2005

Les spectres de RMN du proton d'une série de dérivés des méthyl‐4 (ou phényl‐4) dioxa‐ et dithiaphospholanes‐1,3,2 sont analysés. La configuration de ces composés est précisée. L'angle de torsion de la liaison C4C5 est calculée et la conformation du cycle à l'état dissous est proposée.
Study of the intermolecular Overhauser effect {1H}13C
Authors: Vandenbosch J. C. , Zimmermann D. , Reisse J.
Published: May 2005

The intermolecular Overhauser effect {1H}13C is studied on two binary systems chloroform/carbon disulfide and chloroform/acetone. Some comments are made concerning the use of these measurements for the study of intermolecular interactions in solution.
Carbon‐13 n.m.r. and CNDO/S study of 1,3‐indandione and heterocyclic analogues
Authors: Galasso Vinicio , Pellizer Giorgio , Le Bail Henri , Pappalardo Giuseppe C.
Published: May 2005

13C n.m.r. spectra are reported for 1,3‐indandione, phthalic anhydride, thiophthalic anhydride, and phthalimide in chloroform‐d solution. The 13C chemical shifts have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions; the agreement between theoretical and experimental values is improved when an empirical charge‐dependent term is added to the calculated diamagnetic and paramagneitc contributions.
Déplacements chimiques induits en RMN par un réactif lanthanidique: I—Application á l'analyse conformationnelle de sulfites cycliques
Authors: Cazaux Louis , Chassaing Gérard , Maroni Pierre
Published: May 2005

Les déplacements chimiques induits par Eu(fod)3 sur plusieurs séries de sulfites cycliques à six chaînons permettent de déterminer les paramètres Kc et ΔSR de l'équilibre de complexation pour une stoechiométrie supposée 1:1. La constante d'équilibre apparente Kc décroît lorsque la substitution en 4 et 6 et la polarité du substituant en 5 augmentent en relation avec une augmentation de la fréquence d'élongation vSO en infrarouge. Ainsi, le groupe SO ax s'associera plus fortement que SO éq. Lorsqu'un équilibre conformationnel existe en l'absence de réactif lanthanidique, on peut prévoir qu'il évoluera avec lui vers une forme à SO ax. L'exploitation des ΔSR à l'aide de l'équation de pseudocontact confirme ces prévisions: (i) les formes chaises à SO ax sont stabilisées; (ii) les chaises à SO éq avec deux substituants éq en 4 et 6 présentent un équilibre avec quelques pourcents de conformation flexible à SO ax, surtout en l'absence de substituant ax en 5; (iii) les formes croisées d'axe 2–5 à SO intermédiaire et t‐Bu trans en 4 et 6 évoluent vers un bateau à O en proue et SO ax; (iv) le t‐Bu‐5 oxo‐2 dioxathianne‐1,3,2 trans, chaise à t‐Bu et SO axiaux pour ⋍70%, a son équilibre conformationnel complètement déplacé vers cette forme; (v) le triméthyl‐4,4,6 oxo‐2 dioxathianne‐1,3,2, cis, équilibre où interviennent les trois types de SO, s'associe essentiellement en conformation croisée d'axe 1–4 et à groupe SO ax. La plupart de ces résultats ont été étayés par l'analyse des constantes de couplage pour le rapport R0/S0 = 1.
Calculation of carbon‐13 n.m.r. shielding constants of carbocations
Authors: Bernstein Thomas , Geschke Dieter
Published: May 2005

Carbon‐13 n.m.r. shielding constants of isobutene molecules and t‐butyl carbenium ions are calculated using the NDDO quantum chemical approximations. The theoretical resonance shifts between corresponding nuclei of the two structures are compared with experimental values published by Olah et al. The results are discussed with respect to excitation energies which are obtained including Fischer‐Kollmar‐parametrization.
Etude par RMN 1H d'hétérocycles voisins de l'oxazaphospholane‐1,3,2: III—Le phényl‐1 dioxa‐2,8 aza‐5 phosphav‐1 bicyclo[3.3.0]octane et le dioxa‐1,6 diaza‐4,9 phosphav‐5 spir[4.4]nonane
Authors: Devillers Jean , Houalla Doureid , Roussel Jean , Wolf Robert
Published: May 2005

L'interprétation, en termes d'analyse conformationnelle, des paramètres de RMN 1H obtenus pour le phényl‐l dioxa‐2,8 aza‐5 phosphav‐1 bicyclo[3.3.0]octane, conduit à proposer pour chacun des cycles pentagonaux une forme enveloppe bloquée, l'atome d'azote étant plan. La même analyse appliquée au dioxa‐1,6 diaza‐4,9 phosphav‐5 spiro[4.4]nonane, montre que le cycle oxazaphospholane est le siège de mouvements de libration autour de la liaison CC.
Lanthanide reagent effects on 3‐(2′,4′‐dimethylphenyl)‐1H,3H‐quinazoline‐2,4‐dione
Authors: Buti M. , Vigne C. , Montginoul C. , Torreilles E. , Giral L.
Published: May 2005

We report an analysis of the europium‐shifted n.m.r. spectrum of 3‐(2′,4′‐dimethylphenyl)‐1H,3H‐quinazoline‐2,4‐dione and the resonance assignment of most of its protons.
Analyse RMN (1H, 13C, 31P) de méthoxy‐2 dioxaphospholanes‐1,3,2 di‐ et tétraméthylés en position 4 et 5
Authors: Pouchoulin G. , Llinas J. R. , Buono G. , Vincent E. J.
Published: May 2005

L'étude en RMN du 1H, 13C et 31P d'hétérocycles dioxaphospholaniques a permis d'identifier sans ambiguité la position des substituants sur le cycle et aussi d'accéder à un certain nombre d'informations relatives à la stéréochimie de la molécule.
Radikale aus Polymethin‐Farbstoffen: III—Polymethinoxonole
Authors: Oehling H. , Baer F.
Published: May 2005

Die ESR‐Spektren von Neutralradikalen in Lösung, erzeugt durch elektrolytische Reduktion einer Reihe dinuclearer Polymethinoxonole, werden interpretiert. Auf Grund der Werte der ESR‐Kopplungskonstanten, von 1H‐NMR‐Messungen und HMO‐Rechnungen werden Konformation, π‐Elektronendichte‐verteilung und CC‐Bindungslängen bei diesen Radikalen diskutiert.
19F n.m.r spectra of heptafluoroisoquinoline and hexafluoro‐1‐methoxyisoquinoline. Long‐range inter‐ring coupling constants
Authors: Matthews R. S.
Published: May 2005

An analysis of the 19F n.m.r. spectra of heptafluoroisoquinoline and hexafluoro‐1‐methoxyisoquinoline is presented. As in heptafluoroquinoline, the inter‐ring FF coupling constants alternate in sign and magnitude and are positive over an odd number of bonds. They correlate with SCFMO carbon–carbon polarizabilities and this infers that the long‐range coupling mechanism is dominated by the contribution from the π‐electron system.
A comment on the interpretation of 13C n.m.r. δ‐syn‐axial substituent effects in cyclic molecules
Authors: Engelhardt G. , Jancke H. , Zeigan D.
Published: May 2005

An alternative explanation for δ‐syn‐axial substituent effects of 13C chemical shifts is given using the concept that the δ‐syn‐axial interaction in the substituted compound replaces the γ‐gauche interaction in the parent molecule. The application of this principle to substituted norbornanes and steroids leads to the conclusion that the ‘net steric’ δ‐syn‐axial shift is upfield rather than downfield.
Long range 13C shift effects (δ and ϵ) in methylcyclohexanes
Authors: Vierhapper Friedrich W. , Willer Rodney L.
Published: May 2005

13C n.m.r. spectra of a number of methyl substituted cyclohexanes, some of them conformationally homogeneous, have been recorded in CDCl3 and used to determine shift effects engendered by the introduction of methyl groups on carbon atoms remote from the site of substitution. Sizeable changes in shifts are found, including a substantial effect of an equatorial methyl group on an axial methyl group δ to it (+0.67 ppm, ‘δea’). The effects reported are of consequence in investigations of conformational problems by 13C n.m.r. techniques.
13C n.m.r. spectra of some pyrylium salts and related compounds
Authors: Balaban A. T. , Wray V.
Published: May 2005

The 13C chemical shifts of several alkyl and phenyl substituted pyrylium perchlorates, together with related pyridine and pyridinium salts, are reported. The shifts in the isoelectronic series benzene, pyridine, pyrylium cation correlate well with charge densities calculated by INDO MO theory. Charge densities also account for the shift changes found at C‐3, C‐4 and C‐5 for protonation of pyridine and 2,4,6‐trimethylpyridine. The shift changes observed on protonation for C‐2 and C‐6, along the series pyridine, 2,4,6‐trimethylpyridine and 2,4,6‐triphenylpyridine can only be rationalized by consideration of both charge density and π‐bond order changes. The effects of alkyl substitution on the shifts of the pyrylium cations are not accounted for by charge density changes. Empirical correlations of these shifts with literature data for the alkylbenzenes and the shifts of the phenyl substituted 6‐membered heterocycles are discussed.
Peak suppression in Fourier transform n.m.r.: Application of the selective excitation technique to the problem of 13C satellites in 31P resonance
Authors: Harris R. K. , Newman R. H. , Okruszek A.
Published: May 2005

Selective pulsed excitation was used in a technique to suppress the resonance due to a per‐12C‐isotopomer so as to overcome dynamic range problems when observing ‘13C satellite’ lines. The technique was used to obtain nuclear spin parameters from the 13C satellites in 31P resonance for the racemic isomer of P,P′‐dimethyl‐P,P′‐diphenyldiphosphine disulphide, [MePhP(:S)]2.
1H n.m.r. investigation on the site of hydration in the asymmetric diazanaphthalenes
Authors: van de Weijer Peter , Meer Douwe van der
Published: May 2005

The site of hydration for 1,6‐ and 1,7‐naphthyridine has been determined by specific line broadening in the 1H n.m.r. spectra on the addition of water. The site of hydration appears to be the same as the site of protonation (β‐nitrogen atom). The site of hydration in quinazoline has been shown to be the α‐nitrogen atom. This strongly indicates that the site of protonation in this compound will also be at that nitrogen.
The rα‐structure of partially oriented m‐dichlorobenzene as determined from its proton magnetic resonance spectrum including the carbon–13 satellites
Authors: Diehl P. , Bösiger H.
Published: May 2005

The proton spectrum, including 13C satellites at natural abundance, of partially oriented m‐dichlorobenzene was analysed. Carbon–carbon, carbon–hydrogen and hydrogen–hydrogen internuclear distance ratios, as well as bond angles were derived and corrected for harmonic vibrations (rα‐structure).
13C shieldings of several diacetylenic alcohols
Authors: Hearn Milton T. W.
Published: May 2005

The 13C spectra of several conjugated diynols and symmetrical diynediols, represented by the parent compounds 2,4‐pentadiyn‐1‐ol and 2,4‐hexadiyne 1,6‐diol, respectively, have been determined and individual resonances assigned. The data show close similarities to those observed with related 2‐yn‐1‐ols. Mutual shielding interactions between the conjugated triple bonds result in upfield shifts of both the α‐ and β‐sp‐hybridized carbon nuclei by c. 4.5 ppm, relative to the ethynyl prototype. The deshielding γ effect induced by the hydroxyl group at the interior sp‐hybridized carbons is discussed.
Nuclear magnetic resonance of oriented molecules in lyotropic liquid crystalline media: Pyridine, 4‐cyanopyridine and benzonitrile
Authors: Long Robert C. , Goldstein J. H.
Published: May 2005

Proton distance ratios for pyridine, benzonitrile and 4‐cyanopyridine have been obtained in a potassium laurate lyotropic mesophase and compare favorably with values for different thermotropic solvents. Order matrices indicate a preference for the C2v symmetry axis of the molecules to be aligned along the optical axis of the mesophase.
Unusual temperature effects on the non‐equivalence of geminal methyl groups
Authors: Jennings W. Brian , Al‐Showiman Salim , Tolley Malcolm S. , Boyd Derek R.
Published: May 2005

The geminal anisochronism (Δδ) of the isopropyl methyl groups in the 1H n.m.r. spectrum of N‐[2‐methyl‐1‐(1‐naphthyl)propylidene]benzylamine showed unusually pronounced temperature and solvent effects. It is noteworthy that both accidental and dynamic equivalences were encountered. Slow rotation around the naphthyl–imino bond is responsible for the diastereotopic nature of the geminal methyl groups, and possible reasons for the temperature and solvent effects are considered. Surprisingly, the temperature effect was not reflected in the 13C anisochronism of the methyl carbon nuclei. These observations underline the need for caution in drawing firm conclusions from variable temperature studies on geminal non‐equivalence.
The additivity of substituent effects upon J(FF) in polysubstituted fluorobenzenes: An update
Authors: Wray Victor , Lincoln David N.
Published: May 2005

Substituent effects upon 3J(FF) are demonstrated to be additive, and a previous analysis of 4J(FF) and 5J(FF) in polysubstituted fluorobenzenes is updated.
Aufspaltungseffekte höherer Ordnung in 1H‐CW‐off‐resonance‐entkoppelten 13C‐NMR‐spektren
Authors: Radeglia R.
Published: May 2005

Zusätzliche Aufspaltungen, die durch Effekte höherer Ordnung in 1H‐off‐resonance‐entkoppelten 13C‐NMR‐Spektren hervorgerufen werden, können mit Hilfe eines einfachen Modells abgeschätzt werden.
Effects of simultaneous 13C1H and 13C11B decoupling on the carbon‐13 n.m.r. spectra of some organoboron compounds
Authors: Mazurek M. , Mallard T. M. , Gorin P. A. J.
Published: May 2005

13C FT n.m.r. spectra were obtained from borates of methyl α‐D‐glucopyranoside, triethylboron, sodium tetraphenylboron and 1‐butaneboronic acid employing a simultaneous 1H and 11B decoupling network. The effectiveness of the system was evident using the three latter organoboron compounds. Since no diminution in line broadening of signals occurred in the spectrum of the sugar borate, the absence of 13CO11B coupling was indicated. This finding was confirmed by comparing the effects of varying the temperatures of sugar borates and triethylboron on their conventional 13C n.m.r. spectra.
Carbon‐13 nuclear magnetic resonance spectroscopy of polychlorinated diphenyl ethers
Authors: Edlund Ulf , Norström Åke
Published: May 2005

Carbon‐13 n.m.r. chemical shifts are reported for diphenyl ether and several of its chlorinated analogs. Carbon shieldings were found to be dependent on the degree of steric interference to conjugative release by the oxygen atom. Substituent effects due to attached chlorine atoms seem to be more easily transmitted into the adjacent aryl moiety if the number of ortho chlorines is reduced. These results were clearly seen by a variable‐by‐variable plot display or by using a pattern recognition computer program. Spin‐lattice relaxation times have been measured for several compounds mainly for assignment purposes, but they are also briefly discussed in view of possible interconversion mechanisms.
Carbon‐13 nuclear magnetic resonance spectra of some aromatic diterpenoids
Authors: Nishida Toshiaki , Wahlberg Inger , Enzell Curt R.
Published: May 2005

13C n.m.r. studies of a series of tricarbocyclic ring C aromatic diterpenoids using proton‐noise and single‐frequency off‐resonance decoupling, partially relaxed Fourier transform techniques, shift reagents and specifically labelled derivatives have permitted unequivocal assignments of almost all signals. The shieldings caused by oxygenation of C‐18 and C‐19 and by introduction of various substituents in the aromatic ring are discussed. It is concluded that the 13C n.m.r. data are sufficiently characteristic to allow stereochemical assignments. Some effects of deuterium substitution on the carbon resonances are presented.
The proton magnetic resonance spectra of some disubstituted acetophenones
Authors: Batts B. D. , Pasaribu S. J. , Williams L. R.
Published: May 2005

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H‐6 is adjacent to the acetyl methyl group whilst the 3,4‐disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H‐6 proton is adjacent to the carbonyl group.
13C n.m.r. spectra of lysergic acid derivatives: II—dihydrolysergamides
Authors: Zetta L. , Gatti G.
Published: May 2005

The conformations of dihydrolysergamides and 10‐methoxydihydrolysergamides have been inferred from the study of the chemical shifts of the amide hydrogens and their temperature dependence. The 13C chemical shifts have been shown to be sensitive to conformational changes of the piperidine ring. The results indicate that the conformation of the latter depends both on the substituent in position 10 and on the solvent.
Steric effects in 29Si and 13C n.m.r. spectra of trimethylsiloxy‐substituted benzenes
Authors: Schraml J. , Chvalovský V. , Jancke H. , Engelhardt G.
Published: May 2005

29Si and 13C NMR spectra of trimethylphenoxysilane and three bis(trimethylsiloxy)benzenes have been investigated. Crowding in the ortho derivative leads to a small but observable deshielding of both silicon and carbon nuclei of the trimethylsiloxy group. In comparison to analogous effects observed in trimethylsilyl‐substituted benzenes the oxygen link appears to increase the susceptibility of silicon to this steric effect but to decrease that of the methyl carbons. It is suggested that the operative steric interaction might not be that between the terminal methyl groups but involves the oxygen atom.
Steric gamma effect on 29Si shielding in (CH3)3SiOCR groups
Authors: Engelhardt G. , Schraml J.
Published: May 2005

It is shown that a γ‐methyl group causes approximately a 3 ppm upfield shift of the silicon resonance in (CH3)3SiOCCH3 fragments. It is estimated that polar effects contribute about 0.8 ppm to this shift leaving a net steric γ upfield shift of 2 ppm. Variations around these average values are interpreted by different conformer populations, the importance of which are illustrated by the shifts in trimethylsiloxy derivatives of adamantane.
Calculation of some 13C nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A.
Published: May 2005

13C screening constants and their anisotropies are calculated within the CNDO/S framework by using gauge dependent atomic orbitals in the molecular orbital description. The calculations include the excited singlet states which are mixed with the ground state by an external magnetic field. Reasonable agreement with available experimental data is obtained in most cases. Comparisons with some ab initio results are also made.
Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R‐3 et R‐5 cyano‐4 cyclohexènes deutériés (R=méthyl ou t‐butyl)
Authors: Lafrance Ronald , Aycard Jean‐Pierre , Bodot Hubert
Published: May 2005

Pour les R‐3 et R‐5 acétoxy‐1 cyano‐4 cyclohexène D2‐6,6 trans, les fractions molaires des conformères diéquatoriaux ont été évaluées: 0,83 (méthyl‐3), 0,68 (méthyl‐5), 0,57 (t‐butyl‐3) et 0,55–0.69 (t‐butyl‐5). Pour les deux derniers composés, les valeurs des constantes de couplage sont compatibles avec l'hypothèse d'équilibres ee⇄aa. Pour les isomères cis, les conformères à groupement alkyle équatorial sont prédominants (fraction molaire 0,76 pour méthyl‐3 et méthyl‐5) ou exclusifs (t‐butyl‐3‐butyl‐5). Par contre, l'acétoxy‐1 t‐butyl‐3 méthoxycarbonyl‐45 cyclohexène cis présente une hétérogénéité conformationnelle. L'enthalpie libre conformationnelle du groupement méthyle en position 4 est évaluée à −0,6 kcal mol−1 (2,5 kJ mol−1).
The reactions of transition metal chelates with organometallic compounds and their paramagnetic products. V—New possibilities in the generation of anion radicals by reactions of Grignard reagents and lithium alkyls in the presence of transition metal ions
Authors: Staško A. , Malík L. , Tkáč A. , Adamčík V. , Hronec M.
Published: May 2005

In the reactions of Grignard reagents and n‐butyllithium the presence of transition metals and complexing solvents facilitates the formation of anion radicals. High radical concentrations, observable for some days at laboratory temperature, and very well resolved e.s.r. spectra of the following structural types have been obtained using a relatively simple procedure: aromatic hydrocarbons, heteroaromatics, aldehydes, ketones, α‐diketones, enolates of β‐diketones, quinones, sulphones, sulphoxides, nitro‐, nitroso‐ and azo‐benzenes, cyano compounds and phosphine oxides. It is suggested that the transition metals, according to the type of reactants and the experimental conditions, mediate the transfer of one electron to the substrate in many reactions and stabilize the intermediate products as anion radicals. The variation of solvents and organometallic compounds modifies the reduction power of such systems and leads to the radical products in a different reduction state. The procedure described is advantageously employable in the generation of anion radicals, and the effect of transition metals which has been found may widen the scope of this phenomenon to many different applications.
The gear effect. VII—Conformational analysis of methyl N,N‐diisopropylcarbamate, its thiol and diseleno analogues. An experimental proof for a two‐step conformational interconversion mechanism
Authors: Liljefors Tommy , Sandström Jan
Published: May 2005

The conformations of the isopropyl groups and the barriers to conformational interconversion in methyl N,N‐diisopropylcarbamate, its thiol and seleno analogues have been studied by 1H d.n.m.r. In the diselenocarbamate, complete bandshape analysis of the Se‐methyl proton signals proves unequivocally that the conformational interconversion takes place by rotation of one isopropyl group at a time rather than by a concerted rotation of both groups. The populations and barriers observed for the new compounds fit well into the general scheme found previously for other N,N‐diisopropylamides and ‐thioamides.
Group IVB organometallic compounds of furan: 13C, 29Si and 119Sn n.m.r. Spectra
Authors: Mägi M. , Lippmaa E. , Lukevics E. , Erĉak N. P.
Published: May 2005

The 13C, 29Si and 119Sn chemical shifts of 2‐ and 2,5‐substituted organometallic (M=C, Si, Ge, Sn, Pb) derivatives of furan were measured. The most important factors, determining the specific features of the studied spectra, are d‐orbital availability and atomic radius of the central atom M, as well as the relatively higher (as compared with benzene) energies of the π‐electron energy levels of the furan ring.
Behinderte Rotationen um CC‐ und CN‐Bindungen in Enaminothioketonen mit verschiedenen N‐Substituenten
Authors: Kleinpeter E. , Pulst M.
Published: May 2005

In einer Reihe 1,2‐Diphenyl‐enaminothioketone werden behinderte Rotationen um CN‐ und CC‐Bindungen beobachtet. Die freien Aktivierungsenthalpien ΔG≠ dieser dynamischen Prozesse werden bestimmt und hinsichtlich Delokalisierung des freien Elektronenpaares am Stickstoff der verschiedenen Aminogruppen sowie deren Basizität diskutiert.
N.m.r. spectra of cyclic amines. II—Factors influencing the chemical shifts of α‐protons in aziridines
Authors: Breuer Eli , Somekh Lila , Ringel Israel
Published: May 2005

Proton magnetic resonance spectra of trans and cis‐2,3‐diphenylaziridine (1 and 2) and their N‐ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene‐d6 at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N‐ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the 1H n.m.r. spectra of 1–4 in deuterochlorofom‐trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N‐alkylaziridines the effect of the N‐alkyl group predominates.
Theoretical nuclear spin–spin coupling constants using atom–atom polarizabilities. 13CH and HH′ coupling constants of some [2.2.1] bicyclic compounds using the INDO approximation
Authors: Joela Heikki
Published: May 2005

Theoretical nuclear spin–spin coupling constants are calculated using mutual and self atom–atom polarizabilities according to a theory where no semi‐empirical parameters are used, except Slater exponents which can be obtained from other sources. As an application, the 13CH and HH′ couplings of some [2.2.1] bicyclic compounds are calculated with the aid of INDO molecular orbitals and compared with the experimentally obtained coupling constants.
Nuclear magnetic resonance studies on some cyclic esters containing the t‐butyl group
Authors: Hellier Desmond G. , Webb Frederick J.
Published: May 2005

The high resolution proton magnetic resonance spectra of a series of cyclic inorganic esters and analogous 1,3‐dioxans have been analysed. The coupling constants and chemical shifts involved indicate that most of the compounds exist preferentially in a chair form.
Structural studies by 1H and 13C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R1C(O)CHCHNR2R3
Authors: Kozerski Lech
Published: May 2005

13C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O‐protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1C–2 and C–3N bonds discernible at room temperature. O‐protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the 13C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.
A back‐of‐the‐envelope algorithm for the analysis of ABX systems
Authors: Borremans Frans , Tavernier Dirk
Published: May 2005

It is shown that one of the two conjugate solutions compatible with the AB part of an ABX system can easily be eliminated, at an early stage of the analysis, by considering intensity ratios in the X region.
Silicon‐29 and carbon‐13 n.m.r. studies of organosilicon chemistry. VII—trimethylsilylated silicates
Authors: Harris R. K. , Newman R. H.
Published: May 2005

Silicon‐29 n.m.r. was used to study the products from trimethylsilylation of minerals. Chemical shifts are reported for four model compounds, viz. the monomer, dimer, linear trimer (from natrolite) and cyclic tetramer (from laumontite). Information is then obtained from the products of trimethylsilylation of the anhydrous calcium silicates wollastonite and pseudo‐wollastonite. In the latter case it is shown that the principal products are the four model compounds, and percentage yields are obtained for these.
Silicon‐29 and carbon‐13 n.m.r. studies of organosilicon chemistry. VIII—Assignment of the 29Si and related 1H resonances of trimethylsilylated sugars by deuteration and shift reagent studies
Authors: Haines Alan H. , Harris Robin K. , Rao Renée C.
Published: May 2005

Two techniques were investigated for assigning the 29Si n.m.r. spectra of trimethylsilylated sugars. Specific deuteration, together with selective proton decoupling experiments, has allowed the complete assignment for methyl 2,3,4,6‐tetra‐O‐trimethylsilyl‐α‐D‐glucopyranoside. Double resonance spectra obtained in the presence of a lanthanide shift reagent, Pr(dpm)3, have enabled the 29Si and 1H signals for the ‐SiMe3, groups of methyl 2,3,4‐tri‐O‐trimethylsilyl‐α‐D‐glucopyranoside, to be linked. A complete and unambiguous assignment of the 29Si spectrum for this molecule was obtained by selective deuteration, thus giving an unequivocal assignment of the –SiMe3 proton resonances also. Definitive data regarding the effects of Pr(dpm)3 on the 29Si and 1H resonances of the various –SiMe3 groups of methyl 2,3,4‐tri‐O‐trimethylsilyl‐α‐D‐glucopyranoside are therefore available.
Radikale aus Polymethin‐Farbstoffen. IV—Dikation‐Radikale aus Polymethincyanin‐Farbstoffen mit Indolenin‐Endgruppen
Authors: Oehling H. , Baer F.
Published: May 2005

Durch elektrolytische Oxidation konnten aus dinuklearen Polymethincyanin‐Farbstoffen Dikation‐Radikale erzeugt werden. Ihre ESR‐Spektren bestätigen die erwartete Struktur der Radikale.
Benzo‐ and indolo‐quinolizine derivatives XI—The configurational and conformational study of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f]phenanthridine isomers by 270 MHz 1H n.m.r.
Authors: Van Binst G. , Laus G.
Published: May 2005

The preferred conformations of the four isomers of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f] phenanthridine have been determined by 270 MHz 1H n.m.r. and i.r. spectroscopy. N.m.r. assignments are based on the specific chemical shifts of the protons adjacent to the nitrogen atom, their geminal coupling constants and on the shifts induced by the CC bonds and by the benzene nucleus. Specifically deuterated derivatives and double resonance experiments confirm the assignments unequivocally. These data are completed by solvent and temperature studies.
Calculations of the 13C nuclear screening tensors for coumarin and some methoxycoumarins
Authors: Grigor G. I. , Webb G. A.
Published: May 2005

INDO calculations are reported of the 13C nuclear screening tensors in coumarin and some of its methoxy derivatives. Calculations based upon a linear combination of gauge dependent atomic orbitals and those using an uncoupled Hartree–Fock approach are described. Comparison with the results of less sophisticated calculations shows that changes in the excitation energies, bond orders and the 〈r−3〉2p term are together responsible for determining the 13C chemical shifts.
Analysis of the Vorontsova equation for calculation of vicinal coupling constants: Criticism of the criticism of the Karplus equation
Authors: Jankowski Krzysztof , Rabczenko Andrzej
Published: May 2005

Analysis of the Vorontsova calculation of vicinal coupling constants in terms of angular and chemical shift dependence indicates some serious inconsistencies in this equation.
An 1H n.m.r. study of complexation and self‐association processes in the ternary system: tert‐butyl alcohol–acetone–cyclohexane
Authors: Balevichius V. , Kimtys L.
Published: May 2005

The hydroxyl proton chemical shifts of tert‐butyl alcohol, dissolved in acetone and in binary mixtures of acetone with cyclohexane, have been measured as functions of concentration at temperatures of 20, 35, 50 and 60 °C. Using both the equilibrium constant and the quasi‐lattice methods for the interpretation of experimental data, the thermodynamic parameters of self‐association and complexation have been determined, and their dependences on the solvent composition have been analysed. The chemical shifts of the hydroxyl proton obtained in the complexes and the thermodynamic parameters of complexation of tert‐butyl alcohol with acetone‐d6 proved to be the same as for the tert‐butyl alcohol–acetone system.
Effect of substituents on the 1H n.m.r. spectra of para‐disubstituted benzenes. A graphical aid in the correct assignment of chemical shifts
Authors: Holík Miroslav
Published: May 2005

In para‐disubstituted benzenes, the effect of one substituent is transferred to the other composite substituent group and its decreased influence on the ortho and meta protons is reflected in their chemical shifts. A graphical presentation of this linear non‐additive dependence can serve as an aid in the correct assignment of the corresponding aromatic region of the spectra. The method is demonstrated on two series of chemical shift data taken from the literature.