Geminal coupling constants in methylene groups

Can. J. Chem. 55,3456 (1977). The conformational properties of seven 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctenes bearing substituents at C-6 have been studied using variable temperature proton nmr spectroscopy. The position of the equilibrium between boat-chair (BC) and twist-boat (TB) conformers has been measured in several solvents. In contrast to the unsubstituted dibenzocyclooctene, appreciable amounts of TB conformer are present when C-6 is substituted by alkyl, hydroxy, or cyano substituents. Measurements at different temperatures showed the TB form to possess the greater entropy. Barriers to the BC + TB interconversion were determined by coalescence studies, using both approximate and complete line shape methods. Barriers ranged from 10.1 kcal/mol for the 6-keto derivative to 16.7 kcal/mol for the 6-hydroxy-6-methyl derivative. Chem. 55,3456 (1977). ROGER N. RENAUD, JOHN W. BOVENKAMP, ROBERT R. FRASER et JEAN-LOUISOn etudie, par resonance magnktique du proton (rmn) et variant la temperature, les propriktts conformationnelles de sept tetrahydro-5,6,7,12 dibenzo[a,d]cyclooctenes ayant des substituants en C-6. La position de l'tquilibre entre les conformeres chaise-bateau (CB) et bateau-crois6 (BC) est mesuree dans plusieurs solvants. Contrairement au dibenzocyclooctene non substitue, une quantite appreciable de conformeres (BC) est prtsente lorsque le C-6 est substitue par un groupe alkyle, hydroxy ou cyano. Les mesures a differentes temperatures montrent que la forme BC possede une plus grande entropie. Les barrieres d'interconversion CB + BC sont dttermintes par des etudes de coalescence en utilisant les methodes approximatives et completes basees sur la forme des courbes. Les barrieres s'ktalent de 10.1 kcal/mol pour le derivt cCto-6 a 16.7 kcal/mol pour le derive hydroxy-6 methyl-6.[Traduit par le journal] I n the past few years the dibenzocycloocta-1,4-diene3 ring system l a has attracted considerable interest regarding its conformational properties. The first evidence on this topic came from a 'H nmr study of compounds related to la, specifically the azocines 2a-f (1, 2). Subsequently studies on a variety of other heterocyclic analogs 3a-1 were reported (3) and, most recently, the conformational properties of the hydrocarbon l a itself have been described (4). The parent compound, 1,4-cyclooctadiene, has been the subject of analysis by I3C and 'H tech-'NRCC No. 16120. 2Present address: Defence Research Establishment Ottawa, Ottawa, Ont., Canada KIA 024.3The eight-membered ring l a , whose correct name is 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctene, has the numbering shown in formula 1. This numbering is employed throughout the paper. niques (5) as well as by strain energy or force field calculations (5, 6). In this paper we wish t o describe the elucidation of the conformational properties of a series of dibenzocyclooctadiene derivatives lb-h (7) by the use of 'H nmr techniques. For personal use only.

Section: A Criteria For Assignment Of Conformationsupporting

confidence: 59%

Conformational study of a series of 6-substituted 5,6,7,12-tetrahydrodibenzo[a,d]-cyclooctenes by nuclear magnetic resonance spectroscopy

Renaud¹,

Bovenkamp²,

Fraser³

et al. 1977

“…En les comparant avec celles dCterminCes par Corse et al Hz du couplage 2J2,-2, est plus grande que celle observCe habituellement dans cette sCrie. Elle pourrait itre interprttke par un aplatissement de la forme chake au niveau de l'enchainement C1-C2-C3 qui a Ct C reconnu comme responsable de l'augmentation d'une telle constante (17). Cette d~formation serait Cgalement responsable du fait que le proton H2a rCsonne a champ plus faible que H2e, ce qui constitue une inversion de la rkgle de Lemieux (18).…”

Section: Resultats Et Discussionunclassified

Étude conformationnelle et structurale de 1,5-diacétoxy-3,4-bis(bicyclophosphoranylato)quinate de méthyle

Baltas¹,

Chahoua²,

Gorrichon³

et al. 1991

In connection with our work on quinic acid derivatives, which are supposed to regulate the biosynthesis of aromatic amino acids, we have prepared the methyl 1,5-di-O-acetyl-3,4-bis-O-(bicyclophosphoranylato)quinate 7. The compound obtained has been characterized by NMR (1H and 31P), IR, elemental analysis, and mass spectrometry. Its molecular structure has been determined by X-ray diffraction and an exhaustive conformational study has been accomplished. The quinic ring adopts an almost perfect chair form. Both bicyclophosphoranyl groups present a trigonal bipyramidal geometry with an axial–equatorial–axial type annelation. The pentagonal rings adopt an envelope form in which the tetrasubstituted carbon atom is at the top of the fold. Key words: shikimic acid pathway, methyl 1,5-di-O-acetyl-3,4-bis-O-(bicyclophosphoranylato)quinate, conformational analysis, 1H and 31PNMR, crystal structure.

“…It seems reasonably well established that the magnitude of a geminal lI-9-'H coupling depends upon the relative orientation of an oxygen substituent attached to an adjacent carbon (2,3,(18)(19)(20)(21)(22). It is thus of relevance that the 6,,6, couplings of the D-gluco derivatives are larger (less negative) than those of the L-ido derivatives.…”

Section: Discussionmentioning

confidence: 99%

Studies of specifically fluoridated carbohydrates. Part V. Derivatives of 3,6-anhydro-5-deoxy-5-fluoro-1,2-O-isopropylidene-α-L-idofuraeose

Hall¹,

Steiner²

1970

The facile synthesis of 3,6-anhydro-5-deoxy-5-fluoro-1,2-O-isoprcpylidene-cc-~-idofuranose (4) from readily available precursors is described. The 'H and 19F nuclear magnetic resonance spectra of this derivative have been analyzed. Interestingly, the fluorine substituent exhibits detectable spin coupling with all ring protons except H-2. Both of the anomeric 1,2-di-0-acetyl derivatives of (4) IntroductionWe have previously described (2, 3) studies of pyranosyl fluoride derivatives which illustrate the potential which fluorine nuclear magnetic resonance (19F n.m.r.) spectroscopy has as a sensitive "probe" for studying pyranose derivatives. In order to apply the "F n.m.r. technique to the more difficult problems associated with furanose systems, it was felt necessary to have previously studied some derivatives having reasonably defined conformations. The 3,6-anhydro-1,2-0-isopropylidene-hexofuranose system (1, 2) seemed admirably suited for this purpose. Earlier proton magnetic resonance (p.m.r.) studies (4) had shown the conformation of this system to be relatively insensitive to changes in the nature of the ring substituents. Thus, as far as is possible for a furanose derivative, this would appear to be a conformationally "rigid" system.