Molecular asymmetry in sugar derivatives

1975 ◽  
Vol 28 (3) ◽  
pp. 687 ◽  
Author(s):  
RE Gall ◽  
L Tarasoff
Keyword(s):  
Coupling Constants ◽  
Hydrogen Atoms ◽  
Vicinal Coupling Constants ◽  
Molecular Asymmetry ◽  
Sugar Derivatives ◽  
Derivatives Of

The N.M.R. spectra of a series of derivatives of the four trihydroxyglutaric acids (1)-(4) have shown non-equivalence of the hydrogen atoms attached to C 2 and C 4 in the D- and L-arabino series (3) and(4) which is not observed in the derivatives of symmetrical D- ribo and D-xylo acids (1) and (2). Vicinal coupling constants have led to predictions regarding the major conformations.

Conformational Studies on 1,3-Dioxepanes. Part IV. Applications of Geminal Coupling Constants to Conformational Analysis of 1,3-Dioxepanes

1974 ◽  
Vol 52 (24) ◽  
pp. 4062-4071 ◽  
Author(s):  
T. Bruce Grindley ◽  
Walter A. Szarek
Keyword(s):  
Conformational Analysis ◽  
Coupling Constants ◽  
Conformational Studies ◽  
Vicinal Coupling Constants ◽  
Geminal Coupling ◽  
Derivatives Of ◽  
Acetal Carbon

The magnitude of —OCH2O— group geminal H,H coupling contants, the size of the vicinal coupling constants, and the tenets of conformational analysis were used to establish that in solution the conformation of the 1,3-dioxepane rings in derivatives of 1,3:2,5-di-O-methylenemannitol and 2,5-O-methylenemannitol is predominantly the twist-chair in which the C2 axis passes through the acetal carbon.

Preparation and Conformational Study of 19β,28-Epoxy-18α-olean-5-ene Derivatives

2006 ◽  
Vol 71 (3) ◽  
pp. 387-410 ◽  
Author(s):  
Martin Dračínský ◽  
Václav Richtr ◽  
Václav Křeček ◽  
Jan Sejbal ◽  
Jiří Klinot ◽  
...  
Keyword(s):  
Double Bond ◽  
Coupling Constants ◽  
Conformational Study ◽  
Hydrogen Atoms ◽  
Vicinal Coupling Constants ◽  
Starting Compound ◽  
New Type ◽  
Type 3

New oleanane type triterpenoids with the 5(6) double bond were prepared using partial demethylation on carbon C-4. The starting compound was 23-hydroxybetulin (1b) and the key reaction was the methylation of 19β,28-epoxy-24-nor-18α-olean-4-en-3-one (3b). The 5(6) double bond was used in preparation of new derivatives with an epoxy or oxo substituent in ring B. The conformation of ring A of new type 3-oxo oleanane derivatives with a double bond or a substituent on ring B was elucidated from vicinal coupling constants of hydrogen atoms in positions 1 and 2.

Discussion on 13C nuclear magnetic resonance spectra of structurally rigid cyclonucleosides. Violation of Karplus relationship between 3JC,H and dihedral angles

1984 ◽  
Vol 62 (8) ◽  
pp. 1555-1557 ◽  
Author(s):  
Jun Uzawa ◽  
Kentaro Anzai
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Dihedral Angles ◽  
Vicinal Coupling Constants ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Karplus Relationship ◽  
Derivatives Of ◽  
C Nmr

Using structurally rigid cyclonucleoside derivatives of adenosine, the effect of the oxygen functional groups on the vicinal coupling constants between carbon and hydrogen in, 13C nmr was investigated.

Proton spin–spin coupling constants and intramolecular hydrogen bonding in bromine derivatives of 1,3-dihydroxybenzene

1976 ◽  
Vol 54 (14) ◽  
pp. 2228-2230 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The conformational preferences in CCl4 solution at 32 °C of the hydroxyl groups in bromine derivatives of 1,3-dihydroxybenzene are deduced from the long-range spin–spin coupling constants between hydroxyl protons and ring protons over five bonds. Two hydroxyl groups hydrogen bond to the same bromine substituent in 2-bromo-1,3-dihydroxybenzene but prefer to hydrogen bond to different bromine substituents when available, as in 2,4-dibromo-1,3-dihydroxybenzene. When the OH groups can each choose between two ortho bromine atoms, as in 2,4,6-tribromoresorcinol, they apparently do so in a very nearly statistical manner except that they avoid hydrogen bonding to the common bromine atom.

Formation of H -Addition Radicals in Adenine Derivatives

1976 ◽  
Vol 31 (5-6) ◽  
pp. 225-231 ◽  
Author(s):  
H. Zehner ◽  
W. Flossmann ◽  
E. Westhof
Keyword(s):  
Esr Spectroscopy ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
X Rays ◽  
Hydrogen Atoms ◽  
Indo Calculations ◽  
Differential Stability ◽  
Purine Ring ◽  
Bonding Scheme ◽  
Adenine Derivatives

The formation of H-aduition radicals in monocrystals of 9-methyl adenine, deoxyadenosine monohydrate, and adenosine hydrochloride by irradiation with X-rays has been studied using ESR spectroscopy. In 9-methyl adenine and adenosine-HCl, hydrogen atoms add exclusively to position C8 of the imidazole part of the purine ring. On the other hand, in deoxyadenosine · H2O crystals, H-addition radicals at position C2 of the pyrimidine part of the purine ring occur together with H-addition radicals at position C8. Both radicals could be isolated by using their differential stability under warming or illumination with light. The C8-addition radical is characterized by two equivalent β-protons of 38.0 ± 0.5 G and the C2-addition radical by two non-equivalent β-protons of 34.0 ±1.0 and 50.0 ± 1.0 G. The nitrogen splittings perpendicular to the purine ring are 27.0 and 6.6 G for the C2-addition radical and 20.5 and 9.2 G for the C2-addition radical. The coupling constants of both radicals are in agreement with INDO calculations. It is further shown that the added hydrogen atom comes partly from the hydrogen bonding scheme and partly from the non­exchangeable hydrogens for the C8-addition radical. Together with additional experiments on polycrystalline samples, these results lead to the conclusion that hydrogen atoms add non-selectively to C2 and C8 of the neutral molecules, whereas protons add predominantly to C8 of anion radicals. This is supported by Hückel molecular orbital calculations.

scholarly journals IDENTIFICATION AND SEQUENCING BY NMR SPECTROSCOPY OF THE CARBOHYDRATE MOIETY IN A SAPONIN FROM Barringtonia asiatica

2010 ◽  
Vol 1 (3) ◽  
pp. 120-124
Author(s):  
Rymond J Rumampuk
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Coupling Constants ◽  
Carbohydrate Moiety ◽  
Glycosidic Linkage ◽  
1H And 13C Nmr ◽  
Heteronuclear Correlation ◽  
Vicinal Coupling Constants ◽  
Nmr Signals

A trisaccharide chain in a saponin from the seeds of Barringtonia asiatica has been identified and sequenced as {[b-D-galactopyranosyl(1®3)- b-D-glucopyranosyl(1®2)]-b-D-glucuronopyranosyloxy} using a combination of homonuclear and heteronuclear correlation NMR spectroscopy. The 1H and 13C NMR signals of the sugar residues can be determined and distinguished from one other by use of the HMQC-TOCSY technique. Anomeric configurations were unambiguously assigned from the vicinal coupling constants 3JH-1,H-2 of the anomeric protons. Inter-glycosidic linkage assignments were elucidated using  HMBC.   Keyword: Barringtonia asiatica, carbohydrate, saponin, NMR

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