Relation entre conformation et résonance quadripolaire nucléaire du chlore: structure de deux dérivés chlorés de sucres de configuration manno

Abstract

(Recu le 10 avril 1975(Recu le 10 avril , acceptk le 2 juin 1975 Nuclear pure quadrupole resonance (n.q.r.) of the chlorine atom bound to carbon atom C(1) has been detected in several hexo-and pento-pyranosyl derivatives. Observed resonance frequencies are distributed over two groups centred respectively at 32.53 and 35"12 MHz. The structures of the two compounds which have the lower and higher frequency in the first group have been determined. The compounds are: tri-O-acetyl-6-deoxy-0c-e-mannopyranosyl chloride, C,207H17C1, (33"10 MHz) and tetra-O-acetyl-~-D-mannopyranosyl chloride, Cz409H19Cl, (31.57 MHz). 1017 X-ray reflexions for the first compound and 1638 for the second were collected on an automatic counter diffractometer (Cu Ks radiation). A multisolution tangent refinement procedure was used for solving the structures. Values of R are respectively 4"5 and 7.5 %. The two compounds crystallize in space group P212a2~, Z=4. The lattice parameters are respectively: a=8.653(3), b=24.992(6), c=7.261(3) A and a=10.744(3), b= 22.264(7), e = 7"833(3) A. The first compound adopts in the solid state the 1 C (L) conformation and the second the C 1 (D) conformation. In each case the C(1)-CI bond is axial. According to the particularly low value of the n.q.r, frequency, the C(1)-CI bond is significantly lengthened in the second compound, 1.856(8) ~, compared with the value of 1.82 ~ found in hexo-and pento-pyranosyl chlorides. The implications of this on the properties of the axial C-CI bond are discussed.

Conformation de thio-sucres acycliques. IV. Structures du désoxy-1 éthylthio-1 (fluoro-5 uracil-1-yl)-1 D-arabinose aldéhydrol et de son homologue tétraacétylé

“…Cette disposition spatiale se retrouve ~galement darts les sucres cycliques ac6tyl+s (Cornfield, Mokren, Durette & Horton, 1972;Herpin, Famery, Auge & David, 1976). Une 6tude de sucre benzoyl6 (Luger, Durette & Paulsen, 1974) montre que le remplacement du groupe m6thyle par un ph6nyle semble ne pas modifier cette r+gle.…”