STEREOCHEMISTRY AT C-3 OF EVERNITROSE - FALLACY IN DETERMINATION OF STEREOCHEMISTRY AT QUATERNARY CENTERS USING NUCLEAR MAGNETIC-RESONANCE SPECTROSCOPY - X-RAY CRYSTAL-STRUCTURE OF METHYL 3-ACETAMIDO-2,3,6-TRIDEOXY-3-C,4-O-DIMETHYL-L-XYLO-HEXOPYRANOSIDE