THE ROLE OF LONE PAIR INTERACTIONS IN THE CHEMISTRY OF THE MONOSACCHARIDES - STEREO-ELECTRONIC EFFECTS IN UNSATURATED MONOSACCHARIDES

The X-ray crystallographic structural data for simple unsaturated monosaccharides do not support the participation of the electron density of a C2-C3 pi bond in the modification of the geometry at the anomeric center, or the existence of a vinylogous anomeric effect in glycals. The delocalization phenomena (n-sigma*, n-pi* and pi-sigma*) are insignificant in the ground states of the simple sugars, and n-n repulsions are the dominant stereo-electronic effects in these molecules.