Conformational Studies of D-Glycals by ¹H Nuclear Magnetic Resonance Spectroscopy

The Preferred Half-Chair Conformations of the Fully O-Acetylated D-Glycals (And Related Compounds), as Indicated by 1H N.m.r. Spectroscopy Show that the Coupling Constant 4J2,4 is the Most Sensitive to Conformational Change. All Six Fully O-Acetylated-D-Glycals Favour the 4H5(D) Conformation in Solution, Except Di-O-Acetyl-D-Xylal Which Adopts the Alternative 5H4(D) Conformation. These Conformational Preferences Can Be Rationalised by Considering the Interactions between the Substituants at C(3), C(4), and C(5) and the \u27 Allylic Effect \u27. with the Introduction of a Substituent at C(2) in Glucals and Galactals, Ring-Flattening or Inversion to the 5H 4 Conformation Can Take Place to Relieve Strain