fischer projection

• absolute configuration
  • 
  • The chiral carbon furthest from the carbonyl group determines the absolute configuration L or D of the sugar.
  • If in the fischer projection, the OH group on the chiral carbon furthest from the carbonyl is pointing left, then it's L. If it's pointing right, then it's D.
  • Note: L and D are enantiomers, not epimers. So, every chiral carbon center inverts. It's just that you assign L and D based on the chiral carbon furthest from the carbonyl.
• cyclic structure and conformations of hexoses
  • 
  • Fructose forms a furanose when carbon 5 attacks the carbonyl carbon.
  • 
  • Glucose forms a pyranose when carbon 5 attacks the carbonyl carbon.
  • Convert a Fischer projection to Haworth (cyclic) form
    • -OH groups that are pointing Left on the Fischer becomes Up on the Haworth.
    • -OH groups that are pointing Right on the Fischer becomes Down on the Haworth.
    • The -OH group on the anomeric carbon (the Fischer carbonyl) can be either up (beta) or down (alpha).
    • The CH₂OH group on the absolute configuration carbon (carbon 5) points up for D, and down for L.