1.10 Cyclic Forms of Monosaccharides

• Monosaccharides in nature have cyclic forms because they can form internal hemiacetals that are stable.
• Cyclic Hemiacetal Forms of D-Glucose

  
• 2 forms of D-Glucose:

  • α-form
  • β-form
• D-glucose form

  • the –OH of C1 and CH2OH of C5 are on opposite sides

  A) a-form

  
• D-glucose form

  • the –OH of C1 and CH2OH of C5 are on the same side

  A) B-form

  
• Anomeric carbon atom

  • the hemiacetal carbon atom present in a cyclic monosaccharide structure. It is the carbon atom that is bonded to an -OH group and to the oxygen atom in the heterocyclic ring.

  
• Anomers

  • cyclic monosaccharides that differ only in the positions of the substituents on the anomeric (hemiacetal) carbon atom. 
• Cyclic monosaccharide containing a six-atom ring 

  A) Pyranose

  
• • Cyclic monosaccharide containing a five-atom ring 

  A) Furanose