What is the Difference Between Furanose and Pyranose?

Furanose and pyranose are collective terms used to name two different types of ring structures found in carbohydrate compounds. The key difference between them lies in the number of members in their respective ring structures:

• Furanose: These compounds have a five-membered ring structure, consisting of carbon and oxygen atoms, forming a heterocyclic structure. Furanose can be either a hemiacetal or a hemiketal.
• Pyranose: These compounds have a six-membered ring structure, also consisting of carbon and oxygen atoms, forming a heterocyclic structure. Pyranose has a hemiacetal structure.

Both furanose and pyranose forms are common in sugars, and their stability can vary depending on the specific sugar and its environment. For example, the pyranose form of glucose is more stable than its furanose form due to the 60° dihedral angle between the C5-OH and the C4-C3 bond in the pyranose structure. However, for fructose, the furanose form is more prevalent, as the energy required to distort the bond angles in a six-membered pyranose ring would be too high.

Comparative Table: Furanose vs Pyranose

Furanose and pyranose are cyclic forms of sugars that result from the reaction of a hydroxyl group with the carbonyl group in the sugar molecule. The main differences between furanose and pyranose are the size of the cyclic ring and the hydroxyl group involved in the reaction. Here are the key differences between furanose and pyranose:

Both furanose and pyranose forms are part of the ring-chain tautomerism in sugars, where sugars exist in equilibrium between their open-chain form and various cyclic forms. The equilibrium tends to favor the six-membered cyclic form (pyranose) since it resembles pyran, although some of the five-membered cyclic form (furanose) is also present along with the open-chain form.