The key difference between furanose and pyranose is that furanose compounds have a chemical structure that includes a five-membered ring system containing four carbon atoms and one oxygen atom whereas pyranose compounds have a chemical structure that includes a six-membered ring structure consisting of five carbon atoms and one oxygen atom.
Furanose and pyranose are collective terms that are used to name two different types of carbohydrates which are also saccharides. These are ring structures having carbon and oxygen atoms, so we can categorize them as heterocyclic structures.
CONTENTS
1. Overview and Key Difference
2. What is Furanose
3. What is Pyranose
4. Side by Side Comparison – Furanose vs Pyranose in Tabular Form
5. Summary
What is Furanose?
Furanose is a term used to name carbohydrates having a five-membered ring structure consisting of carbon and oxygen atoms. There is one oxygen atom in the ring along with four carbon atoms. The name “furanose” originates from the name “furan”, which is similar in structure due to the presence of oxygen heterocycle. However, unlike in furan, furanose compounds have no double bonds in the ring structure.
Figure 01: Structure of Beta-D-fructofuranose
We can identify the furanose ring structure as a cyclic hemiacetal of an aldopentose or a cyclic hemiketal of a ketohexose. The anomeric carbon atom of this ring structure is located at the right side of the oxygen atom. Generally, the highest-numbered chiral carbon atom is located at the left side of the oxygen atom in a Haworth projection, and this carbon atom determines whether the structure has a D-isomer or L-isomer of furanose or not. Typically, in the L-configuration of a furanose molecule, the substituent on the highest numbered chiral carbon is pointed downwards out of the plane while in the D-isomer the highest numbered chiral carbon faces the upward direction.
A furanose ring structure can occur in either the alpha configuration or in the beta configuration. This alpha or beta configuration of the furanose molecules is determined by the direction to which the anomeric hydroxy group is pointing. E.g. in D-furanose isomers, the hydroxy group is pointed downward in the alpha configuration. In the beta configuration, the hydroxy group is pointed in the upward direction.
What is Pyranose?
Pyranose is a term used to name carbohydrate molecules having the structure of a six-membered ring consisting of five carbon atoms along with one oxygen atom. However, there can be other carbon atoms that are located external to the ring structure.
Figure 02: Structure of Tetrahydropyran
The name “pyranose” originates from the name “pyran” due to its similarity in the ring structure. However, unlike in the pyran structure, there are no double bonds in the pyranose structure.
What is the Difference Between Furanose and Pyranose?
Furanose and pyranose are saccharide carbohydrate compounds. The key difference between furanose and pyranose is that furanose compounds have a chemical structure that includes a five-membered ring system containing four carbon atoms and one oxygen atom whereas pyranose compounds have a chemical structure that includes a six-membered ring structure consisting of five carbon atoms and one oxygen atom.
Moreover, furanose can be either a hemiacetal or a hemiketal, while pyranose has a hemiacetal structure.
Below infographic shows more comparisons related to the difference between furanose and pyranose.
Summary – Furanose vs Pyranose
Furanose and pyranose are saccharide carbohydrate compounds. The key difference between furanose and pyranose is that furanose compounds have a chemical structure that includes a five-membered ring system containing four carbon atoms and one oxygen atom whereas pyranose compounds have a chemical structure that includes a six-membered ring structure consisting of five carbon atoms and one oxygen atom.
Reference:
1. “Pyranose and Furanose Forms.” Libretexts. Retrieved October 09, 2020, Available here.
Image Courtesy:
1. “Beta-D-Fructofuranose” By NEUROtiker (talk · contribs) – Own work (Public Domain) via Commons Wikimedia
2. “TetrahydroPYRANE V.1” By Jü – Own work (CC0) via Commons Wikimedia