Chemistry Biomolecules: Overview, Questions, Preparation

Above are the acyclic and cyclic structures of glucose, respectively. 

Glucose is correctly named D(+) Glucose, wherein D represents the configuration, and + indicates the molecule’s dextrorotatory nature.  

Baeyer introduced the acyclic or the open chain structure of glucose. However, this structure could not explain certain properties, like no reaction to Schiff’s test or with hydroxylamine or sodium hydrogen sulphite, or even the process of mutarotation.

The cyclic structure of glucose was introduced by Haworth, which confirmed mutarotation and the existence of alpha and beta forms of glucose. The ring structure has no free aldehyde group. The cyclic structure has one chiral centre more than the acyclic form. Therefore, two isomeric forms are possible, which differ in the configuration of the hydroxyl group at C1.

The six-membered ring structures of glucose are called pyranose structures, and hence the isomers are alpha D + and beta D + glucopyranose.

Fructose is an important ketohexose, obtained along with glucose during the hydrolysis of disaccharides like sucrose. The pure form of fructose is used as a sweetener and is commonly found in fruits, vegetables, and honey. Discovered in 1847 by French chemist Augustin-Pierre Dubrunfaut, it consists of a 6-carbon polyhydroxy ketone.

Fructose has the molecular formula C6H12O6 an, and it contains a ketonic group at C2. It belongs to the D series and is a levorotatory compound written as D-(-) fructose. It’s open, and cyclic is as shown in the above image, respectively.

It exists in 2 cyclic forms by the addition of -OH group at C5, resulting in a five-membered ring that has the analogy of Furan. Its two isomers are named alpha D-(-) fructofuranose and beta D-(-) fructofuranose.