Structure of glucose
Glucose is a carbohydrate compound consisting of six carbon atoms and an aldehyde group and they are referred to as aldohexose. The glucose structure can exist in an open-chain (acyclic) and ring (cyclic) form.
Its chemical formula is C6H12O6, and this empirical formula is shared by other sugars - called hexoses - 6 carbon sugars.
In the open chain form an intramolecular reaction between the aldehyde C atom and the C-5 hydroxyl group forms an intramolecular hemiacetal. An equilibrium state is found in both the forms in water solution. Cyclic form of glucose contains 5 carbon and one oxygen atoms, which resembles to form the structure of pyran, it is also referred to as glucopyranose. The pyran ring has carbon linked to a hydroxyl side group. The fifth carbon atom is linked to a sixth carbon atom outside the ring, forming a CH2OH group.
The usual form of glucose found in nature is dextrarotatory, while the usual form of fructose is levorotatory. For those sugars having two or more asymmetric carbon atoms, the convention has been adopted that the prefixes D- and L- refer to the asymmetric carbon atom farthest removed from the carbonyl carbon atom.
Any two sugars differs in its configuration around one specific carbon atom are called epimers of each other. Thus, D-Glucose and D-mannose are epimers with respect to carbon atom 2, and D-glucose and D-galactose are epimers with respect to carbon atom 4.
Glucose is also called blood sugar and dextrose as it is being circulated in the blood at a concentration of 65-110 mg/mL of blood. In plants it is synthesized by the chlorophyll using carbon dioxide from the air and sunlight as an energy source, glucose is further converted to starch for storage.