Glucose structure open chain.
The structure of glucose may be discussed under the following heads : (a) Open chain formula ; (b) Configuration ; (c) Cyclic structure ; (d) Haworth representation.
A. Open-chain Formula.
The open-chain formula of glucose is constructed from the following facts:
1. Molecular formula.
Elemental analysis and molecular weight determination have established that glucose has the molecular formula C6H12O6.
2. Presence of 6-carbon unbranched chain.
The complete reduction of glucose with concentrated hydrogen iodine and red phosphorus gives n-hexane. This proves that the glucose molecule is made of an unbranched six-carbon chain.
3. Presence of 5 OH groups.
Glucose reacts with acetic anhydride to form a pentadactyl derivative. This shows the presence of five hydroxyl groups. Since glucose is a stable compound, no two OH group are attached to the same carbon. In other words, the five OH groups are on different carbons.
4. Presence of C=O group.
Glucose reacts with hydroxylamine to form an oxime. It suggests the presence of a carbonyl group.
5. Presence of terminal CHO function.
On mild oxidation with bromine water, glucose is converted to gluconic acid which when reduced with an excess of Hl yields n-hexanoic acid.
This shows that glucose contains a six-carbon straight chain with CHO at one end, which has been oxidized to COOH.
6. Construction of open-chain formula.