Main Difference – D vs L Glucose
Isomerism is divided into two broad categories as structural isomerism and stereoisomerism. D and L isomers are stereoisomers that have the same chemical structure but are non-superimposable mirror images of each other. Glucose is a sugar molecule that is found as either D Glucose or L Glucose in nature. The main difference between D and L Glucose is that D Glucose rotates plane polarized light clockwise whereas L Glucose rotates plane polarized light anticlockwise.
What is D Glucose
D Glucose is a sugar molecule that can rotate the plane polarized light in the clockwise direction. In the Fischer projection, D Glucose shows four –OH groups on the sides of the main carbon chain. Three of the –OH groups are on the right side whereas other –OH group is on the left side (-OH group attached to the 3rd carbon atom).
In the Haworth projection of the D Glucose, one of the –OH groups is directed upward whereas other –OH groups are downward. D Glucose is the form of Glucose that is found abundant in nature. It is the basic form of energy storage and living beings use D Glucose to fulfil their energy needs.
What is L Glucose
L Glucose is the mirror image of D Glucose. But this mirror image is non-superimposable with D Glucose. Therefore, L Glucose is considered as the enantiomer of D Glucose. Since it is the mirror image, the –OH groups of the Fischer projection are located in completely opposite directions. This structure also has three –OH groups at the same side and other –OH group on the opposite side. But unlike in D Glucose, three –OH groups are on the left side of the main carbon chain whereas other –OH group is located on the right side.
In the Fischer projection of D Glucose, the –OH groups are located in the opposite directions compared to the Fischer projection of D Glucose. When considering the Haworth projection, the three –OH groups are directed upward and the –OH group attached to the 3rd carbon is directed downward. L Glucose is not abundant in nature. But L Glucose can be found in some fruits and vegetables. Since it is the non-superimposable mirror image of D Glucose, the molecular formula and the molar mass are the same for D and L Glucose isomers. But the chemical properties and their occurrence would be different due to different spatial arrangements.
