Light has been used from ages to analyze and characterize the different properties of chemical compounds and more preferably for organic molecules made up of carbon and other elements such as hydrogen and oxygen. Light in short as electromagnetic radiation in form of plane polarized form is known to be visible for a human eye at a range of 380-400 nanometers and ranges to 760-780 nanometers.
The property of optical rotation in turn is associated as the property to turn the plane of polarized light along the direction of motion in which the light is expected to travel across various materials. The phenomenon of optical rotation or specific rotation is of wide application in the sugar industry as a method to determine the concentration of syrup and also helps in characterization of various substances.
Optical Rotation of Glucose
Glucose represents the simple monosaccharide representative of carbohydrates and is most studied molecule for the understanding of optical rotation. Various signs are in use to explain and understand the optical rotation.
(+) indicates that sample which is optically active rotates in clockwise direction
(-) indicates that sample which is optically active rotates in counterclockwise direction
(D) and L conformation are used from remote to represent the clockwise rotation referred as dextrorotation and in counterclockwise direction in turn referred as levorotation. The dextrorotatory indicates movement on right side where as levorotatory represents movement of left side
Off late the D and L conformation as terms is used to explain the chiral nature of specific carbon atom present in the carbohydrate. D-glyceraldehye molecule in dextrorotatory nature used as reference molecule to understand the polarization.
Apart from D and L conformation off late R and S are used to describe the Cahn-Ingold-Prelog rule which are portrayed to understand the arrangement of various substituents which are lined up to the chiral carbon and can range from H, OH, CHO, and CH2OH.
Mutarotation Associated with Glucose as Reference
It is well noted that carbohydrates are optically active and glucose molecule exists in 2 crystalline forms which are dextrorotatory in nature. The one peculiar form is known to melt at 1460C with specific optical rotation of +1120. The other characteristic form melts at 1500C with specific optical rotation of +18.70.
Once dissolved in water the form which melts at 1460C shows decrease in optical rotation from +1120 to +52.70 and in parallel the other form which melts at 1500C shows increase in optical rotation from +18.70 to +52.70. The variation in optical rotation in glucose molecule is referred as mutarotation.