The difference between structural and optical isomers in carbohydrates is that structural isomers are different structures of the same chemical formula, whereas optical isomers are different mirror images of the same structure.
Structural isomers and optical isomers are common in organic compounds such as carbohydrates. The basis for the designation of the isomers of all carbohydrates is glyceraldehyde. It is the simplest carbohydrate which has optical isomerism.
CONTENTS
1. Overview and Key Difference
2. What are Structural Isomers in Carbohydrates
3. What are Optical Isomers in Carbohydrates
4. Side by Side Comparison – Structural vs Optical Isomers in Carbohydrates in Tabular Form
5. Summary
What are Structural Isomers in Carbohydrates?
Structural isomers of carbohydrates are the different structural forms of the same chemical formula. The chemical formula of a compound gives the chemical elements present in the compound and the number of atoms per each chemical element. However, it does not give details about the structure. Therefore, there can be different structures for the same chemical formula; for example, glucose and fructose are structural isomers of each other. Moreover, both these compounds have the same chemical formula C6H12O6. But they have different structures, which leads to glucose having an aldehyde functional group and fructose a ketone functional group.
Figure 01: Structure of D-fructose and D-Glucose
What are Optical Isomers in Carbohydrates?
Optical isomers in carbohydrates are the different mirror images of the same structure. Therefore, these structures are identical in every way except that they are mirror images of each other. We name them as D and L isomers.
Figure 02: Alpha and Beta Glucose Molecules
If we take glyceraldehyde as an example, in the D isomer, the –OH group of glyceraldehyde projects to the right side while in L isomer, it is in the left side. Usually, naturally occurring monosaccharides are D isomers. Another common example of optical isomers is alpha and beta glucose.
What is the Difference Between Structural and Optical Isomers in Carbohydrates?
Carbohydrates show structural isomerism as well as optical isomerism. The key difference between structural and optical isomers in carbohydrates is that the structural isomers are different structures of the same chemical formula, whereas optical isomers are different mirror images of the same structure. Therefore, structural isomers have different functional groups, but optical isomers have the same functional group.
Summary – Structural vs Optical Isomers in Carbohydrates
In summary, the carbohydrates show isomerism, and structural isomers and optical isomers are two isomers. Here, the key difference between structural and optical isomers in carbohydrates is that the structural isomers are different structures of the same chemical formula, whereas optical isomers are different mirror images of the same structure.
Reference:
1. “4.1 Senior Biology 1, The Chemistry of Life: Carbohydrates TEST.” Quizlet, Available here.
Image Courtesy:
1. “D-Fructose vs. D-Glucose Structural Formulae V.1” By Jü – Own work (CC0) via Commons Wikimedia
2. “BB05_alpha beta glucose” By fickleandfreckled (CC BY 2.0) via Flickr