The key difference between enantiotropic and monotropic is that enantiotropic refers to having different polymorphic states that are stable at different temperatures, whereas monotropic refers to having only one polymorph that is stable at all reasonable temperatures.
Enantiotropic and monotropic are terms that describe two different polymorphic systems. Polymorphism refers to the occurrence of several different forms of the same substance, having significant differences in their physical properties, such as the melting point, colour, hardness, density, electrical conductivity, heat of fusion, etc. There are two different categories that we can divide the polymorphic substance into. These categories are known as monotropic systems and enantiotropic systems.
CONTENTS
1. Overview and Key Difference
2. What is Enantiotropic
3. What is Monotropic
4. Similarities Between Enantiotropic and Monotropic
5. Side by Side Comparison – Enantiotropic vs Monotropic in Tabular Form
6. Summary
What is Enantiotropic
The term enantiotropic refers to a phenomenon where one polymorph is stable over one temperature range while another polymorph is stable over a different temperature range. Enantiotropic substances are polymorphic substances having two or more polymorphic states that have their stabilities at specific temperatures. In other words, one polymorphic state is stable at a certain temperature range while another polymorphic state of the same substance is stable at a different temperature range. Some examples of this type of enantiotropic substances include carbamazepine and acetazolamide.
What is Monotropic
The term monotropic refers to a phenomenon when a material exists in multiple forms, but only one it is stable at all temperatures and pressures. This term is useful in describing the polymorphism of substances.
Figure 01: The Structure of Metolazone
Monotropic systems are substances where only one polymorphic state is stable at all the temperature ranges. A good example of this type of substances is metolazone.
What is the Relationship Between Enantiotropic and Monotropic?
Polymorphism refers to the occurrence of several different forms of the same substance, having significant differences in their physical properties, such as the melting point, colour, hardness, density, electrical conductivity, the heat of fusion, etc. There are two different categories that we can divide the polymorphic substance into. These categories are known as monotropic systems and enantiotropic systems. Therefore, enantiotropic and monotropic are terms with opposing meanings.
What is the Difference Between Enantiotropic and Monotropic?
The terms enantiotropic and monotropic are opposite to each other. The term enantiotropic refers to a phenomenon where one polymorph is stable over one temperature range while another polymorph is stable over a different temperature range while the term monotropic refers to a phenomenon a material can exist in multiple forms, but only one of it is stable at all temperatures and pressures. The key difference between enantiotropic and monotropic is that the term enantiotropic refers to the state of having different polymorphic states that are stable at different temperatures, whereas the terms monotropic refers to the state of having only one polymorph that is stable at all the reasonable temperatures. Moreover, carbamazepine and acetazolamide are examples of enantiotropic substances whereas metolazone is an example of monotropic substances.
The following infographic summarizes the difference between enantiotropic and monotropic in tabular form.
Summary – Enantiotropic vs Monotropic
Enantiotropic and monotropic are different terms used in chemistry regarding the field of polymorphism. The key difference between enantiotropic and monotropic is that the term enantiotropic refers to the state of having different polymorphic states that are stable at different temperatures, whereas the terms monotropic refers to the state of having only one polymorph that is stable at all the reasonable temperatures.
Reference:
1. “Polymorphism- Types of Polymorphism: Relation between Polymorphs&Solvates.” Byjus, 14 Aug. 2020, Available here.
Image Courtesy:
1. “Metolazone” By Tomasz Dolinowski – Own work (CC0) via Commons Wikimedia