The key difference between prototropy and tautomerism is that prototropy discusses two forms of a molecule that differ from each other only in the position of a particular proton whereas tautomerism discusses the interconversion of two structural isomers via relocation of atoms or bonds.
Prototropy is a form of tautomerism; it is the most common form of tautomerism. Tautomerism is a concept in organic chemistry that describes the conversion of one structural isomer into another isomer via relocation of atoms or bonds. If the relocation occurs in a proton in the molecule, then we call it prototropy. Therefore, this type of tautomerism is known as prototropic-tautomerism.
CONTENTS
1. Overview and Key Difference
2. What is Prototropy
3. What is Tautomerism
4. Side by Side Comparison – Prototropy vs Tautomerism in Tabular Form
5. Summary
What is Prototropy?
Prototropy is a type of tautomerism where the relocation of a proton occurs. It is the most common form of tautomerism. Therefore, it is also named as prototropic-tautomerism. We can consider it as a subset of acid-base behaviour. The prototropic tautomers are isomers that undergo isomeric protonation between molecules having the same empirical formula and total charge. Acids and bases can catalyze these reactions.
There are two types of prototropic-tautomerism; annular tautomerism and ring-chain tautomerism. In the annular tautomerism, a proton tends to occupy two or more positions of a heterocyclic system. In ring-chain tautomerism, the movement of the proton is accompanied by a change from an open structure to a ring structure.
What is Tautomerism?
Tautomerism is a concept in organic chemistry that describes the effect of having several compounds that are capable of interconversion via relocating an atom or a chemical bond. This type of interconversion is most common in amino acids and nucleic acids. The process of interconversion is known as tautomerization, which is a chemical reaction. In this interconversion process, the relocation of protons or chemical bonds means the exchange of a hydrogen atom between two other forms of atoms or the rapid formation or rupture of single or double bonds.
If tautomerization occurs with the relocation of a proton, then it is called prototropy. If tautomerization occurs with the relocation of a single or a double bond, then it is called valence tautomerism. The hydrogen atom forms a covalent bond with the new atom that receives the hydrogen atom. Tautomers exist in equilibrium with each other. They always exist in a mixture of two forms of the compound since they attempt to prepare the separate tautomeric form.
Figure 01: Valence Tautomerism
During the process of tautomerization, the carbon skeleton of a molecule does not change. Only the position of protons and electrons are changed. The process is an intramolecular chemical process of conversion of one form of tautomer into a different form. A common example is a keto-enol Tautomerism. It is an acid or base-catalyzed reaction. Typically, the keto form of an organic compound is more stable, but in some states, the enol form is more stable than the keto form.
What is the Difference Between Prototropy and Tautomerism?
Prototropy and tautomerism are closely related terms; prototropy is a type of tautomerism. The key difference between prototropy and tautomerism is that prototropy discusses two forms of a molecule that differs from each other only in the position of a particular proton whereas tautomerism discusses the interconversion of two structural isomers via relocation of atoms or bonds.
Below is a summary of the difference between prototropy and tautomerism in tabular form.
Summary – Prototropy vs Tautomerism
Prototropy and tautomerism are closely related terms; prototropy is a type of tautomerism. The key difference between prototropy and tautomerism is that prototropy discusses two forms of a molecule that differs from each other only in the position of a particular proton whereas tautomerism discusses the interconversion of two structural isomers via relocation of atoms or bonds.
Reference:
1. “Definitions for Prototropypro·Totropy. ” Definitions, Available here.
Image Courtesy:
1. “Oxepin-benzene oxide” By Edgar181 – Own work (Public Domain) via Commons Wikimedia