Difference Between Resonance and Tautomerism

Key Difference – Resonance vs Tautomerism
 

Isomerism is a chemical phenomenon that explains the structures of organic compounds having a same molecular formula with different structures and properties. Isomerism is the presence of different molecular structures and spatial arrangements of the same molecular formula. Isomers are categorized mainly into two groups as constitutional isomers and stereoisomers. Tautomers are a type of constitutional isomers. These are organic compounds that readily interconvert. Resonance, on the other hand, is phenomena of chemistry that describe the effect of lone pairs and bond electron pairs to the polarity of a compound. The key difference between resonance and tautomerism is that resonance occurs due to the interaction between lone electron pairs and bond electron pairs whereas tautomerism occurs due to the interconversion of organic compounds by relocating a proton.

CONTENTS

1. Overview and Key Difference
2. What is Resonance
3. What is Tautomerism
4. Side by Side Comparison – Resonance vs Tautomerism in Tabular Form
5. Summary

What is Resonance?

Resonance is a chemical concept that describes the interaction between lone electron pairs and bond electron pairs of a compound. This effect eventually determines the actual chemical structure of that organic or inorganic compound. The resonance effect can be observed in compounds having double bonds and lone electron pairs. The resonance results in polarity of molecules.

The resonance effect stabilizes a compound by delocalizing electrons in pi bonds. Electrons in molecules can move around atomic nuclei since an electron does not have a fixed position of atoms. Therefore, the lone electron pairs can move to pi bonds and vice versa. This happens in order to obtain a stable state. This electron movement process is known as resonance. The resonance structures can be used to obtain the most stable structure of a molecule.

A molecule can have several resonance structures based on the number of lone pairs and pi bonds present in that molecule. All the resonance structures of a molecule have the same number of electrons and the same arrangement of atoms. The actual structure of that molecule is a hybrid structure in all resonance structures. The resonance effect can be found in two types;

1. Positive resonance effect
2. Negative resonance effect

The positive resonance effect explains the resonance that can be found in compounds having a positive charge. Then the positive resonance effect helps to stabilize the positive charge in that molecule. Negative resonance effect explains the stabilization of a negative charge in a molecule. However, the hybrid structure that is obtained considering resonance has lower energy than all resonance structures.

What is Tautomerism?

Tautomerism is the effect of having several compounds that are capable of interconversion via relocating a proton. This effect is most common in amino acids and nucleic acids. The process of interconversion is known as tautomerization. It is a chemical reaction. Here, the relocation of protons means the exchange of a hydrogen atom between two other forms of atoms. The hydrogen atom forms a covalent bond with the new atom that receives the hydrogen atom. The 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.

During the tautomerization, carbon skeleton of a molecule does not change. Only the position of protons and electrons are changed. The tautomerization 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 Resonance and Tautomerism?

Summary – Resonance vs Tautomerism

Resonance and Tautomerism are important chemical concepts. Resonance is used to determine the actual structure of a chemical compound. Tautomerism determines the chemical structure of a compound, which is most stable at given conditions. There are many differences between two terms. The difference between resonance and tautomerism is that resonance occurs due to the interaction between lone electron pairs and bond electron pairs whereas tautomerism occurs due to the interconversion of organic compounds by relocating a proton.

Reference:

1.Brown, William H. “Tautomerism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 May 2014. Available here  
2.’Tautomerism’ , Department of Chemistry, University of Oxford. Available here 
3.“Resonance (Chemistry).” Wikipedia, Wikimedia Foundation, 16 Mar. 2018. Available here 

Image Courtesy:

1.’Phenol resonance’By Smallman12q – Own work, (Public Domain) via Commons Wikimedia 
2.’Acetylacetone keto-enol tautomerism’By Vaccinationist – Own work, (Public Domain) via Commons Wikimedia