The key difference between resonance and π conjugation is that resonance refers to the stability of a molecule in the presence of delocalized electrons, whereas π conjugation refers to the concept of pi electrons being distributed throughout the entire area of a molecule rather than belonging to a single atom in the molecule.
Resonance and π conjugation are closely related terms since π conjugation causes resonance in chemical compounds.
CONTENTS
1. Overview and Key Difference
2. What is Resonance
3. What is π Conjugation
4. Side by Side Comparison – Resonance vs π Conjugation 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. Generally, the effect of resonance is helpful in determining the actual chemical structure of that organic or inorganic compound. This effect also appears in chemical compounds containing double bonds and lone electron pairs. Moreover, this effect causes the polarity of molecules.
Resonance shows the stabilization of a chemical compound via delocalizing electrons in pi bonds. Here, electrons in molecules can move around atomic nuclei since an electron does not have a fixed position inside the atoms. Therefore, the lone electron pairs are able to move to pi bonds and vice versa. This happens in order to obtain a stable state. This electron movement process is known as resonance. Moreover, we can use resonance structures in order to obtain the most stable structure of a molecule.
Figure 01: Resonance in Benzonitrile
A molecule can have several resonance structures based on the number of lone pairs and pi bonds present in that molecule. All 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. There are two types of resonance effect: positive resonance effect and negative resonance effect.
The positive resonance effect explains the resonance that can be found in compounds having a positive charge. The positive resonance effect helps to stabilize the positive charge in that molecule. The 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 π Conjugation?
The term π conjugation refers to the delocalization in organic compounds where we can observe the distribution of nonbonding pi electrons through a molecule. Therefore, we can describe the electrons in a π conjugation system as the nonbonding electrons in that chemical compound. Moreover, this term refers to electrons that are not associated with a single atom or a covalent bond.
As a simple example, we can give benzene as an aromatic system having delocalized electrons. Generally, a benzene ring has six pi electrons in the benzene molecule; we often indicate these graphically using a circle. This circle means that pi electrons are associated with all the atoms in the molecule. This delocalization makes the benzene ring to have chemical bonds with similar bond lengths.
What is the Difference Between Resonance and π Conjugation?
Resonance and pi conjugation are closely related terms. The key difference between resonance and π conjugation is that resonance refers to the stability of a molecule in the presence of delocalized electrons whereas π conjugation refers to the concept of pi electrons being distributed throughout the entire area of a molecule rather than belonging to a single atom in the molecule.
The below infographic summarizes the difference between resonance and π conjugation in tabular form.
Summary – Resonance vs π Conjugation
Resonance and π conjugation are closely related terms where π conjugation causes the resonance in chemical compounds. The key difference between resonance and π conjugation is that resonance refers to the stability of a molecule in the presence of delocalized electrons whereas π conjugation refers to the concept of pi electrons being distributed throughout the entire area of a molecule rather than belonging to a single atom in the molecule.
Reference:
1. “Conjugation And Resonance In Organic Chemistry.” Master Organic Chemistry, 26 Jan. 2020, Available here.
Image Courtesy:
1. “Benzonitrile resonance” By Fung06831 – Own work (CC BY-SA 4.0) via Commons Wikimedia