What is the Difference Between Canonical Structure and Resonance Hybrid

The key difference between canonical structure and resonance hybrid is that canonical structure is less stable than resonance hybrid.

There is a difference between the stabilities of the canonical structure and the resonance hybrid of molecules because the resonance hybrid shows a negative charge due to equally shared electrons between oxygen atoms. The negative charge is then spread out over a large part of the molecule, which makes the molecule stable.

CONTENTS

1. Overview and Key Difference
2. What is Canonical Structure 
3. What is Resonance Hybrid
4. Canonical Structure vs Resonance Hybrid in Tabular Form
5. Summary – Canonical Structure vs Resonance Hybrid 

What is Canonical Structure?

A canonical structure can be described as a structure that can be used in solving unification problems that involve a projection applied to an unknown structure instance and a value. These are the resonance structures that can contribute to the true structure of a molecule upon bonding, which cannot be expressed via a single resonating structure. However, these structures have no real existence because they are used to represent resonance.

Generally, the scattering from canonical structures such as simple shapes, periodic structures, and man-made objects relies on the descriptive determination of the surface of these bodies. In simple geometric shapes, the evaluation can be performed analytically in a closed form involving geometric and electromagnetic parameters of the surface.

What is Resonance Hybrid?

Resonance hybrid can be described as a weighted average of all significant resonance contributors depicting the true electronic structure of a molecule. It is a molecular structure that is a combination of two structures having different pie-bond electron positions. The resonance hybrid represents the actual molecule as the average of the contributing structures.

For example, benzene is an aromatic hydrocarbon compound having the molecular formula C₆H₆. Generally, it contains a cyclic structure, and the molecules are arranged in such a way that it consists of alternating single and double bonds between carbon atoms. The benzene molecule has two probable benzene resonance configurations that can be shown by rotating the bonds and resonance hybrid, the structure that is equal to both structures that are possible. The resonance of benzene is due to the presence of pi bonds that take part in delocalization, and it gives the resonating structures. Moreover, the delocalizing can cause each carbon-carbon bond to consist of a bond order of 1.5. This implies that they are stronger than regular carbon-carbon sigma bonds.

What is the Difference Between Canonical Structure and Resonance Hybrid?

Canonical structure and resonance hybrid structure are two major molecular-electronic structures that we can draw for a particular molecule. The key difference between canonical structure and resonance hybrid is that canonical structure is less stable than resonance hybrid. This is because the electrons in the canonical structure are usually not evenly distributed throughout the molecule (exceptions occur), which makes the structure unstable. But for resonance hybrid, the electrons are spread through the structure evenly, which makes it very stable.

The below infographic presents the differences between canonical structure and resonance hybrid in tabular form for side-by-side comparison.

Summary – Canonical Structure vs Resonance Hybrid

The electrons in the canonical structure are usually not evenly distributed throughout the molecule, making the structure unstable. However, the electrons in a resonance hybrid are spread through the structure evenly, making it very stable. Therefore, the key difference between canonical structure and resonance hybrid is that canonical structure is less stable than resonance hybrid.

Reference:

1. “Canonical Structure.” An Overview | ScienceDirect Topics.

2. “What Is Resonance Frequency?” Physics Q&A – Byju’s.

Image Courtesy:

1. “Carboxylate-canonical-forms” By Hbf878 – Own work (CC0) via Commons Wikimedia
2. “Nitrite-ion-resonance-hybrid” By Hbf878 – Own work (CC0) via Commons Wikimedia