The key difference between delocalization and resonance is that delocalization refers to electrons being distributed throughout the entire area of a molecule rather than attached to a single molecule whereas resonance refers to the stabilization of a molecule due to delocalization of electrons.
Delocalization and resonance are related chemical concepts; the resonance effect is explained using the electron delocalization of chemical compounds.
CONTENTS
1. Overview and Key Difference
2. What is Delocalization
3. What is Resonance
4. Side by Side Comparison – Delocalization vs Resonance in Tabular Form
5. Summary
What is Delocalization?
Delocalization is a term that refers to the distribution of nonbonding pi electrons through a molecule. Therefore, we can describe delocalized electrons as the nonbonding electrons in that chemical compound. The term delocalization refers to electrons that are not associated with a single atom or a covalent bond. Nevertheless, the term delocalized electron has different meanings in different fields. For example, in organic chemistry, delocalized electrons are in the resonance structures of conjugated systems in aromatic compounds. Similarly, in solid-state physics, delocalized electrons are the free electrons that facilitate electrical conduction. Furthermore, quantum physics use the term delocalized electrons to refer to molecular orbital electrons that have extended over several atoms.
Figure 01: Electron Delocalization in Molecules
The simplest example that we can give for an aromatic system having delocalized electrons is the benzene ring. The 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 Resonance?
Resonance is a concept in chemistry that describes the interaction between lone electron pairs and bond electron pairs of a compound. The resonance effect helps to determine the actual chemical structure of that organic or inorganic compound. This effect appears in compounds having double bonds and lone electron pairs. Furthermore, this effect causes the polarity of molecules.
Figure 02: Resonance Structures of Butadiene
The resonance effect shows the stabilization of a chemical compound via delocalizing electrons in pi bonds. Generally, the 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.
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. 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. 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 the Difference Between Delocalization and Resonance?
Delocalization and resonance are two related chemical concepts. The key difference between delocalization and resonance is that delocalization refers to electrons being distributed throughout the entire area of a molecule rather than attached to a single molecule whereas resonance refers to the stabilization of a molecule due to delocalization of electrons.
Moreover, delocalization occurs in molecules having alternative single bonds and double bonds or triple bonds while resonance occurs in conjugated systems, or molecules having movable electrical charges.
Below infographic summarizes the differences between delocalization and resonance.
Summary – Delocalization vs Resonance
Delocalization and resonance are related chemical concepts; the resonance effect is explained using the electron delocalization of chemical compounds. The key difference between delocalization and resonance is that delocalization refers to the electrons being distributed throughout the entire area of a molecule rather than attached to a single molecule whereas resonance refers to the stabilization of a molecule due to delocalization of electrons.
Reference:
1. “Delocalization of Electrons.” Libretexts. Available here.
Image Courtesy:
1. “Delocalization-updated” By Alsosaid1987 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Butadiene-resonance” By Alsosaid1987 – Own work (CC BY-SA 4.0) via Commons Wikimedia