The key difference between backbonding hyperconjugation and conjugation is their bond formation. Backbonding is the movement of electrons from an atomic orbital on one atom to an antibonding pi orbital on a ligand while hyperconjugation is the interaction of sigma bonds with a pi network, and conjugation is the overlap of pi orbitals along a sigma bond.
We can discuss the terms backbonding, hyperconjugation and conjugation with reference to the different chemical bonding in compounds. All three terms describe the overlapping of electron orbitals other than the major covalent bonds in the molecule.
CONTENTS
1. Overview and Key Difference
2. What is Hyperconjugation
3. What is Backbonding
4. What is Conjugation
5. Side by Side Comparison – Backbonding Hyperconjugation vs Conjugation in Tabular Form
6. Summary
What is Backbonding
Backbonding refers to the movement of electrons from an atomic orbital on one atom to an antibonding pi orbital on a ligand. Here, the antibonding orbital and the atomic orbital should have the appropriate symmetry in order to overlap perfectly. This type of chemical bonding is common in organometallic chemistry of transition metals containing multiatomic ligands such as carbon monoxide, ethylene, etc.
Figure 01: Backbonding
What is Hyperconjugation?
The term hyperconjugation refers to the interaction of σ-bonds with a pi network. In this interaction, electrons in a sigma bond interact with an adjacent partially (or completely) filled p orbital, or with a pi orbital. This type of interactions takes place to increase the stability of a molecule.
Figure 02: Hyperconjugation
Generally, hyperconjugation happens because of the overlap of bonding electrons in C-H sigma bond with a p orbital or a pi orbital of the adjacent carbon atom. Here, the hydrogen atom resides in close proximity as a proton. The negative charge that develops on the carbon atom is delocalized due to the overlap of p orbital or pi orbital.
What is Conjugation?
The term conjugation describes the overlap of p-orbitals across a σ bond (sigma bond). In chemistry, a sigma bond is a type of a covalent bond. Usually, unsaturated compounds having double bonds are composed of one sigma bond and a pi bond. The carbon atoms of these compounds undergo sp2 hybridization before forming the bond. Then, there is an unhybridized p orbital per each carbon atom.
Figure 03: Alternating Pi System
If there is a compound having alternating single bonds (sigma bonds) and double bonds (a sigma bond and a pi bond), the unhybridized p orbitals can get overlapped with each other, forming an electron cloud. Then, the electrons in those p orbitals get delocalized inside this electron cloud. This kind of delocalized system is known as a conjugated system, and we can name this overlapping of p orbitals as conjugation.
What is the Difference Between Backbonding Hyperconjugation and Conjugation?
We can discuss the terms backbonding, hyperconjugation and conjugation with reference to the different chemical bonding in compounds. Backbonding is the movement of electrons from an atomic orbital on one atom to an antibonding pi orbital on a ligand and hyperconjugation is the interaction of sigma binds with a pi network whereas conjugation is the overlap of pi orbitals along a sigma bond. So, this is the key difference between backbonding hyperconjugation and conjugation.
Below infographic tabulates more differences between backbonding hyperconjugation and conjugation.
Summary – Backbonding Hyperconjugation vs Conjugation
The key difference between backbonding hyperconjugation and conjugation is that backbonding is the movement of electrons from an atomic orbital on one atom to an antibonding pi orbital on a ligand and hyperconjugation refers to the interaction of sigma binds with a pi network whereas conjugation refers to the overlap of pi orbitals along a sigma bond.
Reference:
1. “Pi Backbonding.” Wikipedia, Wikimedia Foundation, 5 July 2020, Available here.
Image Courtesy:
1. “Back bonding” By OMCV – Own work (Public Domain) via Commons Wikimedia
2. “Alkene-hyperconjugation2” By Alsosaid1987 – Own work (CC BY-SA 4.0) via Commons Wikimedia
3. “Beta-Carotene conjugation” By Rubber Duck (☮ • ✍) – Own work (Public Domain) via Commons Wikimedia
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