The key difference between carbonium ion and carbanion is that carbon atom in carbonium ion is pentavalent while in carbanion it is trivalent.
Carbonium ion and carbanion are ionic forms of organic compounds which has charged carbon atoms. However, the two ions differ from each other according to the charge, valency of the carbon atom, chemical bonds, etc.
CONTENTS
1. Overview and Key Difference
2. What is Carbonium Ion
3. What is Carbanion
4. Side by Side Comparison – Carbonium Ion vs Carbanion in Tabular Form
5. Summary
What is Carbonium Ion?
Carbonium ion is a cation having a pentavalent carbon atom. The charge of the ion is +1, and the combination of carbon and hydrogen atoms in the compound can vary. For example, the simplest carbonium ion is methanium ion(CH5+), which has a carbon atom with +1 charge and five hydrogen atoms. Moreover, the carbon atom gets a +1 charge because there are five C-H bonds.
Figure 01: The Simplest Caronium Ion – Methonium Ion
The carbonium ion has planar geometry. We can obtain these ions by treating alkanes with very strong acids. However, in the industrial scale, the carbonium ions are formed during the refining of petroleum in the primary thermal cracking step.
What is Carbanion?
Carbanion is an anion having a trivalent carbon atom. The charge of this ion is -1. It has a carbon atom having three covalent bonds around it. Sometimes, there is no charge on the chemical species, but there is a negative charge in at least one of its resonance structures. We categorize such a chemical species as a carbanion.
Figure 2: Carbanions
Furthermore, the geometry of these anions can be trigonal pyramidal, bent or linear, depending on the substituent groups around the carbon atom. Typically, carbanions are basic and nucleophilic.
What is the Difference Between Carbonium Ion and Carbanion?
The key difference between carbonium ion and carbanion is that the carbon atom in carbonium ion is pentavalent while in carbanion it is trivalent. Moreover, a further difference between carbonium ion and carbanion is their geometry. The geometry around this caron atom in carbonium ion is planar. But, in carbanion, the geometry can be trigonal pyramidal, bent or linear depending on the substituents.
Furthermore, the charge of carbonium ion is +1 while in carbanion it is -1. Also, there are five covalent bonds around carbon atom in carbonium ion while in carbanion there are three covalent bonds.
Summary – Carbonium Ion vs Carbanion
Overall, carbonium ion and carbanion are charged chemical species containing carbon atoms with different valencies. The key difference between carbonium ion and carbanion is that the carbon atom in carbonium ion is pentavalent while in carbanion it is trivalent.
Reference:
1. Closs, Gerhard L. “Carbanion.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.
Image Courtesy:
1. “Methonium” By Matthias M. – Own work (Public Domain) via Commons Wikimedia
2. “Carbanion Structural Formulae V.1” By Jü – Own work (CC0) via Commons Wikimedia