Advanced Topic 215 of 1102 Bonding & Molecular Structure
Banana Bonds
Bent bonds in strained molecules where overlap is off the internuclear line.
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In-depth explanation of Banana Bonds
Banana bonds, also called bent or tau bonds, are carbon-carbon bonds in strained rings in which the electron density lies off the line joining the two nuclei. Such bonds form when ideal sp3 orbital overlap is impossible because of small ring angles, so the orbitals overlap at an angle and the bond bends outward. The result is a bond with greater p character, higher energy and increased reactivity compared with an unstrained bond. Banana bonds help explain the ring-opening reactions of cyclopropane. The concept is used to understand strain energy in small rings.
Going deeper: Banana Bonds
Key ideas: Quantify with ring strain: cyclopropane has angle 60 versus 109.5, strain energy about 115 kJ/mol, and cyclobutane about 110 kJ/mol. The inter-orbital angle in cyclopropane is about 104 degrees rather than 60, so overlap lies off the internuclear axis. C-C bonds are 151 pm, shorter than normal, and have greater p character, while the C-H bonds have about sp2 character.
Common mistakes and connections: A typical mistake is believing the C-C bond is straight and just strained, or that cyclopropane is unreactive because it is saturated. It undergoes ring-opening with hydrogen and bromine, a bit like an alkene. Cyclohexane, in contrast, is nearly strain free in its chair form. Links to hybridization, strain energy, Bent's rule and reactivity of small rings.
Visualization of Banana Bonds
Ring strain is largest in cyclopropane, where 60 degree C-C-C angles force bent banana bonds, and vanishes in cyclohexane. The interactive lesson shows this as a live animation or chart.
Worked example and use case
In cyclopropane the C-C-C angle is 60 degrees rather than 109.5 degrees, which forces the bonds to bend.
Frequently asked questions about Banana Bonds
What is Banana Bonds?
Bent bonds in strained molecules where overlap is off the internuclear line.
Is Banana Bonds a beginner, intermediate or advanced topic?
Banana Bonds is a advanced topic in Bonding & Molecular Structure. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Banana Bonds?
Study these earlier topics in Bonding & Molecular Structure first: Hydrogen Molecule Ion, Hypervalency, Three-Center Two-Electron Bond.
What comes after Banana Bonds?
The next topics in Bonding & Molecular Structure are Van der Waals Radius and Covalent Radius.
Can I practise Banana Bonds with quizzes?
Yes. The interactive lesson includes a self-check question on Banana Bonds, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Banana Bonds fits in Bonding & Molecular Structure
Banana Bonds is topic 100 of 104 in Bonding & Molecular Structure.