Related Experiment Video
Updated: Mar 29, 2026
07:56
Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyltroponeiron
Published on: August 12, 2019
8.4K
Why Cyclooctatetraene Is Highly Stabilized: The Importance of "Two-Way" (Double) Hyperconjugation
Judy I Wu1, Israel Fernández2, Yirong Mo3
1Department of Chemistry, University of Georgia , Athens, Georgia 30602, United States.
Journal of Chemical Theory and Computation
|November 25, 2015
Summary
Cyclooctatetraene (COT) is not a simple polyene; its nonplanar shape stabilizes it through "two-way" hyperconjugation. This electronic effect, involving sigma and pi orbitals, explains its unexpected stability.
Area of Science:
- Quantum Chemistry
- Organic Chemistry
- Computational Chemistry
Background:
- Cyclooctatetraene (COT) exhibits a nonplanar, tub-shaped D2d geometry.
- Despite its geometry, COT retains significant pi interactions, challenging the view of it as a purely unconjugated polyene.
Purpose of the Study:
- To investigate the electronic stabilization of the D2d cyclooctatetraene (COT) minimum.
- To elucidate the role of "two-way" hyperconjugation in compensating for lost pi conjugation.
Main Methods:
- Isodesmic bond separation energy (BSE) calculations were employed.
- Analysis of electronic interactions between sigma (σ/σ*) and pi (π/π*) orbitals.
Main Results:
- The D2d COT minimum shows substantial stabilization energy (41.1 kcal/mol) via BSE.
- This stabilization is primarily attributed to "two-way" hyperconjugation across C-C single bonds.
- This hyperconjugation compensates for the partial loss of pi conjugation due to ring puckering.
Conclusions:
- The tub-shaped D2d COT is electronically stabilized by "two-way" hyperconjugation.
- This mechanism is analogous to stabilization in 1,3-butadiene and other systems like allyl cation and biphenyl.
- Hyperconjugation plays a crucial role in the electronic structure of nonplanar conjugated systems.
More Related Videos
Related Concept Videos
01:18Aromatic Hydrocarbon Cations: Structural Overview
4.3K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
4.3K
02:30Stability of Substituted Cyclohexanes
17.3K
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
17.3K
02:02Chair Conformation of Cyclohexane
21.4K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
21.4K
02:11Conformations of Cyclohexane
17.3K
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
17.3K
02:29Conformations of Cycloalkanes
16.7K
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3 hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
16.7K
01:28Stability of Conjugated Dienes
4.7K
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
4.7K