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Conformations of Cycloalkanes

Conformations of Cycloalkanes

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...

Conformations of Cyclohexane

Conformations of Cyclohexane

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...

Structure of Benzene: Kekulé Model

Structure of Benzene: Kekulé Model

In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.

Chair Conformation of Cyclohexane

Chair Conformation of Cyclohexane

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...

Structure of Conjugated Dienes

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...

Stability of Conjugated Dienes

Stability of Conjugated Dienes

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.

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Related Experiment Video

Updated: Feb 21, 2026

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Published on: September 18, 2016

Why Do Cumulene Ketones Kink?

Frank Weinhold¹

¹Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.

The Journal of Organic Chemistry

|October 10, 2017

Summary

This summary is machine-generated.

We investigated the electronic origins of "kinked" structures in cumulene ketones. Symmetry-breaking interactions explain these geometries and their sensitivity to external factors.

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Area of Science:

Computational chemistry
Quantum chemistry
Molecular structure

Background:

Extended cumulene ketones and diketones exhibit unusual
kinked
spine geometries.

Purpose of the Study:

To elucidate the electronic origin of these kinked geometries in cumulene monoketones and diketones.
To rationalize observed patterns in kinking behavior.

Main Methods:

Ab initio calculations
Density functional theory (DFT)
Natural Bond Orbital (NBO) analysis
Natural Resonance Theory (NRT)

Main Results:

Identified symmetry-breaking n_O^(π)-σ*_CC interactions as the dominant factor in kinking.
Demonstrated a link between kinking and carbon monoxide (CO) extrusion reactions.
Explained even/odd alternation in kinking, preference for trans-like kinks, and sensitivity to perturbations.

Conclusions:

The electronic structure, specifically lone pair-antibonding orbital interactions, dictates the kinking in cumulene ketones.
These findings provide a fundamental understanding of the stability and reactivity of these molecules.