Name: cyclohexane ring flip and axial bonds
Uploaded: 2023-04-30T18:28:33.000Z
Duration: 2 min 2 s
Channel: JoVE

The chair conformation, being the most stable and predominant form of cyclohexane, is non-planar, with the &#8220;headrest&#8221; and &#8220;footrest&#8221; bonds lying above and below the planar &#8220;seat&#8221; bonds.
The stability is a consequence of no angle strain &#8212; owing to the &#8216;almost tetrahedral&#8217; C-C-C bond angles &#8212; and no torsional strain &#8212; due to the perfectly staggered bonds.
The staggered arrangement is achieved when the substituents on each carbon arrange in two distinct orientations: axial and equatorial.
Axial bonds point straight up or straight down, parallel to the vertical axis of the ring.
Among the six axial bonds, three bonds are directed upward, while the remaining three bonds are directed downward, and the direction alternates from one ring carbon to the next.
The equatorial bonds point out sideways &#8212;&#160; positioned roughly along the equator of the ring &#8212; and are almost perpendicular to the vertical ring axis.
Out of the six equatorial bonds, three bonds have a slight upward slant, whereas the remaining three bonds have a slight downward slant.
Each carbon atom in the cyclohexane ring has an axial and an equatorial bond, pointing in opposite directions.
Moreover, each face of the ring has an alt

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&#8217;s bond angle being very close to the ideal tetrahedral bond angle of 109.5&#176; 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 staggered form. The axial bonds are directed straight up or down, lying parallel to the ring axis, whereas the equatorial bonds are pointed sideways roughly along the equator of the ring. Out of the six axial bonds, three are pointed up, and the remaining three are pointed downward. Similarly, three bonds are slanted upwards among the six equatorial bonds, while the remaining three are slanted downwards. Thus, each carbon atom in the cyclohexane ring has an axial and an equatorial bond, pointing in opposite directions.
A chair conformation of cyclohexane can undergo a conformational change into another chair conformer by the partial rotation of C-C bonds. This chair-chair interconversion that leads to the generation of two equivalent energy forms is known as ring flipping. Upon ring flipping, the axial and equatorial bonds interchange their positions. The axial bonds in one chair conformation get converted to equatorial bonds in the other chair conformation, while equatorial bonds change their position to axial bonds.

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 ...

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JoVE Core

Organic Chemistry

Unit 1

Alkanes and Cycloalkanes

KEY TERMS AND CONCEPTS

cyclohexane ring flip and axial bonds

Cyclohexane is most stable in the chair conformation. In this shape, the ring avoids angle strain because its bond angles are close to the ideal tetrahedral angle of 109.5°. It also avoids torsional strain because the bonds are arranged in a perfectly staggered way.

In the chair form, the hydrogen atoms attached to cyclohexane carbons take two positions: axial and equatorial. Axial bonds point straight up or down and run parallel to the ring axis. Equatorial bonds point outward, roughly along the ring’s equator.

The six axial bonds are split evenly, with three pointing up and three pointing down. The six equatorial bonds are also split, with three slanting up and three slanting down. As a result, each carbon in the ring has one axial bond and one equatorial bond that point in opposite directions.

Cyclohexane can change from one chair form to another by partial rotation of its C-C bonds. This chair-chair interconversion is called ring flipping. During a ring flip, axial and equatorial positions swap, so axial bonds in one chair become equatorial bonds in the other, and equatorial bonds become axial.

Cyclohexane Ring Flip and Axial Bonds

structure of alkanes

Alkane Bonding and Formula Patterns

Alkanes are the simplest hydrocarbons, and their structure starts with carbon-carbon bond formation. That idea helped shape organic chemistry, as August Kekulé and Archibald Scott Couper independently proposed carbon chain formation. Hydrocarbons are organic compounds made only of carbon and hydrogen. Based on the bond order between carbon atoms, hydrocarbons are classified as alkanes, alkenes, and alkynes. Alkanes contain sp3 hybrid carbon atoms. These carbons form sigma bonds with other sp3...

constitutional isomers of alkanes

Alkane Branching and Isomer Counts

Alkanes can form constitutional isomers, which are compounds with the same molecular formula but different structural formulas. This idea is called constitutional isomerism. It becomes important for alkanes with four or more carbons, because they can have more than one structure with the same formula. A straight-chain alkane is named with the prefix n, so the linear form of pentane is n-pentane. Branched isomers use prefixes such as iso and neo. Pentane has two branched isomers, iso-pentane...

nomenclature of alkanes

Naming Alkane Chains and Substituents

Alkane names follow IUPAC rules, a system used to name organic compounds in a clear and standard way. These rules became important in the late 19th century as new chemical compounds were discovered at a fast pace. IUPAC, the International Union for Pure and Applied Chemistry, was established in 1919 to set these naming rules. The naming process for alkanes depends on the length of the carbon chain, the number of substituents, and where those substituents are placed. The first step is to find...

physical properties of alkanes

How Alkane Chain Length Changes Properties

Alkane properties change with chain length and molecular shape. Alkanes contain only carbon and hydrogen, so they are nonpolar molecules. The electronegativity difference between carbon and hydrogen is very small, and alkanes therefore have a zero dipole moment. As a result, the only forces between alkane molecules are dispersion forces. Dispersion forces depend on surface area. In straight-chain alkanes, surface area increases as the carbon chain gets longer. That means dispersion forces also...

newman projections

Molecule Rotations in Newman Projections

Newman projections show molecule rotations around a single bond in a clear two-dimensional view. Chemists use several notations to show the three-dimensional shape of a molecule on a flat surface. The dash-wedge formula is one common way to do this. In that notation, dashed wedges show groups behind the plane, solid wedges show groups coming out of the plane, and plain lines show groups in the plane. Organic molecules can rotate around single bonds. This rotation creates many temporary...

conformations of ethane and propane

Ethane Rotation: Staggered vs Eclipsed

Ethane and propane show how rotation around a carbon-carbon single bond changes a molecule’s shape and energy. This internal rotation creates conformers, which are different arrangements of the same molecule. For ethane, the main conformations are staggered and eclipsed. Staggered ethane is the lower-energy, more stable form. In this shape, the C-H bonds on the front carbon sit 60° away from the C-H bonds on the back carbon. This spacing reduces torsional strain, which is the repulsion that...

conformations of butane

Butane’s Anti, Gauche, and Eclipsed Forms

Butane has several conformations, or shapes made by rotation around a carbon-carbon bond. Unlike ethane and propane, which have only two major conformations, butane shows more than two conformers. The lowest-energy form is the staggered anti conformer. In this shape, the two bulky methyl groups sit opposite each other at a dihedral angle of 180°. This spacing reduces steric repulsion, so the anti form is the most stable. Butane also has two other staggered conformations. These are degenerate,...

cycloalkanes

Cycloalkane Rings and Naming Rules

Cycloalkanes are saturated hydrocarbons with carbon atoms arranged in rings. Because they have two fewer hydrogen atoms than the matching open-chain alkane, their general formula is CnH2n. These ring structures are a common topic in organic chemistry. Chemists often draw cycloalkanes with line-angle formulas. In this shortcut, regular polygons stand for the ring, and each side shows a carbon-carbon bond. The number of corners in the polygon matches the number of carbons in the ring. Naming...

conformations of cycloalkanes

Cycloalkane Ring Strain and Shapes

Cycloalkane ring strain depends on ring shape, bond angles, and bond rotation. Adolf von Baeyer first tried to explain the stability of cycloalkanes with angle strain, which is the strain caused when bond angles differ from the ideal 109.5° tetrahedral angle for sp3-hybridized carbons. His idea worked well for some small rings, but not for every cycloalkane. Cyclopropane and cyclobutane are strained, as expected from their compressed bond angles. Cyclopentane is more strained than Baeyer...

conformations of cyclohexane

Cyclohexane Chair, Boat, and Twist-Boat Forms

Cyclohexane adopts non-planar shapes because a flat ring would create high angle strain and torsional strain. The molecule instead bends into chair and boat conformations. These shapes lower the strain and make the ring more stable. The chair conformation is the most stable form. It is named for its easy-chair shape. In this form, two carbon atoms sit out of the plane, with one above and one below. This arrangement minimizes torsional strain. The bond angles are also very close to the ideal...

Cyclohexane is most stable in the chair conformation. In this shape, the ring avoids angle strain because its bond angles are close to the ideal tetrahedral angle of 109.5°. It also avoids torsional strain because the bonds are arranged in a perfectly staggered way. In the chair form, the hydrogen atoms attached to cyclohexane carbons take two positions: axial and equatorial. Axial bonds point straight up or down and run parallel to the ring axis. Equatorial bonds point outward, roughly along...

stability of substituted cyclohexanes

Cyclohexane Chair Axial vs Equatorial

Cyclohexane chair conformations are shaped by the position of a substituent, and that position can change how stable the molecule is. The two chair forms of cyclohexane interconvert rapidly at room temperature. For unsubstituted cyclohexane, both chairs have the same energy and the same stability, so each appears in equal amount at equilibrium. When a hydrogen atom is replaced by a functional group, the two chair forms are no longer equal. In methylcyclohexane, the CH3 group is axial in one...

disubstituted cyclohexanes: cis-trans isomerism

disubstituted-cyclohexanes-cis-trans-isomerism

Cyclohexane Chair Stability and Bulky Groups

Disubstituted cyclohexanes can differ in both cis-trans arrangement and chair stability. In a cyclohexane ring, the substituents may sit on the same side of the ring or on opposite sides. These cis and trans stereoisomers have different physical properties, and they cannot switch into each other without breaking carbon-carbon bonds. Cyclohexane also has chair conformers, which place substituents in axial or equatorial positions. For 1,4-dimethylcyclohexane, the cis isomer has two conformers...

combustion energy: a measure of stability in alkanes and cycloalkanes

combustion-energy-a-measure-of-stability-in-alkanes-and-cycloalkanes

Why Branched Alkanes Burn More Cleanly

Alkanes are low-reactivity hydrocarbons because their C–C and C–H sigma bonds are non-polar. That is why they were once called paraffins, from the Latin words parum, meaning “too little,” and affinis, meaning “affinity.” In the presence of excess oxygen and high heat, alkanes undergo combustion to form carbon dioxide and water. Combustion is the energy source for natural gas, liquified petroleum gas (LPG), fuel oil, gasoline, diesel fuel, and aviation fuel. The heat released in this reaction,...

key terms and concepts

See how cyclohexane’s chair form avoids strain, why axial and equatorial bonds differ, and how ring flipping swaps their positions.

Cyclohexane Ring Flip and Axial Bonds | JoVE K12

organic chemistry

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Cyclohexane Ring Flip and Axial Bonds

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