4.6 Axial and Equatorial Bonds in Cyclohexane
2 min read•may 7, 2024
are crucial in understanding molecular structure and stability. These conformations involve and , which affect how substituents interact and influence overall molecular stability.
and substituent positioning play key roles in determining the most stable conformations. Understanding these concepts helps predict molecular behavior and reactivity, essential for grasping organic chemistry principles and applications.
Cyclohexane Chair Conformations
Axial vs equatorial positions
Top images from around the web for Axial vs equatorial positions
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
Cyclohexane conformation - wikidoc View original
Is this image relevant?
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
Cyclohexane conformation - wikidoc View original
Is this image relevant?
1 of 3
Top images from around the web for Axial vs equatorial positions
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
Cyclohexane conformation - wikidoc View original
Is this image relevant?
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
3.6. Conformations of cyclic alkanes | Organic Chemistry 1: An open textbook View original
Is this image relevant?
Cyclohexane conformation - wikidoc View original
Is this image relevant?
1 of 3
- have bonds perpendicular to the plane of the ring alternate up and down with substituents pointing either straight up or straight down ()
- positions have bonds roughly parallel to the plane of the ring with substituents pointing away from the ring are less sterically hindered than axial substituents ()
- in cyclohexane are close to the ideal tetrahedral angle of 109.5°, minimizing angle strain
Ring-flipping in cyclohexane
- Ring-flipping is the rapid interconversion between two chair conformations at room temperature involves passing through a higher energy
- During ring-flipping, axial substituents become equatorial and equatorial substituents become axial ()
- The more stable conformation has the bulkier substituents in equatorial positions minimizes avoids between substituents ()
Chair conformations of substituted cyclohexanes
- :
- Draw the chair conformation with the substituent in both axial and equatorial positions
- Label the substituent as either axial or equatorial ()
- The equatorial conformation is generally more stable
- :
- have with both substituents on the same side of the ring and with substituents on opposite sides of the ring ()
- have cis isomers with both substituents axial or both equatorial and trans isomers with one substituent axial and one equatorial ()
- have both substituents either axial or equatorial and the conformation with both substituents equatorial is more stable ()
Stability and Energy
Compare the stability and energy of axial and equatorial substituents in cyclohexane
- Equatorial substituents are generally more stable than axial substituents as equatorial positions are less sterically hindered while axial positions experience greater ()
- Axial substituents have higher potential energy than equatorial substituents as between substituents increase strain and potential energy (1,3-diaxial methyl groups)
- The energy difference between axial and equatorial substituents is approximately per substituent depends on the size and nature of the substituent with larger substituents having a greater preference for equatorial positions ( vs methylcyclohexane)
Conformational Analysis and A-values
- involves studying the different possible spatial arrangements of atoms in a molecule and their relative energies
- A-values quantify the preference for a substituent to occupy an equatorial position over an axial position in cyclohexane
- Larger A-values indicate a stronger preference for the equatorial position, reflecting greater steric strain in the axial position
Key Terms to Review (37)
1,2-dimethylcyclohexane: 1,2-dimethylcyclohexane is a cyclic organic compound with two methyl (CH3) groups attached to adjacent carbon atoms on a cyclohexane ring. It is a structural isomer of other dimethylcyclohexane compounds and is particularly relevant in the context of understanding axial and equatorial bonds in cyclohexane.
1,2-disubstituted cyclohexanes: 1,2-disubstituted cyclohexanes refer to cyclohexane rings that have two substituents attached at the 1 and 2 positions. The arrangement of these substituents can have important implications for the conformational stability and reactivity of the molecule, particularly in the context of axial and equatorial bonds in cyclohexane.
1,3-diaxial interactions: 1,3-Diaxial interactions are steric hindrances between axial substituents on a cyclohexane ring and hydrogen atoms located on the same side of the ring, three carbons away. These interactions can affect the stability and chemical behavior of cyclohexane conformations.
1,3-Diaxial Interactions: 1,3-Diaxial interactions refer to the unfavorable steric interactions that occur between axial substituents located on the 1 and 3 positions of a cyclohexane ring. These interactions are an important consideration in understanding the conformations and stability of monosubstituted, disubstituted, and polycyclic molecules.
1,3-dibromocyclohexane: 1,3-dibromocyclohexane is a cyclic organic compound consisting of a six-membered carbon ring with two bromine atoms attached at the 1 and 3 positions. This molecule is important in understanding the concepts of axial and equatorial bonds in cyclohexane derivatives.
1,3-disubstituted cyclohexanes: 1,3-disubstituted cyclohexanes refer to cyclohexane rings that have two substituents or functional groups attached at the 1 and 3 positions. The positioning of these substituents on the cyclohexane ring has important implications for the orientation and stability of the molecule.
1,4-dihydroxycyclohexane: 1,4-dihydroxycyclohexane is a cyclic organic compound with two hydroxyl groups (-OH) attached to the 1 and 4 positions of the cyclohexane ring. It is an important structural feature in understanding the axial and equatorial bonds in cyclohexane.
1,4-disubstituted cyclohexanes: 1,4-disubstituted cyclohexanes refer to cyclohexane rings that have two substituents attached at the 1 and 4 positions. These substituents can be the same or different functional groups, and their orientation relative to the cyclohexane ring plays a crucial role in understanding the concept of axial and equatorial bonds.
A-Value: The A-value, also known as the Curtin-Hammett principle, is a concept in organic chemistry that describes the relative stability of different conformations of cyclic molecules, particularly cyclohexanes. It provides a quantitative measure of the steric interactions between substituents on a cyclohexane ring and their impact on the preferred conformation of the molecule.
Axial: In the context of cyclohexane, axial refers to the positions of hydrogen atoms or substituents that are perpendicular to the plane of the ring structure. These axial positions alternate up and down around the ring, creating a specific spatial arrangement.
Axial bonds: In the context of cyclohexane, axial bonds are bonds that project vertically upwards or downwards from the plane of the molecule. They contrast with equatorial bonds, which extend outwards from the ring in a more horizontal fashion.
Axial Positions: Axial positions refer to the spatial orientation of substituents or atoms in a cyclohexane ring, where they are positioned along the central axis of the ring. These positions are distinct from the equatorial positions, which are oriented perpendicular to the ring's central axis.
Bond Angles: Bond angles refer to the geometric arrangement of atoms around a central atom in a molecule, determined by the number and type of bonds formed. This concept is crucial in understanding the structures and properties of various organic compounds.
Chair Conformations: Chair conformations refer to the three-dimensional arrangements of atoms in cyclohexane and other cyclic compounds. These conformations are important in understanding the stability and reactivity of organic molecules.
Chlorocyclohexane: Chlorocyclohexane is a cyclic organic compound consisting of a cyclohexane ring with a chlorine atom substituted onto one of the carbon atoms. It is an important intermediate in the synthesis of various pharmaceutical and industrial compounds.
Cis Isomers: Cis isomers are a type of stereoisomer where two identical substituents are located on the same side of a carbon-carbon double bond or a cyclic structure. This term is particularly relevant in the context of understanding isomerism in cycloalkanes, cyclohexane conformations, and diastereomers.
Cis–trans isomers: Cis–trans isomers are types of stereoisomers where the same atoms or groups of atoms are positioned differently around a rigid structure, such as a double bond or a ring system, in cycloalkanes. In cis isomers, these groups are on the same side; in trans isomers, they are on opposite sides.
Conformational analysis: Conformational analysis is the study of the different shapes (conformations) that molecules can adopt due to rotation around single bonds. It particularly focuses on how these shapes affect the molecule's chemical properties and reactivity in organic chemistry.
Conformational Analysis: Conformational analysis is the study of the three-dimensional arrangements or conformations that a molecule can adopt. It involves examining the relative stability and interconversion of different conformations, which is crucial for understanding the behavior and reactivity of organic compounds.
Cyclohexane: Cyclohexane is a saturated, cyclic hydrocarbon compound with the chemical formula C6H12. It is a key component in understanding various aspects of organic chemistry, including the naming and stability of cycloalkanes, conformational analysis, and its role in the structure and properties of aromatic compounds and steroids.
Disubstituted Cyclohexanes: Disubstituted cyclohexanes refer to cyclohexane rings that have two substituent groups attached to the carbon atoms. These substituents can be positioned in different orientations, leading to distinct stereochemical arrangements and properties.
Equatorial: In the context of cyclohexane, equatorial refers to the positions of substituents attached to the carbon atoms in the ring, oriented around the perimeter, parallel to the equator of the molecule. These positions are more energetically favorable due to reduced steric strain compared to axial positions.
Equatorial bonds: Equatorial bonds in cyclohexane are the chemical bonds that extend outward from the center of the molecule, positioned roughly parallel to the equator if the cyclohexane ring is imagined as a globe. These bonds offer less steric strain than their axial counterparts, making them more stable in most substituent configurations.
Equatorial Positions: Equatorial positions refer to the spatial arrangement of substituents or atoms in a cyclohexane ring, where they are oriented perpendicular to the plane of the ring. This positioning is in contrast to the axial positions, which are parallel to the ring's plane.
Ethylcyclohexane: Ethylcyclohexane is a cyclic organic compound consisting of a cyclohexane ring with an ethyl group (CH3CH2-) attached. It is an important molecule in the context of understanding axial and equatorial bonds in cyclohexane derivatives.
Half-Chair Conformation: The half-chair conformation is a three-dimensional arrangement of atoms in a cyclohexane ring where the ring is not in a perfect chair conformation, but instead adopts a distorted, intermediate shape between a chair and a boat configuration.
Hydroxyl Groups: A hydroxyl group (OH) is a functional group consisting of a hydrogen atom bonded to an oxygen atom. It is a key structural feature in organic chemistry, particularly in the context of cyclohexane conformations.
Isopropylcyclohexane: Isopropylcyclohexane is a monosubstituted cyclohexane compound where an isopropyl group (a branched alkyl group) is attached to the cyclohexane ring. This term is important in understanding the concepts of axial and equatorial bonds in cyclohexane, as well as the conformations of monosubstituted cyclohexanes.
Methyl Groups: A methyl group (CH3-) is a functional group in organic chemistry consisting of a single carbon atom bonded to three hydrogen atoms. Methyl groups are important substituents in many organic compounds and play a key role in the context of understanding axial and equatorial bonds in cyclohexane.
Methylcyclohexane: Methylcyclohexane is a cyclic alkane with a methyl group (CH3) attached to the cyclohexane ring. It is a key compound in understanding the concepts of axial and equatorial bonds in cyclohexanes, as well as the conformations of monosubstituted cyclohexanes.
Monosubstituted Cyclohexanes: Monosubstituted cyclohexanes refer to cyclohexane molecules that have a single substituent group attached to the ring. This term is particularly relevant in the context of understanding the axial and equatorial bond orientations as well as the conformations of these substituted cyclohexane compounds.
Ring-flip: A ring-flip is a conformational change in cyclohexane where axial bonds become equatorial and vice versa, without altering the molecular formula. This process allows cyclohexane to relieve strain and achieve a lower energy state.
Ring-Flipping: Ring-flipping is a dynamic process that occurs in cyclohexane and other cyclic organic compounds, where the molecule rapidly interconverts between two energetically equivalent conformations. This phenomenon is crucial in understanding the axial and equatorial bond arrangements in cyclohexane.
Steric strain: Steric strain is the repulsion between adjacent atoms or groups in a molecule due to their physical size, causing a decrease in stability. This strain affects the molecule's spatial configuration and can influence its reactivity.
Steric Strain: Steric strain refers to the distortion or destabilization of a molecule caused by the repulsive interactions between bulky groups or atoms that are in close proximity within the molecule's structure. This concept is particularly relevant in the context of understanding the conformations and stability of cyclic compounds, such as cyclohexane, as well as the stability of alkenes.
Tert-butylcyclohexane: tert-butylcyclohexane is a cyclic organic compound with a cyclohexane ring and a tert-butyl substituent attached to the ring. It is an important molecule in the study of axial and equatorial bonds in cyclohexane.
Trans Isomers: Trans isomers are a type of stereoisomers that occur when two identical substituents are positioned on opposite sides of a carbon-carbon double bond or a ring structure. This arrangement contrasts with cis isomers, where the identical substituents are on the same side.