Why is chair conformation of cyclohexane more stable

The same is true for the equatorial positions. A second, much less stable conformer is the boat conformation. This too is almost free of angle strain, but in contrast has torsional strain associated with eclipsed bonds at the four of the C atoms that form the side of the boat.

In addition, a steric interaction of the H atoms inside the "bow" and the "stern", known as the flagpole interaction also destabilises the boat. A third conformation is produced by twisting the boat to give the twist or skew-boat conformation. The twist relieves some of the torsional strain of the boat and moves the flagpole H further apart reducing the steric strain. Consequently the twist boat is slightly more stable than the boat.

Another exception is the amino alcohol below. What force might be responsible for the fact that the axial conformer is favoured in equilibrium conditions?

This is a topic commonly taught to undergraduates in Organic Chemistry. A- values are empirically derived and denote the thermodynamic preference for a substituent to be in the axial or equatorial position in cyclohexane.

A -values can be added, and the total energy thus derived gives the difference in free energy between the all-axial and all-equatorial conformations. In the trans, actually! Thanks for all these amazing materials! This was very helpful to me. I appreciate this because i am studying organic chemistry right now. Hi James, I realized that two of the conformers in the ranking of the 4 are identical. May be helpful for others in the future.

Thanks for the help with the other information though. Also, it will be really helpful if you could tell whether the net dipole moment of the molecule plays a part in its stability. I learn a lot from your content. Yes, with extremely bulky equatorial groups van der Waals strain can arise, which will push the equilibrium toward the diaxial conformer. In the case of trans 1,2-di-butyl cyclohexane, the diaxial conformer was calculated to be 6.

Interestingly, a twist-boat conformation was very close to it in energy. In the case of dipole moments, you could test that by measuring conformational preferences as a function of polarity of the solvent.

This can be done in NMR, for example. I looked into the effects of solvent on A values i. Rather, they are pointing away from each other. Thank you for the helpful content. The reason we do not want ring strain and steric hindrance is because heat will be released due to an increase in energy; therefore, a lot of that energy is stored in the bonds and molecules, causing the ring to be unstable and reactive.

Another reason we try to avoid ring strain is because it will affect the structures and the conformational function of the smaller cycloalkanes. One way to determine the presence of ring strain is by its heat of combustion.

By comparing the heat of combustion with the value measured for the straight chain molecule, we can determine the stability of the ring. Bond angle strain causes a ring to have a poor overlap between the atoms, resulting in weak and reactive C-C bonds. An eclipsed spatial arrangement of the atoms on the cycloalkanes results in high energy. With so many cycloalkanes, which ones have the highest ring strain and are very unlikely to stay in its current form?

The figures below show cyclopropane, cyclobutane, and cyclopentane, respectively. Cyclopropane is one of the cycloalkanes that has an incredibly high and unfavorable energy, followed by cyclobutane as the next strained cycloalkane. Any ring that is small with three to four carbons has a significant amount of ring strain; cyclopropane and cyclobutane are in the category of small rings.

A ring with five to seven carbons is considered to have minimal to zero strain, and typical examples are cyclopentane, cyclohexane, and cycloheptane. However, a ring with eight to twelve carbons is considered to have a moderate strain, and if a ring has beyond twelve carbons, it has minimal strain. Most of the time, cyclohexane adopts the fully staggered, ideal angle chair conformation.

In the chair conformation, if any carbon-carbon bond were examined, it would be found to exist with its substituents in the staggered conformation and all bonds would be found to possess an angle of Cyclohexane in the chair conformation. In the chair conformation, hydrogen atoms are labeled according to their location. Those hydrogens which exist above or below the plane of the molecule shown with red bonds above are called axial. Those hydrogens which exist in the plane of the molecule shown with blue bonds above are called equatorial.

Although the chair conformation is the most stable conformation that cyclohexane can adopt, there is enough thermal energy for it to also pass through less favorable conformations before returning to a different chair conformation.

When it does so, the axial and equatorial substituents change places. The passage of cyclohexane from one chair conformation to another, during which the axial substituents switch places with the equatorial substituents, is called a ring flip. Methylcyclohexane is cyclohexane in which one hydrogen atom is replaced with a methyl group substituent.

Methylcyclohexane can adopt two basic chair conformations: one in which the methyl group is axial, and one in which it is equatorial. Methylcyclohexane strongly prefers the equatorial conformation. This is to be compared with boat and twist-boat conformations whose substituents tend to eclipse each other to give unfavourable steric interactions.

This answer is no substitute for actually making a model, and observing trans-annular interactions in three dimensions. Why is a chair conformation of cyclohexane more stable?

Jul 30, Because it minimizes so-called trans-annular interactions.