Following is a chair conformation of cyclohexane with the carbon atoms numbered 1 through \(6 .\) (a) Draw hydrogen atoms that are above the plane of the ring on carbons 1 and 2 and below the plane of the ring on carbon 4 . (b) Which of these hydrogens are equatorial? Which are axial? (c) Draw the alternative chair conformation. Which hydrogens are equatorial? Which are axial? Which are above the plane of the ring? Which are below it?

In the three-dimensional structure of cyclohexane, each carbon atom has two hydrogen atoms attached to it, one in an equatorial position and one in an axial position. The equatorial position extends out to the sides, almost parallel to the ring's plane, making them less sterically hindered by neighboring groups. The axial position, on the other hand, points directly above or below the plane of the ring, which can lead to higher energy conformations due to steric clashes, especially when bulky groups are attached.

For example, when drawing the chair conformation, hydrogens on carbons 1 and 2 can be positioned equatorially, sticking out to the sides, away from adjacent carbon atoms, minimizing repulsive interactions. The hydrogen on carbon 4, if depicted in the axial position, points vertically and can be drawn above or below the plane of the ring depending on the chair's orientation.

Cyclohexane exhibits conformational isomerism, which refers to the existence of different three-dimensional shapes that a molecule can adopt due to rotations around single bonds. The classic example is the switching between the chair conformations, known as ring-flipping. This isn't creating a new molecule but rather the same molecule in a different orientation. Each chair conformation has its unique distribution of axial and equatorial positions. In one chair form, a particular hydrogen might be equatorial, but after a ring flip, that same hydrogen becomes axial, altering the energy and potential interactions of the molecule.

The chair conformation of cyclohexane is the most stable due to minimal torsional strain and the most staggered arrangement of hydrogen atoms. Despite this, the cyclohexane ring is in constant motion at room temperature, flipping between these conformations, where axial hydrogens become equatorial and vice versa, demonstrating the dynamic nature of conformational isomerism in cyclohexane.

The cyclohexane molecule comprises six carbon atoms arranged in a ring, each carbon atom bonded to two other carbons and two hydrogens. This simple cycloalkane's most stable form is a puckered ring called a chair conformation, which reduces angular strain and torsional strain found in the flat hexagonal (planar) arrangement.

The alternation of carbons above and below the plane of the ring in a chair conformation avoids the eclipsing of bonds and gives cyclohexane its characteristic 3D shape. This puckered conformation allows for the hydrogens attached to the carbons to have the equatorial and axial orientations discussed previously. Each time we 'flip' the chair to its alternate conformation, we provide cylohexane with the ability to balance different types of steric interactions, which is a fundamental concept in understanding the three-dimensional geometry of molecules.