In a chair conformation of cyclohexane, when a substituent is placed in an equatorial position, it is always more stable than when it is in an axial position.

In a cyclohexane chair, each carbon can hold a substituent either pointing outwards (equatorial) or up and down (axial). Axial groups clash with other axial hydrogens on the same side of the ring, creating 1,3‑dipolar steric strain that raises the energy. Equatorial groups avoid these close contacts because they lie in the plane of the ring and are farther from other substituents. Thus an equatorial substituent is lower in energy and more stable. For example, a methyl group on carbon 1 prefers the equatorial position over the axial one because the axial position would force it into a steric clash with the axial hydrogens on carbons 3 and 5.