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How does rotation around a single bond produce different molecular conformations?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

Rotation around a single bond creates different molecular conformations—infinite spatial arrangements of atoms—because atoms attached to the bonded carbons can occupy varying positions relative to one another.1

These arrangements are not all equal in energy. Because of attractive and repulsive forces between atoms, different conformations represent states of varying potential energy. For example, in ethane, the staggered conformation is more stable (lower energy) than the eclipsed conformation, where electron repulsion between bonds increases energy.12

When these rotational barriers are high enough, the resulting structures can be isolated as stable conformational isomers. In more complex molecules like cyclohexane, these rotations allow the ring to distort into low-energy shapes, such as the "chair" form, to minimize torsional and angle strain. Ultimately, whether these conformations are considered distinct isomers depends on the energy required to interconvert them and the timescale of observation.23