This track tackles a subtle but heavily tested idea: molecules with the same connectivity can adopt many different shapes simply by rotating around their single bonds, and these different shapes — called conformations — differ in energy. Nothing breaks; you are only twisting. Because a sigma bond allows free rotation (Track 1), a molecule is constantly flexing between conformations, spending most of its time in the lowest-energy (most stable) ones.

For simple chains, we analyze rotation with a Newman projection — a way of drawing the molecule as if you are sighting straight down one C–C bond. The front carbon is shown as a dot with three bonds radiating out; the back carbon is a circle with three bonds. As you rotate the back carbon relative to the front, you cycle through key arrangements:

Staggered conformations have the front and back bonds offset by 60°, as far apart as possible. These are low-energy and stable because the bonding electrons are maximally separated. The most stable of all is the anti conformation, where the two largest groups sit 180° apart.
Eclipsed conformations have front and back bonds directly overlapping (0° offset). These are high-energy because of torsional strain (electron repulsion between overlapping bonds) and, when large groups eclipse, added steric strain from crowding. The worst case is the fully eclipsed conformation with the two largest groups on top of each other.

The molecule rocks continuously between these, but favors the staggered/anti arrangements.

For cyclohexane, the same energy-minimizing logic produces the famous chair conformation — the puckered shape that eliminates angle and torsional strain, making cyclohexane so stable. On a chair, each carbon has two distinct positions for its attached groups: axial (pointing straight up or down, parallel to the ring's axis) and equatorial (pointing outward around the ring's "equator"). Cyclohexane rapidly interconverts between two chair forms in a process called a ring flip, and here is the punchline that exams love: when the ring flips, every axial group becomes equatorial and vice versa. The stability rule that follows is essential — large substituents strongly prefer the equatorial position, because an axial substituent is crowded by other axial groups on the same face of the ring (called 1,3-diaxial strain). So the more stable chair is the one with the bulkiest group(s) equatorial. Being able to draw both chairs, perform the flip, and identify which is lower in energy is a core testable skill.

"Chair Flip"