The internal angles of a regular, flat hexagon are 120°, while the preferred angle between successive bonds in a carbon chain is about 109.5°, the tetrahedral angle. Therefore, the cyclohexane ring tends to assume certain non-planar (warped) conformations, which have all angles closer to 109.5° and therefore a lower strain energy than the flat hexagonal shape. The most important shapes are chair, half-chair, boat, and twist-boat. Their relative stabilities are: chair > twist boat > boat > half-chair. All relative conformational energies are shown below. The molecule can easily switch between these conformations, and only two of them—"chair" and "twist-boat"—can be isolated in pure form.