24Q2 **COPY PASTE**
""In the past, chemists believed that cycloalkanes, including cyclohexane, were planar, like benzene (see below). Since the ∠C-C-C bond angle of sp3 hybridized carbon chain is 109o28', cycloalkanes will suffer from some strain if these are to be planar. All cycloalkanes, except for cyclopentane, become unstable because of this strain (Baeyerﾕs strain theory). According to this theory, the most stable cycloalkane is cyclopentane, and cyclohexane is the next.
Although this theory could explain the high reactivity of cyclopropane, it gradually turned out that cyclohexane could be more stable if the nonplanar structure was assumed. By taking the nonplanar structure, the ∠C-C-C bond angle of cyclohexane could maintain the tetrahedral angle. Because of the cyclic nature, the number of structures cyclohexane can take is much less as compared with its acyclic analog hexane. There is, however, flip-flop of the ring as the rotation about the C-C bond of cyclohexane takes place. The movement of the ring can most conveniently revealed by the torsion angle made by four successive carbon atoms (butane unit) arbitrarily chosen. If we choose C1~C4 (1) as the butane unit, the torsion angle can be defined as is shown in 2. You should confirm the discussion above by using a molecular model.""
