Final answer:
Homocyclic rings with 7 or fewer carbons can lose planarity due to puckered conformations that minimize angle and eclipsing strains. While larger rings have reduced strain, aromatic rings must be planar, as exemplified by benzene.
Step-by-step explanation:
Yes, a 7 or fewer membered homocyclic ring with unsaturated carbon atoms and a fully conjugated system can lose planarity. In the case of small and medium-sized homocyclic rings, such as cyclopropane or cyclobutane, they adopt non-planar puckered conformations to minimize angle and eclipsing strains.
Cyclopentane, for example, although very close to the ideal tetrahedral angle, has its atoms arranged in an envelop conformation to reduce torsional strain caused by eclipsing hydrogens. Cyclohexane displays two main conformations known as chair and boat, which are both more stable than any planar configuration due to the reduction of strain.
In larger rings, such as those with 14 or more carbons, the strain is significantly reduced, and planarity issues become minimal. However, in the context of aromaticity, a homocyclic ring must be planar to be considered aromatic, as seen in benzene, which is a six-membered ring with a conjugated pi system following Hückel's rule (4n + 2 pi electrons).