Rotations such as these are not possible in cycloalkanes, where the ring constrains the movements around the carbon-carbon single bonds. Cyclopropane rings are generally flat and have little conformational flexibility. The flexibility of four- and five- membered rings is signif icantly greater and these molecules exist as a dynamic equilibrium among various puckered conformations, as shown below• Rotations such as these are not possible in cycloalkanes, where the ring constrains the movements around the carbon-carbon single bonds. Cyclopropane rings are generally flat and have little conformational flexibility. The flexibility of four- and five-membered rings is significantly greater and these molecules exist as a dynamic equilibrium among various "puckered" conformations, as shown below