Free energy barriers to ring inversion of 3,3-dimethyl-, 4,4-dimethyl-, and 5,5-dimethylcycloheptene were found to be much smaller than those of corresponding benzocycloheptene derivatives but show the same trend. This observation strongly suggests that the chair conformation of both types of molecules inter-converts through the same mechanism. On the other hand, the ΔG≠ value for 4,4,6,6-tetramethyl-cycloheptene is about 3 kcal/mol out of line from that expected from a consideration of the behavior of the corresponding benzocycloheptene derivative. An explanation is offered.