 From this observation, it is clear that there are other possible electronic interactions that stabilize the axial conformation.It is important to note that A-values do not predict the physical size of a molecule, only the steric effect.For example, the "tert"-butyl group (A-value=4.9) has a larger A-value than the trimethylsilyl group (A-value=2.5), yet the "tert"-butyl group actually occupies less space.