The ring flip of cyclohexane does one very significant thing:  it exchanges axial and equatorial positions.  Compare the two structures below and make a model that has some identification to distinguish axial and equatorial positions.  cyclohexane_1.pdb cyclohexane_2.pdb Page controls: Black background White background Spacefilling model Wireframe Ball & Stick For cyclohexane itself, this does not make much difference.  On the other hand, when there is a substituent like a methyl group, it makes a big difference, because the structural relationship between the methyl group and other parts of the molecule changes: Me_Cyclohexane_eq.pdb Me_Cyclohexane_ax.pdb The energy difference, 1.8 kcal/mol, arises from the 1,3 diaxial interactions between the methyl hydrogens and the other axial hydrogens.  This is greater than the interactions with flanking equatorial hydrogens in the equatorial conformer.  The energetic cost of these 1,3-diaxial interactions is general, and varies according to the bulk of the group (and to a smaller extent, the polarity of the bond).  The cost of placing a group axial is called the "A value" and represents ΔG° between axial and equatorial forms. Substituent A, kcal/mol (kJ/mol) Keq = [equatorial]/[axial] Closest contact (axial), Å Methyl 1.8 (7.5) 18 2.38 Ethyl 1.8 (7.5) 21 2.34 2-Propyl 2.1 (8.8) 35 2.34 tert-Butyl >4.5 (>20) ("locked" equatorial) 4800 2.18 Cl 0.53 (2.2) 2.4 2.90 Br 0.59 (2.9) 2.2 2.97 I 0.47 (2.0) 2.2 3.03 OMe 0.6 (3.0) 2.2 2.74 CCH 0.5 (2.1) 2.0 2.91 For an exhaustive list of A values, see Wikipedia. Try making models of cyclohexane with different substituents and make sure you can locate the axial-axial interactions and make sense of the table shown here. Viewing as "Spacefilling" highlights the true steric demand of each substituent.