Chair conformation (most stable):

• 6 axial H's (3 up, 3 down, alternating) and 6 equatorial H's
• Ring flip interconverts axial ↔ equatorial (all positions switch)
• Equatorial position preferred for bulky groups (less 1,3-diaxial strain)

Boat conformation (less stable by ~30 kJ/mol):

• Flagpole interactions (steric strain between H atoms)
• Eclipsing strain along the sides
• Twist-boat is slightly more stable than perfect boat

1,3-Diaxial strain: Axial substituent interacts sterically with other axial H's on the same face. Larger groups have greater preference for equatorial position.

A-value = -DeltaG for axial → equatorial conversion. Larger A-value = stronger equatorial preference.

• tert-butyl: ~22 kJ/mol (essentially locks the ring)
• CH3: ~7.1 kJ/mol
• Cl: ~2.2 kJ/mol