Chair Conformations: Energy

The chair with the most (and largest) substituents in equatorial positions is lower in energy. Axial substituents create 1,3-diaxial strain, so placing large groups equatorial minimizes steric interactions.

A-values quantify the energy cost of placing a substituent in an axial vs. equatorial position on cyclohexane. Larger A-values mean greater preference for equatorial. For example, t-butyl has an A-value of ~5.4 kcal/mol, while methyl is ~1.7 kcal/mol.

1,3-diaxial interactions are steric repulsions between an axial substituent and the axial hydrogens (or groups) on carbons two positions away. They are gauche-butane-like interactions and are the main source of axial instability.

Roughly, yes: the chair with the largest group equatorial is usually more stable. When multiple substituents compete, you need A-values to calculate the total strain for each conformer and compare.