Methylcyclohexane: axial vs equatorial template

The two chairs of methylcyclohexane, the 1,3-diaxial CH₃/H interactions of the axial form, ΔG about 7.3 kJ mol⁻¹ (95 : 5 at 25 °C) and A-values of common groups.

What the template shows

• An axial CH₃ meets the two axial H on C3 and C5: 1,3-diaxial strain favours the equatorial chair
• The two chairs
• ring flip
• CH₃ equatorial: about 95 %
• CH₃ axial: about 5 %, two 1,3-diaxial CH₃/H clashes (dashed)
• Axial CH₃ is gauche to C3 and C5 of the ring: two 1,3-diaxial CH₃/H interactions, about 2 × 3.8 kJ mol⁻¹.
• The equatorial chair is favoured by about 7.3 kJ mol⁻¹ (the A-value of CH₃): K ≈ 19, about 95 : 5 at 25 °C.
• A-values (kJ mol⁻¹, approximate): CH₃ 7.3, CH₂CH₃ 7.5, CH(CH₃)₂ 9.2, C₆H₅ 11.7, C(CH₃)₃ about 20.
• Bigger groups prefer the equatorial position more strongly; ΔG° = −RT ln K converts an A-value into the ratio of chairs.
• Wedge = toward you, hash = away from you · every part of this figure is editable

Drawn with 7 atoms, 53 shapes – every one editable in MolDraw.

Sources

• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 16 Textbook
• Eliel & Wilen, Stereochemistry of Organic Compounds, Wiley 1994, ch. 11 Textbook