1. Choose an isomer
2. Choose a chair (ring flip)
⇌
Strain bookkeeping uses the usual teaching values: 0.9 kcal/mol per CH3/H 1,3-diaxial contact (two per axial methyl, equal to one gauche-butane interaction), 0.9 per gauche CH3/CH3 on adjacent carbons, and 3.7 for a CH3/CH3 1,3-diaxial contact. Populations are for 25 °C.
Distance between any two atoms
to
Or click any two atoms in the 3D model. Ring hydrogens are named H1ax, H1eq and so on; methyl carbons are Me1, Me3 (Me1′ for the second methyl on C1).
Key distances in this chair
Ideal geometry used in the model
| C–C bond length | 1.54 Å |
| C–H bond length | 1.09 Å |
| Every bond angle | 109.47° |
| Ring dihedrals | ±60° |
| Axial bonds | parallel to the ring axis |
The chair is a fragment of the diamond lattice, so every carbon, including the methyl carbons, sits on a lattice point. Real rings flatten slightly (ring dihedrals about ±55°), and a diaxial CH3/CH3 pair would push apart. The model shows the idealized values on purpose.
How to use the 3D model
- Drag to rotate, scroll or pinch to zoom.
- Click 2 atoms for a distance, 3 for an angle, 4 for a dihedral.
- Top view looks down the ring axis: axial bonds point straight at you.
Exercise: count the gauche interactions
Every C–C–C–C dihedral at ±60° counts, including the six inside the chair itself. Compare axial and equatorial: the difference × 0.9 kcal/mol is the textbook estimate of the A-value.
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ring C methyl C H
Click atoms to measure.