MolDraw › Chemistry tools › Chair Conformation and Newman Projection Drawer
Chair Conformation and Newman Projection Drawer
In short: Pick groups for C1 to C6 of cyclohexane to draw both chair conformers with correct axial and equatorial bonds, and get the more stable chair from A-values with its population at 298 K. A second tab rotates any C–C bond in a Newman projection and plots its energy.
Use it to check homework on cis/trans-disubstituted cyclohexanes, to see a ring flip happen, or to learn why butane prefers the anti conformation. Choose each group as up (wedge) or down (dash); the tool works out which bonds are axial in each chair.
Groups on each carbon
Up = wedge (above the ring), down = dash (below). Two groups on the same face are cis; opposite faces are trans.
Dihedral angle (rotate the back carbon)
Strain values (kJ/mol)
Any group other than H uses the CH₃ values. They are good for alkyl groups and a rough guide for others.
How to use the chair and Newman drawer
- Pick an example such as trans-1,2-Dimethyl, or set an Up (wedge) and Down (dash) group for each carbon C1 to C6.
- Read both chairs. Axial bonds are orange and point straight up or down. Equatorial bonds are blue and point out from the ring.
- The results box adds up the strain of each chair (A-values, 1,3-diaxial clashes and gauche interactions), gives ΔG, K and the % of each chair at 298 K.
- Press Animate ring flip to watch every axial group become equatorial. Use Download SVG or Download PNG for notes.
- Open the Newman projection tab, choose a molecule, and move the slider or press +60° to step between staggered and eclipsed forms. The energy plot follows the dihedral angle.
Axial and equatorial bonds in the chair
Cyclohexane is not flat. It folds into a chair with all C–C–C angles close to 109.5° and every C–H bond staggered, so it has almost no ring strain. Each carbon has one axial bond, parallel to the ring axis (straight up or straight down), and one equatorial bond, pointing out around the ring's equator.
- Axial bonds alternate up, down, up, down around the ring.
- Each equatorial bond is parallel to the ring bonds one carbon away.
- On any carbon, the axial and equatorial bonds point to opposite faces: if axial is up, equatorial is slightly down.
Ring flip
At room temperature the ring flips about 105 times per second (barrier about 45 kJ/mol). In the flip, every axial bond becomes equatorial and every equatorial bond becomes axial, but up stays up and down stays down. So cis and trans never change on a ring flip.
A-values and 1,3-diaxial strain
An axial group bumps into the two axial hydrogens on the same face, three carbons along (1,3-diaxial interactions). The A-value is the free energy cost of having the group axial instead of equatorial.
| Group | A-value (kJ/mol) | % equatorial at 298 K |
|---|---|---|
| F | 1.0 | 60% |
| Cl | 2.2 | 71% |
| Br | 2.0 | 69% |
| OH | 3.6 | 81% |
| NH₂ | 5.9 | 92% |
| CH₃ | 7.3 | 95% |
| CH₂CH₃ | 7.5 | 95% |
| CH(CH₃)₂ | 9.2 | 98% |
| C₆H₅ | 11.7 | 99% |
| C(CH₃)₃ | 20.5 | >99.9% |
Then ΔG = −RT ln K, where K = [chair 2]/[chair 1]. At 298 K, RT = 2.48 kJ/mol, so every 5.7 kJ/mol changes K tenfold.
How the tool adds up strain
- Each axial group adds its A-value.
- Two groups (not H) axial on the same face, 1,3 to each other, add about 8 kJ/mol more (the CH₃/CH₃ clash is about 15.4 kJ/mol in total).
- Two carbon groups on neighbouring carbons that are gauche (equatorial–equatorial or axial–equatorial) add 3.8 kJ/mol, like gauche butane. Diaxial neighbours are anti, so they add nothing.
These are additive textbook estimates. Polar groups can also feel hydrogen bonding or dipole effects that the simple sum leaves out.
Newman projections, staggered and eclipsed
A Newman projection looks straight down one C–C bond. The front carbon is a point where its three bonds meet; the back carbon is a circle with its bonds starting at the edge. The angle between a front bond and a back bond is the dihedral (torsion) angle.
- Staggered (60°, 180°, 300°): back bonds sit between front bonds. Lowest energy.
- Eclipsed (0°, 120°, 240°): back bonds hide behind front bonds. Highest energy, from torsional strain plus steric strain.
- Anti: the two largest groups 180° apart. Gauche: 60° apart.
| Interaction | Energy (kJ/mol) |
|---|---|
| H/H eclipsed | 4.0 |
| H/CH₃ eclipsed | 6.0 |
| CH₃/CH₃ eclipsed | 11 |
| CH₃/CH₃ gauche | 3.8 |
Butane (C2–C3): anti 0, gauche 3.8, eclipsed (CH₃/H twice + H/H) 6 + 6 + 4 = 16, fully eclipsed (CH₃/CH₃ + 2 H/H) 11 + 4 + 4 = 19 kJ/mol. Ethane: 3 × 4.0 = 12 kJ/mol barrier.
Worked examples
Methylcyclohexane
Chair with CH₃ axial: 7.3 kJ/mol. Chair with CH₃ equatorial: 0. K = e7.3/2.479 = 19.0.
95% equatorial, 5% axial
trans-1,2-Dimethylcyclohexane
Diequatorial chair: one gauche CH₃/CH₃, 3.8. Diaxial chair: 2 × 7.3 = 14.6. ΔG = 10.8 kJ/mol.
Diequatorial, 98.7%
cis-1,3-Dimethylcyclohexane
Diequatorial: 0. Diaxial: 2 × 7.3 + about 8 for the CH₃/CH₃ 1,3-diaxial clash = 22.6 kJ/mol.
Diequatorial, more than 99.9%
cis-1,4-Di-tert-butylcyclohexane
Each chair has one tert-butyl axial (20.5 kJ/mol). A twist-boat with both groups pseudo-equatorial costs a similar amount.
The ring leaves the chair for a twist-boat
Butane, gauche vs anti
Gauche is 3.8 kJ/mol above anti. With two gauche forms, K = 2e−3.8/2.479 = 0.43.
About 70% anti, 30% gauche at 298 K
Common mistakes
- Thinking a ring flip turns cis into trans. It never does: up stays up.
- Saying "cis means both axial". In 1,2- and 1,4-disubstituted rings, cis is axial–equatorial; in 1,3-rings cis is diequatorial or diaxial.
- Drawing axial bonds tilted. Axial bonds are vertical; equatorial bonds are parallel to the ring bonds one carbon away.
- Adding A-values from both chairs. Each chair only pays for the groups that are axial in it.
- Forgetting gauche butane interactions between groups on neighbouring carbons (trans-1,2 diequatorial still has one).
- Using °C instead of kelvin in ΔG = −RT ln K.
Draw it for your notes. Open the free MolDraw editor to draw chairs from the ring templates, add wedges and labels, and export a PNG or SVG.
Open full MolDraw editorFrequently asked questions
What is the difference between axial and equatorial?
Axial bonds are parallel to the axis of the chair and point straight up or straight down. Equatorial bonds point outward, roughly in the plane of the ring. Each ring carbon has one of each, and they point to opposite faces.
Why is the equatorial position more stable?
An axial group is close to the two axial hydrogens three carbons along on the same face (1,3-diaxial interactions). An equatorial group points away from the ring and avoids them. For a methyl group the difference is 7.3 kJ/mol.
What is an A-value?
The A-value is the free energy difference between a monosubstituted cyclohexane with the group axial and with the group equatorial. Larger A-values mean a stronger preference for equatorial: F 1.0, OH 3.6, CH3 7.3, tert-butyl about 20.5 kJ/mol.
How do I work out the percentage of each chair?
Find ΔG between the two chairs, then use K = e^(−ΔG/RT) with R = 8.314 J/(mol·K) and T in kelvin. The fraction of the more stable chair is K/(1 + K) when K is above 1. For methylcyclohexane K = 19, so 95% equatorial.
Does a ring flip change cis to trans?
No. A ring flip swaps axial and equatorial on every carbon, but a group that points up stays up. Cis and trans depend only on which face each group is on.
Why is the anti conformation of butane the most stable?
In the anti form the two methyl groups are 180° apart and every bond is staggered. Gauche butane is 3.8 kJ/mol higher because the methyls are 60° apart, and the eclipsed forms are 16 and 19 kJ/mol higher.
Is the chair and Newman drawer free?
Yes. It runs in your web browser with no sign-up, and you can download every drawing as SVG or PNG.
Related chemistry tools
Last updated: