Cyclohexane's chair

Section 2 of 4

A skeletal formula draws cyclohexane as a flat hexagon. The real molecule folds into what chemists call a chair.

Each corner of a flat hexagon is 120°. Each carbon in cyclohexane has 4 single bonds, 2 to carbons and 2 to hydrogens, so its bonds, just like methane's, spread out toward the corners of a tetrahedron, about 109.5° apart. A flat ring would force every C–⁠C–⁠C angle open to 120°. So the ring puckers: the carbon at one end of the chair tips up, the carbon at the other end tips down, and every angle settles at about 111°, close to methane's.

A flat hexagon on paper, and cyclohexane's real chair Left, cyclohexane drawn as a flat hexagon, with one corner marked 120 degrees. Right, the six carbon atoms of cyclohexane seen from the side: the ring is puckered. One end carbon tips up and the opposite one tips down, like a reclining chair, and the angles at each carbon are about 111 degrees. 120° drawn on paper: a flat hexagon tips up tips down the real ring: a chair, corners about 111°
On paper cyclohexane is a flat hexagon with 120° corners. The real ring, seen from the side, is a chair: one end tips up, the other tips down, and the angle at every carbon is about 111°.

The fold gives the hydrogens room too. On each carbon, one hydrogen points straight up or straight down, taking turns round the ring, and the other points outward around the ring's edge. Hydrogens on neighbouring carbons sit staggered, out of each other's way.

Cyclohexane, C₆H₁₂Six carbon atoms joined by single bonds in a ring, each carbon also bonded to two hydrogen atoms.
Cyclohexane, C₆H₁₂. Open the 3D model and turn it until you look along the edge of the ring to see the chair.

Quick check

Why does cyclohexane's ring fold into a chair?