Ethane
C2H6Two sp³ carbons joined by a σ bond. Turn on Spin and picture the two ends twisting freely around that bond.
- C–C 1.53 Å
- C–H 1.10 Å
- ∠HCH 107°
- ∠CCH 112°
Ethane is two methane-like carbons joined together. Each carbon is sp³ hybridized: three of its sp³ orbitals bond to hydrogens, and the fourth overlaps head-on with an sp³ orbital from the other carbon. That head-on overlap makes the C–C σ bond.
Every angle around each carbon is close to the tetrahedral 109.5°. Turn on Angles & lengths to check the H–C–H and C–C–H angles, and compare the C–C bond (about 1.53 Å) with the shorter C–H bonds.
The important thing about a σ bond is that its electron density is symmetric around the bond axis, like a sausage on a skewer. Spinning one carbon relative to the other doesn’t change the overlap at all, so the two ends of ethane can rotate freely. Turn on Spin and imagine one CH₃ group turning while the other stays put. The different arrangements this rotation produces, and why some are slightly preferred, are the subject of the Conformations unit.
Ethane has no π bonds and no leftover p orbitals, so like methane it has nothing to show in those layers.
Sources
3D structure, measurements and electron clouds computed with PySCF (B3LYP/def2-SVP). Computed values can differ from measured ones by a degree or so, or a few hundredths of an ångström.