Molecule Builder: How Many Atoms Are Coplanar or Collinear?

Questions about how many atoms in a molecule are coplanar or collinear come down to a few rigid shapes. Ethene's C=C and benzene's ring are planar, ethyne's C≡C is linear, and methane's carbon is tetrahedral. A larger molecule is these units joined by single bonds — and single bonds can rotate.

In this builder you put molecules together from those units: replace any hydrogen with an sp³ carbon, a C=C, a C≡C, a benzene ring, a carbonyl, a carboxyl, an oxygen, an amino nitrogen, a nitro group or a halogen. The builder works out the 3D structure and gives three numbers: the atoms that are coplanar whatever the rotation, the most atoms that can be coplanar, and the longest line of collinear atoms.

Select a unit and turn it about its single bond to see the coplanar count change, or let the builder turn every bond to the conformation with the most atoms in one plane. The examples cover the molecules these questions most often use, from methylbenzene and phenylethene to buta-1,3-diene and ethanoic acid.