I have always used this molecule as an example to check the rendering of various molecular display options.
Caffeine - found in both tea and coffee - is an alkaloid
It is in fact 1,3,7-trimethylxanthine- in other words the purine
(a two-ring compound, similar to the bases adenine A and guanine G found in DNA and RNA) with
3 methyl (CH3-) groups
Two similar compounds are theophylline
(1,3-dimethylxanthine) and theobromine
Notice the alternating carbon and nitrogen atoms (grey and blue respectively) in the two rings.
The red atoms are oxygen (with double bonds in this view)
, and the white atoms are hydrogen.
The double bonds in the rings are essentially in the same plane, so this part of the molecule is rather flat.
The methyl groups show that hydrogen ions bonded to carbon atoms project outwards in 3 dimensions (at abut 108°).
Turn molecule through 90° [y-axis]
to show this