Almost all the representations of the caffeine molecule that I've come across have the two rings drawn next to each other on the horizontal axis. Any particular reason for this?

Would it be sacrilege to draw the caffeine molecule (or for that matter, any molecule), oriented in a way that makes it more aesthetically pleasing or maybe even funny? For example, turn the caffeine molecule 90° to make it look like a penguin?

Person with very basic chemistry background here. Wondering if there are IUPAC rules or conventions about structure orientation.


1 Answer 1


Wondering if there are IUPAC rules or conventions about structure orientation.

There are recommendations, which aren't really rules per se (in fact even the IUPAC nomenclature books are all technically recommendations). For "how to draw structures", the appropriate recommendations are:

Brecher, J. Graphical representation standards for chemical structure diagrams (IUPAC Recommendations 2008). Pure Appl. Chem. 2008, 80 (2), 277–410. DOI: 10.1351/pac200880020277.

which is free to read online. The relevant section is GR-3.4.2, which states (emphasis mine)

For ring systems containing at least two fused rings, that system should be presented in its preferred orientation. For most practical purposes, it is sufficient to orient the ring system so that:

  • The fused ring system is oriented more or less horizontally. A symmetry axis (or plane) should be vertical or horizontal.
  • If the system contains multiple “rows” of rings, any “extra” rings should be positioned so that they are toward the right and the top of the ring system.
  • Larger rings should be toward the left and smaller rings toward the right.
  • Heteroatoms should be toward the right and, with slight preference, toward the bottom.

So, generally, according to these specifications, caffeine would usually be drawn with both rings lined up "in a row". Of course, nothing is stopping you from drawing it differently if you wanted to do so. However, it would almost certainly look out of place in formal scientific writing.

[NB: Some people like to think that IUPAC are being a pain in the back when they make such recommendations. The truth is that by far most of these recommendations already exist as "common sense" or "conventions" to chemists, and they already obey most of them subconsciously. Furthermore, these recommendations aren't enforced by anybody, anywhere, so deviations are always possible (and do occur regularly).]

  • 4
    $\begingroup$ +1 Follow IUPAC, unless you have a good reason not to. And I like rules that contain the words "more or less". :D $\endgroup$
    – Karl
    Jan 20, 2022 at 21:47
  • $\begingroup$ +1 It's also worth mentioning that Brecher has been heavily involved in ChemDraw, so the recommendations also come from real-world experience in trying to make "nice looking" diagrams. $\endgroup$ Jan 25, 2022 at 17:20

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