Saturday, April 13, 2013

On Benzene

Figure 1. Snaaaaaakeeeee, a snaaaaaakeeeee!

Ahh benzene! Europeans fear it, I love the smell of it, and it can look like a snake (Figure 1)! What isn't there to love? Not to mention its qualities as a solvent, and its utility in the azeotropic removal of water from ethanol. But what I'm here to discuss today is how we draw benzene (dude, lets be honest, the Armstrong benzene is fantastic). This came up over coffee a few years ago and I decided to formalize it a little bit. If you want to play along, go ahead and draw a benzene yourself, don't think too hard, but pay attention to how you draw it. Twenty-five graduate student and postdoctoral chemists were surveyed for this blog post and the results were compiled and analyzed for your pleasure (after the jump).

Lets take a look at something simple first: the "aromatic" portion of the benzene. I believe there are three reasonable ways to draw the "middle" of the benzene: 1. with the vertical line to the left, 2. with the vertical line to the right, or 3. with a circle (Figure 2).
Figure 2. "Aromatic" portion of the benzene.
Above each molecule, you can see the analysis that arose from our lab: 84% of chemists use the lined notation. I rationalize this overwhelming majority by the fact that this makes mechanisms easier to draw. Its safe to say that if you use the circle notation you are laughed at by your fellow chemists - in fact, one first year graduate student in our lab remarked, "I remember I used to draw a circle, and then I decided to grow up." Although some may say the circle notation is quicker, they are wrong. On top of that it is less aesthetically pleasing to the poster of this blog entry. It is worth noting that users of the circle notation swear by its simplicity and speed.
Things get more complicated when we delve into the "cyclohexane" portion of the molecule (honestly, do the two portions of benzene not have more scientific names, calling it the "cyclohexane" portion is obviously kinda wrong, although you probably get the idea. Steve, help me out here, this is kind of stuff you usually know). For the purposes of this post I have adopted the following notation: the # represents the order in which the bonds are drawn and the arrow represents the direction the bond was drawn (Figure 3).
Figure 3. Woah dude!
Right off the bat we have a lot more variability! The "two sides" approach wins out with 20% of the chemists surveyed using this style - starting from the top of the ring and drawing to the bottom, twice. Coming in a close second is the left-side-to-clockwise-to-bottom drawing method at 16%. Lets see what other interesting things we can find out:
  • 52% draw the left side first
  • 40% start at the top
  • 8% draw a single up arrow
  • 4% goes in a full circle (thats me! I don't even pick up my pen, so lazy)
As a final note, I accidentally spilled some benzene into an ice filled beaker once and made a really cool looking frozen benzene disc. I was unable to reproduce this experiment in the lab (this morning), but I think a –20 ÂșC (salt/ice) would probably do the trick nicely.


  1. You may be interested in a Stuart Cantrill post on a similar topic!

    1. Hm, thanks! I didn't see that, which probably means I was reading less blogs at the beginning of graduate school than I am now. Its funny that he mentions how people draw taxol, I was trying to convince someone around lab that we should force each member of the lab to draw taxol from memory, and see how good/bad everyone does. Then put it on a public forum of course.

  2. I did a quick poll in my house. Lady friend draws them with the vertical line on left. I draw them with the vertical line on the right. Her mother is over for dinner (she's a biologist) and I asked "Draw me a benzene ring." She drew hers with a 30* turn - putting a side (vs a vertex) to the top and bottom.

  3. It's interesting to me that the "left side" first methods are 2nd and 3rd in this list.

    As someone who has studied chinese, the first thing to jump out at me was the idea of "stroke order" with chinese characters. For instance, to draw a square in chinese, you typically draw the left vertical line first, from top to bottom, followed by the top and right lines from left to right and top to bottom in a single stroke, then finally the bottom line from left to right (see demo, sixth entry down, here:

    We were taught that this was the "most efficient" method discovered by the chinese people.

    With that in mind, is there any connection between those who draw benzene using your 2nd and 3rd place methods, and what your native written language is?

    1. I'd say more than 80% of the people surveyed here use Roman/Latin alphabet in their native written languages. But at the same time, quite a significant proportion of Roman alphabet starts with drawing the left vertical line down (eg. t, p, k, l, h, b, n, m, d)

  4. Nice article! I also go in a full circle without taking the pen off the paper when drawing the ring. However, I think that the little circle for the aromatic part is not too bad, particularly for metal complexes. Wouldn't draw a Cp ligand with lines instead of the circle either.

  5. Just checked a few dozen times: I'm a "#4" benzene drawer (left side, then 'round the circle), and I make the first pi-bond on the left. But, then, I'm right-handed. My lab mate, who's left-handed, seems to do the whole thing differently.

  6. I'm definitely down as cyclohexane #4, but I could go either way for aromaticity; as a caveat, however, I interact with a benzene about as often as you do with nickel sulfate.

  7. When an aryl ring is not involved explicitly in part of a mechanism I'm drawing, especially in a chalk-and-talk kind of situation, I'll often just scribble a circle - it's easier and quicker.

  8. It all depends on the coordination mode of the benzene to the metal: eta6 complexes draw with a circle; eta4 or eta2, one of the cyclohexatriene varieties.

    In all seriousness, I mostly use the circle as did most people from my grad school and postdoc days. This is probably because we are so used to drawing circles in cyclopentadienyl ligands, where localized electron structures are awkward.

  9. Benzene is my first go-to solvent when I need to re-crystallize stuff. Sometimes benzene with cyclohexane as an anti-solvent (they have the same b.p. so they do not separate during reflux. Despite a high melting point of the two, the mix forms eutectic and does not freeze in the fridge at +4C). The reason why benzene is so much better than toluene for recrystallization is that benzene likes to form solvates (inclusion compounds) with many organic compounds - I run several times into compounds that could be only purified from benzene, as a solvate. The toxicity of benzene is a bit hyped up, in reality it is only slightly worse than CHCl3 and comparable to 1,2-dichloroethane. (It was the historic wide-spread use that made benzene a poster bad player - Europeans are also deadly scared of methyl alcohol, sometimes it must be stored in a poison cabinet and each consumed volume registered in a log book...)