We’re nearing the end of yet another exciting year of chemistry, one full of ups, downs, and innnumerable other clichés. Since it looks like Paul has better things to do than blog nowadays (dude, Paul, we all do, but people actually read YOUR blog), my hizzy psi-stizzy and I are going to do our own little award thingee, similar to the Chemmys but less controversial and probably less fun. But ours has a better name:

Yes, the Cornies. If it’s Corny-worthy, we’ll be talking about it in the next week or so. Starting off the festivities is the award for best supporting actress Molecule of the Year. There have been many great molecules made this year, but none deserve as much attention and celebration as this year’s winner. 

The diaza[12]annulenes are this year’s winner for molecule of the year, because no one managed to actually make them. Now, of course, a lot of molecules weren’t made this year, but no molecules, aside from maybe maitotoxin, were not made with as much pomp and press as the diaza[12]annulenes. They even managed to make it into the popular German news magazine Der Spiegel. This is mostly because two separate groups said they did, then, as it turns out, they didn’t, and instead made pyridinium salts that have been known for nearly 100 years.

Here’s what the Yamaguchi and Menger groups were, in general, proposing:

Now I have to admit that I didn’t may much attention to these papers when they came out. But at a first glance, this chemistry is like Sea World, it’s so fishy. First, you break an aromatic ring (pyridine) to form some linear product which, through some act of God, cyclizes to form the potentially antiaromatic [12]annulene (if it’s planar, which, as Mitch mentioned, no way in hell it will be- [4n]annulenes will distort themselves to be as nonplanar and thus non-antiaromatic as possible).

Okay. Undoubtedly, if we were to draw an energy diagram, the product would be uphill in energy, I think. You break aromaticity to make some not-really conjugated polyene. Now I suck at p-chem, but my o-chemist’s intuition says that if you were to actually make that, you’d have to have it under kinetic conditions- low temperatures and whatnot. But the conditions call for refluxing ethanol overnight- pretty thermodynamic conditions to me. Of course, their pyridine ring-opening mechanism has been demonstrated before- noone would propose such a preposterous mechanism without prior evidence- from a 1974 issue of the illustrious Collection of Czechoslovak Chemical Communications. Very fishy, in my opinion. One doesn’t even need to look at the NMR spectrum to be a bit skeptical, but the NMR was pretty fishy too.

Manfred Christl sure thought so. In an unusually direct comment in Angewandte Chemie, he details how they actually made pyridinium salts through a known reaction (the Zincke Reaction) that turned 103 years-young this year. (T. Zincke, Justus Liebigs Ann. Chem. 1904, 330, 361-374; T. Zincke, G. Heuser, W. Möller, Justus Liebigs Ann. Chem. 1904, 333, 296-345. I’m not kidding.) So Christl schools them, and us, on the actual reaction, which seems much more reasonable:Basically, I think there’s a really good rule when it comes to annulene research, and it’s one, I think, good annulene chemists know about, but I think it’s a good rule if you’re ever going to make them:

GET A FUCKING CRYSTAL STRUCTURE!

NMR just isn’t good enough for these beasts. They’re tricky and sometimes unpredictable.

So congratulations diaza[12]annuluene: your existence has still yet to become known. And let this be a lesson to all of you: make a funky aromatic? Get a crystal structure. Or if that’s too much work, you can just send it to the reviewers of these papers.

Props to Derek Lowe’s excellent blog posts on the matter for filling me in. If you don’t read In The Pipeline, you really should.

This entry was posted on Wednesday, December 19th, 2007 at 12:31 am and is filed under Cornies, announcements. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.