Molecules: You'd better learn to live with them.
Pyridines and thiols are two of the stinkiest kinds of compounds you can come across in chemistry. You'd think if you put them together in a molecule, you'd have something nasty. Oddly, you don't:
Bafflingly, thiopyridine is apparently odorless. You'll notice I've drawn two structures here - this is a phenomenon called tautomerism, a special case of isomerism. This might play a role in the special non-stinkiness. Think of thiopyridine as a mixture of these two structures.
For more discussions on organo-stank, see this entry at Derek Lowe's blog. If you've never been, take a look; it's one of my favorites. A commenter at this link notes that the unusual lack of odor might be due to the fact that 2-thiopyridine prefers the thioamide tautomer (left) over the thiol tautomer (at right). Don't really have a thiol, don't really have a pyridine -- maybe this is why it all comes out in the wash. If anyone's had any experience with this compound (I haven't), leave a comment!
See you Monday!
Comments
I've been enjoying the site for a few weeks now, so I hate to be nitpicky, but tautomerism is most definitely not a special case of resonance.
Tautomers are actual constitutional isomers, differing in the attachments of atoms (for tautomers, only the position of hydrogen atoms and pi bonds are different). Different tautomers have different physical properties (though presumably in lots of cases, they are rapidply interconverting and different properties may not be measurable)
Resonance on the other hand is not a form of isomerism in any way. Resonance in a simple sense is a way of drawing several structures on paper that overall each contribute toward the actual structure which cannot be easily represented with a single Kekule structure.
The distinction is important and should be well-understood. The provided links to wikipedia on tautomerism and resonance are both very clear that one is not the other.
Anyhow, back to the molecule at hand - here's an interesting tidbit: the very closely related compound zinc pyrithione (the zinc salt of the N-oxide of 2-thiopyridine) is a common antifungal agent, used in dandruff shampoos.
Cheers.
Posted by: Russ | October 20, 2006 9:23 AM
I've always wondered what a solution of ethanethiol in pyridine would smell like - that would be the way to get the real mixture. My curiosity hasn't been able to overcome my fear, though.
Posted by: Derek Lowe | October 20, 2006 9:59 AM
"Infrared studies of tautomerism in 2-hydroxypyridine 2-thiopyridine and 2-aminopyridine" Spectrochim. Acta A 57(13) 2659 (2001)
Posted by: Uncle Al | October 20, 2006 11:41 AM
Thanks for the correction, fixed.
Posted by: MoTD | October 20, 2006 12:48 PM
The molecule pictured is NOT thiopyridine. In fact, the HC&P lists no molecule called "thiopyridine".
It is merely a thio-analog of a hydroxy pyridine. I.e., a thio-pyridone.
Posted by: kiri | October 20, 2006 7:15 PM