WWWTP? – Nomenclature Edition

June 24th, 2012

There is nothing like a trip to my mailbox to bring a nice little blogging hiatus to a crashing halt. While attacking my pile of C&ENs, I caught this ad for TOSOH Organic Chemical Company on page 43 of the 11 June 2012 edition:

I guess the hair net and painter’s mask ensure that—unlike my Orange Chicken at Panda Express—these products arrive free of human hair. Matters of lab attire aside, what actually piqued my interest in the ad were the compounds for sale:

Sigh. That is not how I was taught to name organic compounds. My orgo professor—on the recommendation of IUPAC—told us to start by numbering the longest chain of carbons. Thus, 1-bromo-2-ethylbutane is properly named 3-(bromomethyl)pentane, and 1-bromo-2-ethylhexane should be 3-(bromomethyl)heptane.

Avid readers of ChemBark know that I love trick questions, and structures like the ones above make for great nomenclature practice. Many students will instinctively assume the carbon chain extending from left to right is the longest. When I taught orgo, I had to purchase red pens by the dozen.


20 Responses to “WWWTP? – Nomenclature Edition”

  1. Raman Says:

    Nice post, the first look does not point out the mistake, but you did, Thanks for sharing.

    :)

  2. Paul Says:

    Here the mistake is maybe not the classic “read the chain left to right” but having prioritized the one bearing the bromo substituent ?

  3. excimére Says:

    Hey now, the hair adds flavor to the orange chicken. God I want Panda Express right now. I feel disgusting after every meal but it’s sooo worth it

  4. excimére Says:

    And I, for one, could care less about nomenclature. As long as the numbering is internally consistent, who cares? (I mean, besides you.) Also, I took orgo 10 years ago (and then TA’d in GS with a prof who rightfully scoffed nomenclature as “arbitrary and unnecessary”), but I’m pretty sure I learned to number the longest carbon chain with the bromine. Could be wrong, though.

  5. The Curious Wavefunction Says:

    I don’t think the hair in the Panda Express orange chicken is human. You might want to live-blog the mass-spec and NMR analysis.

  6. Corey_student Says:

    The “bromomethyl” nomenclature is not generally taught in introductory organic courses, so these names are correct in that context. The other key question is “if I start with the name, will I arrive at the correct structure?” The answer to that is also yes, so if a student in my class had provided these names, he or she would receive quite a bit of partial credit.

  7. Hap Says:

    Some nomenclatures would name starting with the longest carbon chain that contains the primary functional group. If you thought an alkyl bromide was a functional group, then the nomenclature would be consistent and reasonable. However, I don’t think bromides are considered functional groups, so then you probably would default to your name.

    Also, IUPAC didn’t use to have a preferred name – so any way you could name the compound using their roots and locants that would give you the corrrect structure would be OK. I don’t know how they generate a preferred name.

  8. Special Guest Lecturer Says:

    Yawn. These branched alkyl chains are often used as solubilizing groups for conjugated materials and naming them in such a way that treats the group as a modular unit (as in “I introduced an ethyl hexyl chain along the polymer backbone”) is more intuitive than than the formally correct nomenclature.

    This example is a snapshot of how common names are created, which happens for nearly every compound that proves useful.

  9. Steve Says:

    While I agree that a strict application of the IUPAC rules gives the names you suggest, I’m with Hap on the fact that including the primary functional group in the chain is useful. Unlike Hap though, I would certainly consider a bromide as a functional group – its presence is almost certainly important in most of the reactions performed with this compound.

    I note that the name/structure converter in Chemdraw doesn’t have a problem with converting either name (that in the ad, or the IUPAC version) back to the right structure – and surely that kind of conversion is the most important thing in a systematic name. Consider also what happens if you move the ethyl group one carbon further from the bromide in the right hand structure – the correct IUPAC name is then ’1-bromo-3-ethylheptane’ – in terms of finding useful compounds in a catalogue (listed in alphabetical order), it then makes more sense for these to be named consistently rather than according to strict IUPAC rules.

  10. Anonymous Coward Says:

    I think that CAS nomenclature doesn’t count a bromide as a functional group, but as a substituent. YMMV, though.

    I don’t think that nomenclature matters a lot, because in many cases, a structure is worth more than a thousand characters – anyone looking to communicate a compound clearly will probably use the structure [with the caveat that some stereochemistry may be inconsistently conveyed or conveyed better in an (accurate) name than a structure - relative versus absolute stereochemistry, for example]. However, patents very much like to use names, particularly in the claims, and if you need to analyze them for some reason, having nomenclature experience is a good thing.

  11. wolfie Says:

    IF ! this world were ideal, we’d all be dead already.

  12. wolfie Says:

    In Heidelberg, we had an old associate professor specialized on nomenclature. (Remember, in Germany, once professors have a tenured position, they normally stay in their rank). He even wrote a textbook on chemical nomenclature.

    On the other hand, rumor was that he lost his house speculating with stocks on credit. Why that ?

  13. wolfie Says:

    only IUPAC, and even those change their rules, just like UEFA

  14. explosci Says:

    I have to agree with excimere….

    If it communicates what it is, fine. The names for many compounds get far too complicated when the compound gets large, so common names are far simpler to deal with.

  15. mamid Says:

    Think of 2-ethylhexanol (not 3-(hydroxymethyl)heptane)!

  16. Anon Says:

    Who knew Wolfram Alpha had a (IUPAC?) name generator? For the last branched alkylhalide of the series above: http://www.wolframalpha.com/input/?i=1-bromo-2-ethylhexane

    The internet is on Paul’s side. At least until I create a Wikipedia article for 1-bromo-ethylhexane and say otherwise.

  17. dvizard Says:

    @mamid: Here the alcohol is the highest functional group and indicates the head of the chain.

  18. psl Says:

    If it were up to me we’d all speack speech bubbles with line drawings in them.

    While the naming is wrong per IUPAC, it’s clearly unambiguous, only yielding problems if you’re searching for that particular string. …..
    Naming is cumbersome: CAS# and Smiles/inchi should sort it out.

    If you want to read an interesting book, try The Name Game about organic nomenclature history.

    http://www.amazon.com/Organic-Chemistry-Name-Game-Origins/dp/008034481X

  19. Recovering Chemist Says:

    Indeed, it is as the man says… While nomenclature isn;t my favorite thing to think about, teach or learn… I greatly value adhearnace to the IUPAC

  20. Recovering Chemist Says:

    It irritates me in the same way “text speak” does… Am I just an old fogey?


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