B.R.S.M. When all you have is a hammer everything looks like a nail


Superlatives 3: The Longest Polyene

Update 02-12-12: If anyone wants/needs a copy of the original image without the text and arrow added, you can find it here.


Some of you may remember this synthesis of the world's longest polyene from a few months ago, covered by See Arr Oh here. I'm not going to say much about the the chemistry of this synthesis (Wittigs. Shedloads of 'em), or its significance, but I'd like to post a little addendum to the work here.

From Org. Lett., 2012, 14, 5496

I just got an email from a friend of mine who, upon reading the paper, asked the obvious question 'but what colour is it?'. Lycopene, of course, is famously red:

Image partly from wikipedia.org

Unable to find a answer to the question in the paper itself, or the Supporting Information he contacted the authors. After a few days, they sent a short reply and a beautiful image:

'the longest polyene is best represented by the vial on 7th from the left'

Now, how often do organic chemists get colours like that?

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  1. depends on the chemistry. One of the first labs I worked in had a project that was based on conjugate addition of amines to unsubstituted o-benzquinone. The ultimate products of the all-in-one-pot addition/reoxidation sequence are 4,5-diamino-1,2-benzoquinones which are deep blue. The intermediates and sideproducts have their own distinct colors too. I remember staring on a spinning Chromatotron disk, with zones of stark blue, red, green, yellow products slowly spreading across..

  2. Colours like this is why I miss carotenoid chemistry so much. Interestingly, one drop of some dilute trifluoroacetic acid would give carbocations with abs. maximum way up in the NIR-region – giving an essentially colourless solution. Herein lies an opportunity for another superlative-laden paper…

  3. I work up my Sonogashira’s with saturated ammonium chloride, which gives me awesome blue-yellow biphasic mixtures reminiscent of an upside-down Ukraine flag.

  4. I remember making a dibenzoquinone with 4 tBu groups on (a compound used by Knochel in oxidative coupling of Grignard reagents, easily made by aerial oxidation of 2,6-di-tert-butylphenol in basic medium), that gave a bright yellow colour in DCM, even at very low concentrations, and which crystals are deep purple.

    Reminds me Prof John Murphy (from Strathclyde) describing a compound as “more purple than purple istelf, KMnO4 doesn’t even qualify in the competition”

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