The chemistry of scents: Vetifer oil.

I have occasionally covered the topic of colours here, such as those of flowers and minerals, since it is at least possible to illustrate these using photographs or colour charts to illustrate the theme. But when Derek Lowe took a break from his remarkable coverage of the COVID pandemic to highlight a recent article on the active smelling principle in Vetifer oil[cite]10.1002/anie.202014609[/cite] I could not resist adding a tiny amount to his must-read story.

It would be great to illustrate this with an example of the scent, but digital scent technology has not yet taken off to the point of delivering these to the home.‡  So we will have to make do with a 3D model of the most active ingredient in Vetifer oil, which is species 10 in the scheme below[cite]10.1002/anie.202014609[/cite]

But first a bit of history. I wrote about one of my chemical heroes William Perkin, whose factory first produced synthetic dyes in quantities that reduced the cost of colourful fabrics to the point of affordability by most people. Less well known is that when he retired from running his factory, he devoted much of the rest of his life to experimenting in his home laboratory, where he discovered a simple and cheap synthesis of coumarin. This substance is an essential component of the so-called fougère genre of perfume and as with his discovery of synthetic dyes, the introduction of synthetic coumarin was to revolutionise the scent industry (although in this case, for other reasons, synthetic components did not reduce the price of perfumes as much as they did that of colourful clothes).

If you read Derek’s blog on the topic and peruse the diagram above, you will appreciate that Vetifer grass is the source of many essential oils and forms the basis of more than ⅓ of all fragrances. So, like Perkin, to have a synthesis of the most odiferous component, species 10 above, is a major breakthrough and one can only wonder whether new entirely synthetic variants might produce entirely new perfumes! As with flowers, changing a methyl group here or a stereochemistry there can have profound effects on the resulting properties!

2-epi-ziza-6(13)-en-3-one. Click for 3D model

The absolute configuration of 10 is not in doubt in any way, but it was done indirectly via another compound. As as an additional check (and because it is very quick to do) I add here the calculated optical rotation (at 589nm; a ωB97XD/Def2-TZVPP/SCRF=chloroform calculation) as being +106°. The measured value is +132° which is considered reasonably good agreement and certainly confirms the absolute configuration. For good measure, the calculated 13C spectrum (mpw1pw91/aug-cc-pVDZ/SCRF=choroform calculation) also matches that reported (For FAIR data of this analysis, see 10.14469/hpc/7965).

So as I noted, its a shame that the scent of 10 cannot be delivered here. But perhaps there would be health and safety issues if that were to be possible!

Around 1993 I was interested in how information about digital scents might be delivered to computers using the Media (or MIME) standard and went as far as informally proposing it be added to the seven existing primary Media types. Rather too tongue-in-cheek I fear, and as far as I know, no olefactory media type has been added to this day! However, an article relating to all of this has recently appeared.[cite]10.1016/j.isci.2021.102136[/cite] The John Bright collection illustrates the colourful aspects of clothes over the ages. Colours were not absent during e.g. the Victorian era as the collection shows, but one may presume that they were also not affordable by most of the population. In the same manner that in earlier times, eg Tyrian Purple was available only to Roman Emperors and other elites.

One Response to “The chemistry of scents: Vetifer oil.”

  1. Nick Davies says:

    Now there was, of course, Smell-O-Vision; and see the link to 4DX in the article.

    Not deliverable, even by 5G mast, to the home user, but when we are all let out to play again perhaps a lecture theatre could be equipped with such a system?

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