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Scents and Sensibilities

The slightest of changes in the concentration and structure of a molecule can drastically change its scent.

It is quite amazing how very small changes in an odourant’s chemical structure can radically change our perception of its scent. For example, octanol, a synthetic compound used in perfumes and flavourings smells sweet and fruity, while its very close relative, octatonic acid, smells rancid and pungent.

Even more surprisingly, sometimes a molecule will have a completely different odour depending on its concentration. One well-known example of this phenomenon is the odour of indole—when present at high concentrations, its scent has been described as putrid, bearing the strong smell of feces and/or moth balls. This makes sense, given the fact that indole is one of the chemical compounds present in our stool. However, the exact same molecule, when diluted to very low concentrations, has a pleasant, floral smell; it is found in jasmine and orange blossoms, and is even added to some perfumes.

Then there is trans-2-butene-1-thiol, the major culprit in skunk stench. It is devastating at any concentration. How can it and its chemical cousins be neutralized? Tomato juice won't do it. That's a myth. The only thing tomato juice will do is create a mess, leaving us with the added problem of removing tomato juice from clothing, floors and walls. It will also turn white dogs pink. Luckily, there is a formula that works. Take one liter of 3% hydrogen peroxide (available in pharmacies), add one quarter cup of baking soda and 1 teaspoon liquid dishwashing detergent. Wash the cat or dog (or child) with this mixture and rinse with lots of water. Presto! The smell is almost completely eliminated. Save the tomato juice for your Bloody Mary.

Caitlin Bard is completing her Bachelor of Science with a major in neuroscience at McGill University.

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