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Watch this to appreciate the science of fragrances for Higher Chemistry (and why little boys loves oranges)

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Have you ever squeezed an orange skin?

When I was a kid, we used to spray each other and to this day opening a fresh orange remind me of these orange peel fights.

A bit silly and childish but hey everybody does stupid things when they’re 7 or 8. I could still smell orange on my hands and clothes hours after. Which was really nice.

But how come these tiny droplets spread from just the surface of not just oranges but also lemons, grapefruits and any citruses can have such a powerful scent?

Citruses peels have been used for fragrance extraction for millennia. The food industry, perfume industry, cleaning product industry use combinations of these complex chemicals called essential oils in their products to produce their identities.

So, let’s follow the scent and see where it takes us..

This is thinkfour.

Essential oils are concentrated extracts from plants.

They are not just from citrus peels, they can be extracted from almost any part of a large variety of plants like the flowers of lavender or the bark of cinnamon tree. They have a large range of uses:
- Essential oils from lavender, rosemary, peppermint, cinnamon, ginger or oregano can be used in cooking

Essential oils can obviously be used in parfums. Their composition is a well-guarded secret. For example, Chanel No. 5 contains Bergamot, Lemon, Jasmine, Rose, Ylang Ylang, Cedarwood, Vanilla and more but I would be incapable of giving you the exact quantities.

Essential oils have also been used for centuries for their medicinal properties. Tea tree oil is used as an antiseptic.

They are usually, like edible oils, insoluble in water. They are also volatile meaning they easily evaporated at room temperatures making them easy to diffuse and parfum a room.

Essential oils mostly contain a family of compounds known as terpenes.

This family of chemicals are based on isoprene units joined together. Terpenes are then going to be a multiple of this C5H8 unit repeating n times. Terpenes with all number of isoprene units are found in nature. For example, they can be as small as 2 isoprene units like Limonene (found in citrus), Carvone (found in spearmint) or Myrcene (a terpene responsible for woody smell). But they can also be as large as 6 isoprene units joined together to form terpene like squalene (found in shark oil).

Terpenes can be altered over time to form new compounds which will have different properties. This is why most essential oil will have a use-by date on their bottle.

The culprit? Oxygen. Indeed, terpenes can undergo an oxidation reaction. Some of these new oxidised compounds will be desirable to form new fragrances and properties. The peppermint flavour for example comes from a terpene called menthol AND its oxidation counterpart, menthone.

Both compounds will contribute to the peppermint aroma we are so familiar with. But in other cases, it can be more problematic, even harmful. Alpha terpene present in tea tree oil will react with the oxygen present in the air to form ascaridole and p-cymene and these oxidation products have been linked with allergic reaction to tea tree oil. To counter these unwanted reactions, essential oils are usually stored in sealed brown bottles to avoid contact with oxygen and reduce exposure to light which can be a trigger.

So that is what I was childishly playing with all these years ago.

Natural chemicals, produced by plants that offer us these lush and diverse fragrances.

Next time you bite into a nice and juicy orange, slice a lemon while cooking, pick-up a couple of leaves of mint from the garden or rub a couple of lavender flowers between your fingers, take a second to appreciate some of these natural chemicals and smell the fragrances that essential oils have to offer.

Understanding this stuff might bring you the sweet smell of success in Higher Chemistry.

This was Think Four. Thanks for watching.