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Skip to 0 minutes and 6 secondsIn our stressful hectic lives, how nice to have perfumes and fragrances to brighten-up our days, from a splash of cologne, to a sniff of freshly laundered clothes or a scented candle. Our tour of chemical attraction starts by seeing that perfumes are composed, much like musicians compose music. We see why Chanel No 5 is a landmark perfume, and how a key component aldehyde is made in the lab - today, of the 3000 or so fragrance ingredients available, more than 95% are in made in the lab. Amazingly, flowers produce around 1700 fragrance compounds.

Skip to 0 minutes and 43 secondsWe will explore those found in 'the queen of flowers', the rose; from how to extract fragrances from the petals to determining the structures of floral-smelling compounds including rose oxides. It has been suggested that the human nose can distinguish more than 1 trillion different smells. But, how do we recognise such different smells - an interesting question and, one, we will see, that current theories cannot fully explain. What we think of as a single smell is actually a combination of many odour molecules acting on a variety of receptors in our nose, but more research is needed.

Skip to 1 minute and 19 secondsWe are not the only creatures that smell - we will see that even the slightest whiff of a sex pheromone can attract some insects, while alarm pheromones can warn them of danger, and trail pheromones allow wandering ants to return to their nest. We will also consider human pheromones - a complicated and controversial area of research. The lifetime of a perfume is short and there is an increasing demand for biodegradable perfumes. So, what does the future hold? Perhaps pro-fragrances that slowly release fragrances, an increased use of pheromones in perfumes, or advances in computing power may enable computer-aided fragrance design. Maybe perfumes will not only make us smell better, but improve our physical and emotional wellbeing?

Skip to 2 minutes and 5 secondsWhatever direction, the ultimate aim is the rational design of fragrance molecules - the perfume industry is valued at over £20 billion per year, so the ability to predict how a molecule's structure will affect its odour, is not to be sniffed at.

Chemical attraction and organic compounds

Although chemists come from different countries and speak different languages, they all understand chemical formulae. For example, in methane – which has the chemical formula CH4 – it is important to know that there are four hydrogen atoms and a carbon atom, and that carbon forms bonds to each of the hydrogen atoms. (Methane is the main component of natural gas, a fossil fuel commonly used for heating and cooking.)

Many of you may have not done Chemistry for a while, so following this is a recap about drawing chemical structures, in particular, organic compounds which is the subject of this course. You will see that there are different ways for showing chemical structures, each providing different levels of detail.

This course focuses on organic chemistry, which studies over 16 million compounds that involve carbon. We call these organic compounds. Organic compounds include natural products, such as sugars and alkaloids, which are central for life, and synthetic (or man‐made) compounds, including plastics, dyes, perfumes and medicines that are important to our everyday lives. Familiar examples include:

Acetone – a good solvent with a range of medical and cosmetic applications, including use as nail polish remover.

Aspirin – one of the cheapest and most popular pain-relieving agents on the market (in 1950 it was entered in the Guinness World Records for being the most frequently sold painkiller).

Caffeine – the most consumed psychoactive substance in the world. A psychoactive substance is one that acts on the central nervous system and brain, affecting our perception, mood and behaviour. Many people associate psychoactive with illicit drugs like marijuana, but a number of psychoactive substances are legal, including alcohol and tobacco.

Cellulose – the world’s most abundant organic compound. It is made by linking together lots of glucose units and it gives form and strength to cell walls. Cellulose is often added to diet foods because we cannot digest it (so it has no calories), but it creates a sensation of fullness in the stomach.

Dexamethasone – this low cost steroid became the first life-saving treatment in the Covid-19 pandemic. The Recovery trial (the biggest randomised controlled study of drugs against Covid-19 in the world) showed this compound was responsible for the survival of one in eight of the sickest patients.

Indigo – originally extracted from plants, today indigo is synthetically produced on an industrial scale mainly for use as a dye; each year, it is used to colour over one billion pairs of blue jeans around the world.

Morphine – a very powerful painkiller used during medical procedures and for acute and chronic pain management. It can be habit-forming, and people can develop a dependence on it. (You may have read that John Pemberton, the inventor of Coca-Cola, sought a cure for morphine addiction by experimenting with coca and coca wines.)

Saccharin – an artificial sweetener discovered accidentally in the lab, in 1879, which is about 300–400 times as sweet as sucrose or table sugar. Interestingly, although we find it sweet, bees or butterflies, which usually crave the sweetness of nectar, do not treat it as a desirable substance.

Testosterone – the only substance scientifically proven to act as an aphrodisiac. It works by increasing reactivity of the sympathetic nervous system, which plays a role in the regulation of human sexual responses.

(For the structures of some of these compounds, see the photomontage in the downloads section below.)

Before we start it is worth explaining the relationship between natural and synthetic compounds. If a compound synthesised in the laboratory has the same molecular structure as a natural product, then they are exactly the same compound. The vitamin C extracted from a lemon has the same structure as vitamin C synthesised in the laboratory - as they have identical structures they will have the same effect in the body (one can substitute the other). Also, just because something is natural, it does not mean it is good for us. Some of the most deadly poisons are found in plants – from atropine and scopolamine in deadly nightshade to ricin in a castor bean.

It is also worth mentioning the term ‘chemical-free’. Do you know a product that is 100% chemical-free? If so, you could win £1 million from the Royal Society of Chemistry. Unfortunately, no one could win this prize as everything we eat, drink, drive, play with and live in is made of chemicals - both natural and synthetic chemicals are essential for life! Take a look at the clip below which mentions a recent TV advert for a steam cleaner proudly proclaimed it is ‘100% chemical free’ as it uses ‘nothing but tap water’ - but, water is a chemical!

This is an additional video, hosted on YouTube.

A colleague forwarded me a photo of a cranberry and raspberry drink, with the message: ‘It’s NOT made with weird chemicals. There’s NO potassium sorbate, NO aspartame and NO sodium benzoate. NONE whatsoever. It’s simply made with natural fruit extracts, fruit juices and still water. Refreshing and delicious.’ This begs the question, what is a ‘weird’ chemical? (My dictionary defines weird as something supernatural, unearthly.) Also, among many other chemicals (including ellagitannins, anthocyanins and flavonoids), berries contain benzoic acid, and sodium benzoate occurs naturally in very low levels in berries, including, yes, in cranberries and raspberries!

Have you come across any misleading adverts for so-called ‘safer, chemical-free products’?


In the news

On 7 June, you may have heard about an interview with Attorney General William Barr regarding the clearing of protestors in Washington, D.C. In the interview, with CBS News’ Margaret Brennan, Barr denied that police used tear gas on protestors at the park. Brennan says, “There were chemical irritants, the park police has [sic] said,” and Barr interrupted, “No, there were not chemical irritants. Pepper spray is not a chemical irritant. It’s not chemical.” Let’s be clear, pepper spray is a chemical. The active ingredient is capsaicin, the chemical that gives chilli peppers their heat. It contains 18 carbon atoms, 27 hydrogen atoms, an atom of nitrogen and three oxygen atoms per molecule (C18H27NO3)!

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This video is from the free online course:

Exploring Everyday Chemistry

University of York