1. Fragrances
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Fragrances
Essential oils are concentrated extracts of the volatile, non-water soluble aroma compounds from plants
They are widely used in perfumes, cosmetic products, cleaning products and as flavourings in foods.
Essential oils are mixtures of organic compounds.
Terpenes are unsaturated compounds formed by joining together isoprene (2-methylbuta-1,3-diene) units
They are components in a wide variety of fruit and floral flavours and aromas.

3. Essential Oils
Essential oils are the concentrated extracts of volatile, non-water-soluble aroma compounds from plants.
Essential oils are widely used in perfumes, cosmetic products, cleaning products and as flavourings in foods.
Essential oils are mixtures of organic compounds.
Terpenes are the key components in most essential oils.

4. Modern uses Cosmetics Cleaning Flavours Dentistry Essential oils
Adhesives
Perfumes
Insect
repellents
Medical

5. Steam Distillation
Steam distillation is one of the methods used to extract essential oils from plants.
Steam passes over the plant and extracts the essential oil.
The mixture evaporates and passes into the condenser.
The essential oil vapour is chilled and collected

6. Terpenes
Terpenes are components of a wide variety of fruit and floral flavours and aromas.
Terpene derivatives are responsible for the distinctive aroma of spices.
Terpenes in plants can be oxidised to produce the compounds responsible for the distinctive aroma of spices.

7. Essential oils contain terpenes
Lavender – used to relieve tension.
Ylang-ylang – used to treat anxiety.
Lemon oil – aids good circulation.
Essential oils often contain a mixture of terpenes.

8. Can you draw the full structural formula for Isoprene?
Terpenes
Terpenes are unsaturated compounds formed by joining together isoprene units.
Isoprene has the systematic name:
2-methylbuta-1,3-diene
The molecular formula C5H8.
Can you draw the full structural formula for Isoprene?

9. head to tail to form linear terpenes OR
Isoprene units can be linked together in two ways:
head to tail to form linear terpenes OR
in rings to form cyclic terpenes.

10. Myrcene – a linear terpene
Head
Tail
Head
Tail + 
Myrcene is a component of plants, including bay, ylang-ylang and thyme.

11. Limonene is a cyclic terpene found in citrus fruits
Limonene is a cyclic terpene found in citrus fruits. It is made of two isoprene units linked in a ring.

12. Β-carotene is a linear terpene found in carrots
Β-carotene is a linear terpene found in carrots. It is made from 8 isoprene units linked head to tail.
8 isoprene units
40 carbon atoms

13. Spices contain terpenes
Terpenes in plants can be oxidised to produce the compounds responsible for the distinctive aroma of spices.
Terpenes containing oxygen or other functional groups are known as ‘terpenoids’.
Common spices containing terpenes include cloves, cinnamon and ginger.

14. Menthol is a cyclic terpenoid – a terpene which has been oxidised
Menthol is a cyclic terpenoid – a terpene which has been oxidised. It is found in peppermint and has a distinctive aroma.
This terpene has been
oxidised to a terpenoid

15. Absinthe – a cyclic terpenoid
This terpene has been
oxidised to a terpenoid

16. Camphor – a cyclic terpenoid

17. a-Selinene – a cyclic terpene
3 isoprene units
15 carbon atoms

18. Which unit makes up every terpene?
How many carbons are there in an isoprene unit?
What is the systematic name for isoprene?
What is an oxidised terpene known as?
Isoprene unit
Five
2-methylbuta-1,3-diene
Terpenoid

19. Summary
Terpenes are unsaturated compounds formed by joining together isoprene units.
Terpenes are components in a wide variety of fruit and floral flavours and aromas.
Terpenes can be oxidised within plants to produce the compounds responsible for the distinctive aroma of spices.

20. Two typical compounds that are present in many perfumes are shown.
(a) Why does geraniol evaporate more slowly than limonene? (1)
(b) The structure of one of the first synthetic scents used in perfume is shown below.
(i) Name the family of carbonyl compounds to which this synthetic scent belongs. (1)
(ii) Complete the structure below to show the product formed when this scent is oxidised. (1)
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21. (c) Traces of a liquid were discovered in a bottle believed to contain perfume belonging to Queen Hatshepsut, ruler of Egypt over 3500 years ago. Perfumes were made by dissolving plant extracts containing pleasant smelling terpenes and esters in an edible oil. A little ethanol and water may also have been added. Using your knowledge of chemistry, comment on the possible smell(s) when such a bottle is opened after being stored for thousands of years. (3)
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22. Skin Care
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Skin Care
Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight.
Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken.
This is the process responsible for sunburn and also contributes to aging of the skin.
Sun-block products prevent UV light reaching the skin.
When UV light breaks bonds, free radicals are formed.
Free radicals have unpaired electrons and, as a result, are highly reactive.
Free radical chain reactions include the following steps: initiation, propagation and termination.
Many cosmetic products contain free radical scavengers; molecules which can react with free radicals to form stable molecules and prevent chain reactions.
Free radical scavengers are also added to food products and to plastics.

24. Skin Care Products: Effect of Ultraviolet Light
Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight.
Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken. This is the process responsible for sunburn and also contributes to aging of the skin.
Sun-block products prevent UV light reaching the skin.

25. Free Radical Reactions
When UV light breaks bonds free radicals are formed.
Free radicals have unpaired electrons and, as a result, are highly reactive.
Free radical chain reactions include the following steps: initiation, propagation and termination.

26. Initiation
U.V. light provides the energy for the homolytic fission of a halogen into reactive halogen atoms or free radicals (atoms with an unpaired electron).
Cl2(g)  Cl.(g) Cl(g)

27. The product of this reaction is known as a hydrogen radical.
Propagation
In this stage, free radicals collide with other species but the number of free radicals is maintained (hence the term propagation).
H2(g) + .Cl  H.(g) + HCl(g)
The product of this reaction is known as a hydrogen radical.
H.(g) + Cl2(g)  HCl(g) + Cl. (g)
These reactions continue until reactants are used up, or until free radicals are used up by collision with each other.  
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28. Termination
In this stage, free radicals are used up by collision with each other.
H.(g) + .Cl(g)  HCl(g)
H.(g) + .H(g)  H2(g)
Cl.(g) + .Cl(g)  Cl2(g)

29. Free Radical Scavengers
Many cosmetic products contain free radical scavengers. These are molecules which can react with free radicals to form stable molecules and prevent chain reactions.
Melatonin and Vitamin E are examples of natural free radical scavengers.
Free radical scavengers are also added to food products and to plastics (antioxidants).