HC CHEMISTRY HC CHEMISTRY NATURES’ CHEMISTRY (E) Fragrances

HC HC (E) Fragrances Isoprene Unit CHEMISTRY HC CHEMISTRY (E) Fragrances Isoprene Unit After completing this lesson you should be able to : Terpenes are unsaturated compounds formed by joining together isoprene (2- methylbuta-1,3-diene) units. Terpenes can be oxidised within plants to produce some of the compounds responsible for the distinctive aroma of spices.

b) Terpenes Learning intention Learn about the chemistry and uses of terpenes, a key group of unsaturated molecules based upon isoprene.

Terpenes COPY The name ‘terpene’ is derived from the Greek word ‘terebinth’. Terebinth is a type of pine tree from which terpene-containing resins are obtained. Pistacia palaestina is a tree or shrub common in the Levant region (especially Palestine, Israel and Syria). It is called terebinth in English, a name also used for Pistacia terebinthus, a similar tree from the western Mediterranean Basin.

Terebinth In the book Voyage of the Dawn Treader, C. S. Lewis named one of the fictional islands "Terebinthia"; Lewis scholar Marvis. D. Hinten posits "Lewis, the renowned medieval scholar, naturally knew that terebint was Middle English for the tree used in the Middle Ages to produce turpentine." Katherine Paterson, the author of the 1977 novel Bridge to Terabithia noted she had probably unintentionally taken the name of her fictional world from C. S. Lewis, who had likely taken the name from the tree.

Terpenes to steroids Essential oils of many plants and flowers are obtained by distilling the plant with water. The water-insoluble oil that separates usually has an odor characteristic of the particular plant (rose oil, geranium oil and others). Compounds isolated from these oils contain multiples of five carbon atoms (that is, 5, 10, 15 and so on) and are called terpenes. They are synthesised in the plant from acetate by way of an important biochemical intermediate, isopentyl pyrophosphate. The five-carbon chain and a one-carbon branch at C-2 is called an isoprene unit.

What are terpenes? Natural organic compounds. COPY What are terpenes? Natural organic compounds. Components of a variety of fruit and floral flavours and aromas. Used in perfumes, essential oils and medicines.

Essential oils contain terpenes COPY 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.

Spices contain terpenes COPY 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.

Terpenes are unsaturated COPY Terpenes are unsaturated Terpenes are unsaturated compounds. All terpenes are built up from units of isoprene.

COPY Isoprene Isoprene is the common name for 2-methylbuta-1,3-diene

COPY Isoprene One isoprene unit contains five carbon atoms

Building terpenes from isoprene COPY Building terpenes from isoprene Isoprene units can be linked: head to tail to form linear terpenes in rings to form cyclic terpenes.

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

Limonene – a cyclic terpene COPY Limonene – a cyclic terpene

Menthol – a cyclic terpenoid COPY Menthol – a cyclic terpenoid This terpene has been oxidised to a terpenoid

Absinthe – a cyclic terpenoid COPY Absinthe – a cyclic terpenoid This terpene has been oxidised to a terpenoid Thujone is a ketone and a monoterpene Though it is best known as a chemical compound in the spirit absinthe, absinthe contains only small quantities of thujone, so thujone is unlikely to be responsible for absinthe's alleged psychedelic effects. Thujone, as a component of several essential oils, is also used in perfumery. Thujone podcast

Camphor – a cyclic terpenoid COPY Camphor – a cyclic terpenoid

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

β-carotene – a linear terpene COPY 8 isoprene units 40 carbon atoms

Squalene 6 isoprene units 30 carbon atoms

Questions Which unit makes up every terpene? COPY Questions 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?

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

COPY 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.