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Terpenes are unsaturated hydrocarbons, formed by joining together units of 2-methylbuta-1,3-diene. This molecule is also known as isoprene.

These unsaturated C₅H₈ units can add together head to tail to form terpenes. Both long, straight chain molecules, or cyclic molecules can be formed.

After being oxidised within plants, terpenes are responsible for the flavours of many distinct spices such as ginger, cloves and cinnamon.