Cloves and Hops

Caryophyllene (7.137) is the commonest member of the family and is found in a wide variety of plants from herbs such as basil and spices such 

As mentioned in Chapter 2, these molecules all suffer a high level of strain in the rings. Medium sized rings experience steric strain and the introduction of trans double bonds increases this significantly. This stored energy has dramatic effects on the chemistry of the caryophyllenes and humulenes as we shall see. 

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Frost was not thinking of perfume when he wrote this line in his poem Stopping by woods on a snowy evening . However, his words do apply very well to the role of woody notes in a fragrance. The woods sit down under the heart of a composition and give it richness and depth. In this chapter, the term wood is used in the perfumistic rather than the botanical sense since it covers not only wood (pine) but also roots (vetiver), leaves (patchouli) and flowers (cloves and hops). 

The major terpenoid components of cloves and hops are remarkable in that they contain highly strained medium sized rings. Four of the most important members of the family are shown in Figure 7.29. Of these, the most important are P-caryophyllene (7.137) and a-humulene (7.139). These are the most frequently encountered in essential oils and are often referred to simply as caryophyllene and humulene, respectively. For convenience, these shorter names will be used in this book. For example, a-humulene (7.139) has been found in hundreds of essential oils whereas there are reports of P-humulene (7.140) in only a few. Almost invariably, several members of the family will be found together in oils. For example, all oils which have been found to contain humulene (7.139) also contain caryophyllene (7.137) and isocaryophyllene (7.138). 

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