Chapter 3: Perfumes, Volatile Plant Scents

Chapter 3 focuses on the composition of plant scents, the “perfumes”: they are mixtures of nonpolar, volatile oils composed of many different organic compounds. Plant scents describe a first group of secondary plant metabolites. Some of the volatile compounds act as attractants for animals, others have defensive functions. This chapter describes attractive smells of flowers and fruits. Many pleasant fragrances (from a human perspective) are composed of terpenes or isoprenoids, with molecules that have characteristic five-carbon building blocks called isoprene units. Other attractive smells consist of low-molecular-weight aromatic compounds, “aromatic” meaning here “with a benzene ring”. Functional groups attached to the carbon backbone of the molecules can further characterize or enhance smells. Attractive scents of various ripe fruits are provided by esters. On the other hand, amines and sulfurous compounds can produce foul odors that remind us of rotten meat or decaying fish but are highly attractive to flies and beetles. Gas chromatography, often combined with mass spectrometry, is a highly sensitive technique used to analyze the complex compositions of plant scents.