The Persistent Myth of Limonene's Smell

Abstract

The scent of the well-known monoterpene limonene is thoroughly investigated. Despite this, the scientific community does not reach consensus. In this Perspective article, a discussion is contributed by giving a simple overview of the olfactory system, as well as presenting the smell of well-known compounds and their odor threshold values in citrus oils, from which (R)-limonene is extracted. In particular, the composition of oils from orange and lemon peel and their association with the (R)- and (S)-enantiomers of limonene, respectively, are considered. Then, the controversy surrounding the odors of (R)- and (S)-limonene and the myth that has been spun from this are reported, particularly in the organic chemistry literature, before an argument for why this myth should be dismantled. Based on the chemical and physiological processes involved in the sense of smell, whether the odor attributed to a certain compound is from that compound and/or from derivatives produced by enzymes associated with the olfactory system is also briefly discussed.