Russell Cox Chem (@russellcoxchem.bsky.social)

Limonene in Citrus: A String of Unchecked Literature Citings? In organic chemistry textbooks (S)-(−)-limonene, (−)-limonene or l-limonene, is often given credit for the smell of lemons, while the R-analogue, (+)-limonene or d-limonene, is credited with that of oranges. Results from two odor tests revealed that few persons in the test associated (R)-(+)-limonene with oranges and (S)-(−)-limonene with lemons, when these compounds were of analytical grade. Quality and composition of standard compounds and mixtures used in these olfactory tests were corroborated by gas chromatographic analyses. The statement of (R)-(+)-limonene being responsible for orange odor and (S)-(−)-limonene for the lemon odor apparently stems from an often quoted article from 1971. This investigation was a lesson for both our students and us. Textbooks in organic chemistry that still promote (R)-(+)- and (S)-(−)-limonene as, respectively, the “orange” and “lemon” smell ingredient should be corrected. https://pubs.acs.org/doi/10.1021/acs.jchemed.1c00363