Charles Gerhardt, Précis de chimie organique (Summary of organic chemistry), vol. 1 (Paris, France: Fortin et Masson, 1844), page 29. From page 29: "En désignant, par conséquent, les éléments combustibles par R, sans tenir comptes des proportions atomiques de carbone et d'hydrogène, on peut exprimer d'une manière générale: Par R. — Les hydrogènes carbonés." (Consequently, by designating combustible components by R, without considering the atomic proportions of carbon and hydrogen, one can express in a general way: By R — hydrocarbons.)
Stanislao Cannizzaro (1858) "Sunto di un corso di filosofia chimica, fatto nella R. Universita di Genova" (Sketch of a course of chemical philosophy, offered at the Royal University of Genoa), Il Nouvo Cimento (The New Experiment), 7 : 321–366. From page 355: " … X indica tutto ciò che vi è nella molecola, oltre l'idrogeno metallico … " ( … X stands for all that is in the molecule, apart from metallic hydrogen … ).
doi.org
dx.doi.org
PAC, 1996, 68, 2287. Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure and Applied Chemistry, 1996, s. 2287–2311. Dostupné online. DOI: 10.1351/pac199668122287.
Why Is "R" Used To Symbolize Hydrocarbon Substituents?. Journal of Chemical Education, 2010, s. 360–361. DOI: 10.1021/ed800139p.
Cheminformatics Analysis of Organic Substituents: Identification of the Most Common Substituents, Calculation of Substituent Properties, and Automatic Identification of Drug-like Bioisosteric Groups. Journal of Chemical Information and Modeling, 2003, s. 374–380. DOI: 10.1021/ci0255782. PMID 12653499.
iupac.org
goldbook.iupac.org
PAC, 1996, 68, 2287. Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure and Applied Chemistry, 1996, s. 2287–2311. Dostupné online. DOI: 10.1351/pac199668122287.
nih.gov
ncbi.nlm.nih.gov
Cheminformatics Analysis of Organic Substituents: Identification of the Most Common Substituents, Calculation of Substituent Properties, and Automatic Identification of Drug-like Bioisosteric Groups. Journal of Chemical Information and Modeling, 2003, s. 374–380. DOI: 10.1021/ci0255782. PMID 12653499.
uc.edu
che.uc.edu
William B. Jensen (2010) "Ask the Historian: Why is R Used for Hydrocarbon Substituents?," Journal of Chemical Education, 87: 360–361. Available at: University of Cincinnati.
worldcat.org
HRNČIAR, Pavol. Organická chémia : Celoštát. vysokošk. učeb. pre prírodoved. a ped. fak. vys. šk.. Bratislava : Slov. ped. nakl, 1990. (3. preprac. vyd.) Dostupné online.ISBN 80-08-00028-7.