Brande, William Thomas (1848). A Manual of Chemistry, Vol II (6 ed.). London: John W. Parker. p. 1344. Retrieved 8 November 2023.
doi.org
Pfendt, L.; Dražić, B.; Popović, G.; Drakulić, B.; Vitnik, Ž; Juranić, I. (2003). "Determination of all pKa values of some di- and tri-carboxylic unsaturated and epoxy acids and their polylinear correlation with the carboxylic group atomic charges". Journal of Chemical Research. 2003: 247–248. doi:10.3184/030823403103173732.