Revealing the Positive Side of Fluorine

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Science  05 Apr 2013:
Vol. 340, Issue 6128, pp. 41-42
DOI: 10.1126/science.1236150

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Organofluorine compounds have found widespread applications in diverse areas such as polymers, liquid crystals, and agricultural and medicinal chemistry (1, 2). Partial or full fluorination provides distinctive physicochemical properties to an organic molecule that can be attributed to the special properties of the carbonfluorine (C-F) bond (3). Fluorine is the most electronegative (electron-attracting) element of the periodic table, so the C-F bond is highly polarized. The small size and high electronegativity of the F atom gives it a low polarizability. This property makes it difficult for fluorine's electron pairs to engage in hypervalent bonding, as other halogens can do, to form a fluoronium ion, a structure in which the fluorine is bonded to two carbon atoms with a (at least formal) positive charge at fluorine. However, on page 57 of this issue, Struble et al. (4) report strong evidence in support of precisely such a fluoronium ion.