Predicting the increase in electron affinity of phenoxy upon fluorination

Abstract

The site-specific fluorination of organic compounds can alter their electron affinity, EA, which in turn can be used to control their reactivity, physical properties, or binding affinities. Using anion photoelectron spectroscopy, we show that for the multiply fluorinated phenoxy radical, the change in EA is predominantly additive per fluorination and can be predicted by the simple formula: ΔEA = ${\sum }_i$ΔEA_i − ΔEA_C, where the numeric index i indicates the positions of fluorination. A small cooperative effect, ΔEA_C, destabilizes the anion, but this only accounts for 11 % of the total ΔEA, in the extreme case of pentafluorophenolate. Our experimental results are consistent with those calculated using density functional theory, demonstrating the suitability of electronic structure calculations in the prediction of fluorination effects, for practical use in the synthetic design of organofluorines.