Here is a thought-provoking recent study from Professor G. K. Surya Prakash, my PhD mentor. The work, done in collaboration with Professor Herbert Mayr, reports a surprising outlier in what might otherwise be an intuitively clear nucleophilicity trend. It turns out that fluorine-containing carbanions can be up to 35 times more nucleophilic than their hydrogen congeners. While the authors do not suggest a simple explanation for the observed effect, one might hazard to guess that a heteroatom in place of hydrogen would increase the pyramidalization of the proximal anionic carbon centre. This increase, induced by the electron-withdrawing heteroatom, could lead to augmented nucleophilicity. While this is admittedly sound, the chlorinated analog does not follow the trend, throwing a wrench into what we all crave – a simple explanation. Fluorine is never boring and this Angewandte report provides yet another illustration.
http://onlinelibrary.wiley.com/doi/10.1002/ange.201605616/full