α-Stabilization of carbanions:: Fluorine is more effective than the heavier halogens

Ready steady go! The basicity of the carbanions CH2X- decreases continuously in the series X=F, Cl, Br, I. However, contrary to the common assumption, this occurs not because of the increasing α-stabilization of CH2X-: F stabilizes CH 2X more effectively than Cl, Br, and I (see picture). This apparent contradiction results from the usually ignored stabilization of the corresponding acids CH3X by X. (Graph Presented). © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.