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Pre-reaction complexes for reactions listed in Scheme 2. In (a) the absence of hydrogen bonding positions F− favorable for fluorination, whereas in (b) hydrogen bonding with -NHR moves F− far off the reaction center. M06-2X/6-311G ** method for C, H, O, N, F, S atoms, LANL2DZ basis set with relevant effective core potential for alkali metal elements (I, Br, Cs), using Gaussian 09 set of programs.
