Alkenes halogen-bond basicity

The first term, representing acid-"catalyzed" hydrolysis, is important in reactions of carboxylic acid esters but is relatively unimportant in loss of phosphate triesters and is totally absent for the halogenated alkanes and alkenes. Alkaline hydrolysis, the mechanism indicated by the third term in Equation (2), dominates degradation of pentachloroethane and 1,1,2,2-tetrachloroethane, even at pH 7. Carbon tetrachloride, TCA, 2,2-dichloropropane, and other "gem" haloalkanes hydrolyze only by the neutral mechanism (Fells and Molewyn-Hughes, 1958 Molewyn-Hughes, 1953). Monohaloalkanes show alkaline hydrolysis only in basic solutions as concentrated as 0.01-1.0 molar OH- (Mabey and Mill, 1978). In fact, the terms in Equation(2) can be even more complex both elimination and substitution pathways can operate, leading to different products, and a true unimolecular process can result from initial bond breaking in the reactant molecule. 

As a rule, in nucleophilic additions to halogenated alkenes, the nucleophile always becomes attached to that carbon of the double bond that has lower electron density. In this case, back-donation of electrons by fluorine is stronger in the difluoromethylene group, and nitrogen therefore attacks the difluoromethylene group while proton adds to the other carbon. Because of the basicity of the reaction mixture, hydrogen fluoride is eliminated, and an imide fluoride, 3-chloro-2,3-difluoro-l-phenyl-1-aza-propene is formed ... 

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