Question

Nucleophilicity of halides in sn2 reaction

Answer 1

The order of nucleophilicity of halide ions depends on the medium.
In polar aprotic solvents ( eg: DMF, DMSO) nucleophilicity is the same as basic character i.e. F- > Cl- > Br- > I-
In polar protic solvents ( eg; h2o,hcl) nucleophilicity is opposite of basic character.
SN2 reaction occurs in polar aprotic solvent of low polarity.Hence, nucleophilicity of halides in SN2 is F- > Cl-> Br-> I-.