Perfluoro-t-butyl iodide (Ⅰ) was synthesized by the application of the method of Krespan.It was found that this method can be extended by the use of bromine in place of iodine for the synthesis of the corresponding bromide (Ⅱ).The first step in the reactions of the iodide (Ⅰ) with diethyl amine and ethanolic potassium hydroxide is shown to involve an S_N2-like attack on the iodine atom by the nucleophile.The products of the above reactions were identical with those from the reactions between perfluoro-isobutene and the corresponding nucleophiles.Ultraviolet solvent shifts,δ(H-B),were determined for CF₃)₃CI,(CF₃)₂CFI,and CF₃CF₂CF₂I.The δ(H-B) values provide evidence for an electron-withdrawing inductive order for perfluoro alkyl groups such as:(CF₃)₃C->(CF₃)₂CF->CF₃CF₂->CF₃-.Arguments for the above order and against the generally accepted views are presented.