text: which of the following undergoes a substituteion reaction with sodium cyanide in dmso at the fastest rate? which of the following undergoes a substituteion reaction with sodium cyanide in dmso at the fastest rate?  a. ch3ch2f b.ch3ch2cl c.ch3ch2br d.ch3ch2i the answer is (d), ch3ch2i  in order of relative reactivity in terms or leaving groups, it goes:  f-   -   1 cl-  -   200 br-  -   10000 i-     -   30000  the weakest bases are the best leaving groups.