For the following reaction, the cyanide nucleophile could reasonably substitute at either of two positions. one mechanism produces 4-cyanoheptane and dimethylsulfide. the competing mechanism produces 4-methylthioheptane and acetonitrile (ch_3cn). in practice, only one substitution is observed. choose the most likely mechanistic pathway for this reaction and draw both of the products. select whether it proceeds via an sn1 or sn2 mechanism.