A student ran two separate substitution reactions, reaction A and reaction B, in lab that utilized an alkyl halide and a nucleophile. However, he did not know if the reactions proceeded through an SN1 or SN2 mechanism. To determine the mechanism for both reactions, the student increased the concentration of the nucleophile in reactions A and B. The rate of reaction for reaction A increased. The rate of reaction for reaction B remained the same.
(a) Which reaction is the SN1 reaction?
(b) Which reaction is the SN2 reaction?
(c) Explain both choices.