Comparing Two Types Of Nucleophilic Na

There are two types of nucleophilic substitution: SN2 and SN1. The SN2 reaction mechanism is concerted meaning it involves only one step where the bonds of the leaving group and nucleophile are being formed and broken simultaneously1. The rate for this mechanism is dependent on both the concentration of the nucleophile and alkyl halide. The following figure displays the general mechanism for a SN2 reaction. The SN1 reaction mechanism is stepwise meaning that the leaving group departs first to create a carbocation intermediate, which later bonds with the nucleophile. The rate of this reaction is just dependent on the concentration of the alkyl halide.1 The following figure displays the general mechanism for a SN2 reaction. When comparing these two mechanisms’ rates, it is important to consider these factors: the structure of the alkyl halide, the leaving group, and the solvent.

Since SN2 reactions require the nucleophile attacking the alkyl halide at the backside, the reaction can only happen if the empty orbital is accessible2. This means that if there are many groups close to the leaving group, then the reaction will be slower because the nucleophile will have a harder time accessing the alkyl halide. The less steric hindrance the alkyl halide has, the faster the reaction because there is less activation energy needed to overcome the steric hindrance2. For this reason, the rate of reaction is fastest on a primary carbon rather than a tertiary carbon because there is less steric hindrance on the primary carbon compared to the tertiary carbon. For this lab procedure, four alkyl halides are compared, and their structures are displayed down in the figure down