When one understand the two nucleophilic substitution reactions, SN1 and SN2, it is the feasibility of the formation of the carbocation that determines whether the nucleophilic substitution reaction occurs by the former means or by the latter method.
However, the best way to determine the mechanism is to perform a kinetics experiment; by finding out how the rate of reaction is affected by the concentration of the reaction; we can conclude whether it is SN1 or SN2. Hence, this entry aims to compare the two different mechanisms.
In SN1, we expect that the rate of the reaction to be affect by the concentration of the alkyl halide only. In addition, if the initial alkyl halide is chiral, the product produced will be a racemic mixture. This is because in this mechanism, the carbocation formed is planar. Hence, the attacking nucleophile can attack the carbocation on either side of the plane, in equal probability. Hence, resulting in a racemic mixture to be formed.
In SN2, the rate of reaction is affected by both the concentration of the alkyl halide and the concentration of the nucleophile. From the mechanism of the reaction, if the initial alkyl halide chiral, the product formed will also be chiral and no racemic mixture is formed.
In addition, when we compare the energy profile diagrams of SN1 and SN2, we can see that the former has two peaks, hence two transition states and 1 intermediate, while the former has just one peak, hence 1 transition state and no intermediate formed.
Therefore, the energy profile diagram reinforce that the SN1 is a two-steps reaction while the SN2 is a single step reaction.
In conclusion, these post highlights three differences the two mechanisms possess. Do you think there are any further differences?
-- -- -- -- --However, the best way to determine the mechanism is to perform a kinetics experiment; by finding out how the rate of reaction is affected by the concentration of the reaction; we can conclude whether it is SN1 or SN2. Hence, this entry aims to compare the two different mechanisms.
In SN1, we expect that the rate of the reaction to be affect by the concentration of the alkyl halide only. In addition, if the initial alkyl halide is chiral, the product produced will be a racemic mixture. This is because in this mechanism, the carbocation formed is planar. Hence, the attacking nucleophile can attack the carbocation on either side of the plane, in equal probability. Hence, resulting in a racemic mixture to be formed.
In SN2, the rate of reaction is affected by both the concentration of the alkyl halide and the concentration of the nucleophile. From the mechanism of the reaction, if the initial alkyl halide chiral, the product formed will also be chiral and no racemic mixture is formed.
In addition, when we compare the energy profile diagrams of SN1 and SN2, we can see that the former has two peaks, hence two transition states and 1 intermediate, while the former has just one peak, hence 1 transition state and no intermediate formed.
Therefore, the energy profile diagram reinforce that the SN1 is a two-steps reaction while the SN2 is a single step reaction.
In conclusion, these post highlights three differences the two mechanisms possess. Do you think there are any further differences?
Article written by Kwok YL 2009.
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