How will the rate of each of the following SN 2 reactions change if it is carried out in a more

step 1 In question number 26, how will the rate of each of the following SN2 reactions change if it is

How will the rate of each of the following SN 2 reactions...

How will the rate of each of the following $\mathrm{S}_{\mathrm{N}} 2$ reactions change if it is carried out in a more polar solvent? a. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{HO}^{-} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{Br}^{-}$ b. c. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I}+\mathrm{NH}_{3} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2}+\mathrm{NH}_{3} \mathrm{I}^{-}$

How will the rate of each of the following $\mathrm{S}_{\mathrm{N}} 2$ reactions change if it is carried out in a more polar solvent?
a. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}+\mathrm{HO}^{-} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{Br}^{-}$
b.
c. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I}+\mathrm{NH}_{3} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2}+\mathrm{NH}_{3} \mathrm{I}^{-}$

Key Concepts

Transition State Stabilization

In the S_N2 reaction, the transition state is highly charged and polar because bonds are partially broken and formed simultaneously. More polar solvents can better stabilize this high-energy state by solvating the charge, which can lower the activation energy and potentially increase the reaction rate. The overall effect of a polar solvent depends on whether this stabilization outweighs any decrease in nucleophilicity due to solvation.

Nucleophile Solvation

Nucleophile solvation refers to the interaction between solvent molecules and the nucleophile. In polar protic solvents, small, charged nucleophiles become surrounded by solvent molecules, which hampers their ability to attack the substrate effectively. In contrast, less solvated nucleophiles in polar aprotic solvents tend to be more reactive in S_N2 reactions since they are freer to engage in the necessary backside attack.

S_N2 Reaction Mechanism

The S_N2 mechanism is a one?step, bimolecular nucleophilic substitution where the nucleophile attacks the electrophilic carbon from the backside, leading to a concerted process in which bond-forming and bond-breaking occur simultaneously. The overall reaction rate depends on both the substrate and the nucleophile, making it sensitive to changes in the reaction environment.

Solvent Effects on Reaction Rates

The polarity of the solvent can have a significant influence on the S_N2 reaction rate. Highly polar solvents stabilize charged species, including the transition state, by dispersing charge. However, in polar protic solvents, anionic nucleophiles are strongly solvated, which reduces their reactivity. This dual role means that solvent choice can either accelerate or decelerate the reaction, depending on the balance between transition state stabilization and nucleophile solvation.

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