Give examples of the four charge-types of SN 2 reactions, as...

Give examples of the four charge-types of $S_N 2$ reactions, as shown in the first line of Table 7-1. $$ \begin{aligned} & \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}+: \mathrm{O}_{\mathrm{H}}-\longrightarrow \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{O} \mathrm{H} \\ & \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}+: \mathrm{BH}_3 \longrightarrow \end{aligned} $$ a sulfonium cation Dimethyl sulfide (table cant copy)

Give examples of the four charge-types of $S_N 2$ reactions, as shown in the first line of Table 7-1.
$$
\begin{aligned}
& \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}+: \mathrm{O}_{\mathrm{H}}-\longrightarrow \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{O} \mathrm{H} \\
& \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}+: \mathrm{BH}_3 \longrightarrow
\end{aligned}
$$
a sulfonium cation
Dimethyl sulfide
(table cant copy)

Key Concepts

Charge?Type Combinations in SN2 Reactions

SN2 reactions can be classified based on the charges of the nucleophile and the substrate, resulting in four distinct charge?types. These include: an anionic nucleophile with a neutral substrate, a neutral nucleophile with a neutral substrate, an anionic nucleophile with a positively charged substrate, and a neutral nucleophile with a positively charged substrate. Each combination displays different reactivity profiles and transition state characteristics, and understanding these variations is crucial for predicting reaction outcomes.

Influence of Substrate Charge

The intrinsic charge of the substrate, which includes the electrophilic site and its attached leaving group, can also significantly impact SN2 reactivity. A positively charged (electrophilic) substrate, such as a sulfonium ion, is more susceptible to nucleophilic attack because the positive charge increases the electrophilicity of the reaction center. Conversely, a neutral substrate may require a stronger nucleophile to effect the substitution.

Influence of Nucleophile Charge

The charge on the nucleophile plays a key role in its reactivity. Anionic nucleophiles, being more electron?rich, are typically more reactive than their neutral counterparts, allowing them to attack electrophilic centers more readily, whereas neutral nucleophiles require a more electrophilic substrate to achieve the same reaction rate.

SN2 Reaction Mechanism

SN2 (bimolecular nucleophilic substitution) is a one?step reaction mechanism in which a nucleophile attacks an electrophilic carbon at the same time as the leaving group departs. The reaction proceeds via a transition state in which bonds are partially broken and partially formed. The overall reaction rate depends on both the nucleophile and the substrate concentrations.

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