(••) Identify whether each of the following reactions proceed by an S_N1 ,S_N2 , E1, or E2 mechanism.


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Verified step by step guidance

1. insert step 1> Identify the substrate structure in the reaction. Consider whether it is primary, secondary, or tertiary, as this will influence the mechanism.
2. insert step 2> Examine the nature of the leaving group. A good leaving group is necessary for both substitution and elimination reactions.
3. insert step 3> Consider the strength and type of the nucleophile or base. Strong nucleophiles favor S_N2 reactions, while strong bases favor E2 reactions.
4. insert step 4> Analyze the reaction conditions, such as solvent and temperature. Polar protic solvents favor S_N1 and E1 mechanisms, while polar aprotic solvents favor S_N2.
5. insert step 5> Determine the mechanism based on the combination of substrate, leaving group, nucleophile/base, and reaction conditions.

Key Concepts

S_N1 Mechanism

The S_N1 mechanism involves a two-step process where the leaving group departs first, forming a carbocation intermediate. This mechanism is favored in tertiary substrates due to their stability and occurs in polar protic solvents. The rate of reaction depends only on the concentration of the substrate, making it unimolecular.

S_N2 Mechanism

The S_N2 mechanism is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs. This mechanism is characterized by a concerted reaction and is favored in primary substrates due to steric accessibility. The rate of reaction depends on both the substrate and nucleophile concentrations, making it bimolecular.

E1 and E2 Mechanisms

E1 and E2 are elimination mechanisms. E1 involves a two-step process similar to S_N1, where a carbocation is formed before the elimination of a proton, typically favored in tertiary substrates. E2 is a one-step concerted reaction where a base abstracts a proton while the leaving group departs, favored in strong bases and often seen with primary substrates.