Practice your electron-pushing skills by drawing a mechanism for the following S_N1 reactions.
(c)

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Identify the substrate in the reaction. For an Sₙ1 reaction, the substrate is typically a tertiary alkyl halide or a secondary alkyl halide, as these stabilize the carbocation intermediate formed during the reaction.

Determine the leaving group. In an Sₙ1 reaction, the leaving group departs first, forming a carbocation intermediate. Ensure the leaving group is a good one, such as a halide ion (e.g., Cl⁻, Br⁻, or I⁻).

Draw the first step of the mechanism: the heterolytic cleavage of the bond between the carbon atom and the leaving group. Use curved arrows to show the movement of electrons from the bond to the leaving group, resulting in the formation of a carbocation and the leaving group as an anion.

Analyze the stability of the carbocation intermediate. If the carbocation can undergo rearrangement (e.g., hydride shift or alkyl shift) to form a more stable carbocation, draw the rearrangement step using curved arrows to show the movement of electrons.

Draw the nucleophilic attack step. The nucleophile (e.g., water, alcohol, or another nucleophile present in the reaction) will attack the carbocation, forming a new bond. Use curved arrows to show the movement of electrons from the nucleophile to the carbocation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Sₙ1 Mechanism

The Sₙ1 (substitution nucleophilic unimolecular) mechanism involves a two-step process where the leaving group departs first, forming a carbocation intermediate. This is followed by the nucleophile attacking the carbocation. The rate of the reaction depends only on the concentration of the substrate, making it unimolecular. Understanding this mechanism is crucial for predicting the behavior of substrates in nucleophilic substitution reactions.

Carbocation Stability

Carbocations are positively charged species that play a key role in Sₙ1 reactions. Their stability is influenced by factors such as the degree of substitution (primary, secondary, tertiary) and resonance. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups. Recognizing the stability of carbocations helps in predicting the feasibility and rate of Sₙ1 reactions.

Nucleophiles

Nucleophiles are species that donate an electron pair to form a chemical bond in a reaction. In Sₙ1 reactions, the nucleophile attacks the carbocation after the leaving group has departed. The strength and nature of the nucleophile can significantly affect the reaction rate and outcome. Common nucleophiles include water, alcohols, and halides, and understanding their reactivity is essential for drawing accurate reaction mechanisms.

Practice your electron-pushing skills by drawing a mechanism for the following SN1 reactions.(c)