Practice your electron-pushing skills by drawing a mechanism for the following Sₙ2 reactions.
(b)
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Identify the nucleophile and the electrophile in the reaction. The nucleophile is the species that donates an electron pair, while the electrophile is the species that accepts an electron pair.
Recognize that an Sₙ2 reaction involves a single concerted step where the nucleophile attacks the electrophile from the opposite side of the leaving group, leading to an inversion of configuration at the carbon center.
Draw the nucleophile approaching the electrophilic carbon atom from the side opposite to the leaving group. Use a curved arrow to show the movement of the electron pair from the nucleophile to the electrophilic carbon.
Simultaneously, draw another curved arrow from the bond between the electrophilic carbon and the leaving group to the leaving group itself, indicating that the leaving group is departing with the electron pair.
Ensure that the final product shows the nucleophile bonded to the carbon atom, with the leaving group completely detached, and note the inversion of stereochemistry at the carbon center if applicable.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sₙ2 Mechanism
The Sₙ2 (substitution nucleophilic bimolecular) mechanism involves a nucleophile attacking an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction occurs in a single concerted step, meaning that bond formation and bond breaking happen simultaneously. The reaction rate depends on the concentration of both the nucleophile and the substrate, making it bimolecular.
Nucleophiles are species that donate an electron pair to form a chemical bond in a reaction. They are typically negatively charged or neutral molecules with lone pairs of electrons, which allow them to attack positively polarized atoms in electrophiles. Understanding the strength and reactivity of different nucleophiles is crucial for predicting the outcome of Sₙ2 reactions.
Leaving groups are atoms or groups that can depart from the substrate during a chemical reaction, taking with them the electrons from the bond they shared with the substrate. A good leaving group is typically stable after departure, such as halides or sulfonate groups. The ability of a leaving group to stabilize its negative charge significantly influences the rate and feasibility of Sₙ2 reactions.