Here are the essential concepts you must grasp in order to answer the question correctly.
Sₙ2 Reaction Mechanism
The Sₙ2 (bimolecular nucleophilic substitution) reaction mechanism involves a single concerted step where a nucleophile attacks an electrophile, leading to the simultaneous displacement of a leaving group. This mechanism is characterized by a second-order reaction rate, meaning the rate depends on the concentration of both the nucleophile and the substrate. Sₙ2 reactions typically favor primary and some secondary haloalkanes due to steric accessibility.
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Steric Hindrance
Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In the context of Sₙ2 reactions, increased steric hindrance around the electrophilic carbon atom can slow down or inhibit the reaction. Therefore, primary haloalkanes, which have less steric hindrance, generally react faster than secondary or tertiary haloalkanes in Sₙ2 mechanisms.
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Leaving Group Ability
The ability of a leaving group to depart from a molecule is crucial in determining the rate of Sₙ2 reactions. Good leaving groups, such as iodide or bromide, stabilize the negative charge after leaving, facilitating the reaction. Conversely, poor leaving groups, like fluoride or hydroxide, hinder the reaction process. Thus, the choice of haloalkane with a better leaving group can significantly influence the speed of the Sₙ2 reaction.
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