(••) For each pair, choose the haloalkane that would react most quickly in an Sₙ2 reaction.


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Verified step by step guidance

1. Identify the structure of each haloalkane in the pair. Consider the type of carbon to which the halogen is attached (primary, secondary, or tertiary).
2. Recall that Sₙ2 reactions proceed most rapidly with primary haloalkanes due to less steric hindrance, which allows the nucleophile to attack more easily.
3. Evaluate the steric hindrance around the carbon atom bonded to the halogen in each haloalkane. Less steric hindrance means a faster Sₙ2 reaction.
4. Consider the leaving group ability. A better leaving group will facilitate a faster Sₙ2 reaction, but in this case, focus primarily on steric factors.
5. Compare the two haloalkanes based on the above criteria and determine which one is more likely to undergo the Sₙ2 reaction more quickly.

Key Concepts

Sₙ2 Reaction Mechanism

The Sₙ2 (substitution nucleophilic bimolecular) reaction is a type of nucleophilic substitution where the nucleophile attacks the electrophile simultaneously as the leaving group departs. This concerted mechanism results in the inversion of configuration at the carbon center. The rate of the Sₙ2 reaction depends on steric hindrance and the strength of the nucleophile, making it crucial to identify which haloalkane is less hindered for a faster reaction.

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, bulky groups around the carbon atom can impede the approach of the nucleophile, slowing down the reaction. Therefore, haloalkanes with less steric hindrance, such as primary haloalkanes, typically react more quickly than secondary or tertiary haloalkanes.

Leaving Group Ability

The ability of a leaving group to depart from a molecule is a critical factor in determining the rate of nucleophilic substitution reactions. Good leaving groups, such as iodide or bromide, stabilize the negative charge after leaving, facilitating the reaction. In contrast, poor leaving groups, like hydroxide or alkoxide, hinder the reaction. Understanding the nature of the leaving groups in the haloalkanes is essential for predicting which compound will react more quickly in an Sₙ2 reaction.