Aryl halides have a sp²-hybridized carbon in the C—X bond, which, with a greater s-character, holds the electron pair more tightly than the sp³-hybridized carbon in haloalkanes. The resulting shorter C—X bond in aryl halides makes their nucleophilic substitution reactions less reactive.
How does the difference in hybridization affect the reactivity of aryl halides in nucleophilic substitution reactions?
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Aryl halides, often derived from benzene rings, typically undergo nucleophilic aromatic substitution (SNAr) reactions. The reactivity of aryl halides is influenced by the hybridization state of the carbon involved in the substitution. Aryl halides exhibit sp² hybridization, which restricts the nucleophilic attack to the ortho and para positions due to resonance stabilization. The π electrons delocalized across the ring hinder nucleophile approach at the meta position. Additionally, the electron density on the carbon atom in aryl halides is lower than in sp³ hybridized alkyl halides, reducing the susceptibility to nucleophilic attack. These factors contribute to the distinctive reactivity of aryl halides in nucleophilic substitution reactions.