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Unformatted text preview: 3 o alkyl halides best substrates in S N 1, then 2 o ... but never 1 o or methyl Any substrate that can form a stable carbocation can react via S N 1 mechanism: Br allylic cation stabilized by resonance allylic bromide Br benzylic cation stabilized by resonance H 3 C CH 3 H 3 C Br F 3 C CF 3 F 3 C Br H 3 C CH 3 CH 3 + Br F 3 C CF 3 CF 3 + Br Which of these carbocations forms faster? K 1 K 2 A B Carbocation A is stabilized by the inductive effect of electron-releasing methyl groups and by hyperconjugation (refer to page 157); hence, it forms at a faster rate than B. Carbocation B is de-stabilized due to juxtaposition of charges; the highly electronegative fluorine leads to a polar covalent C-F bond with a fractional positive charge on the carbon of the CF 3 group....
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