1 (166)

Prévia do material em texto

128 Chapter 7 FURTHER REACTIONS OF HALOALKANES: UNIMOLECULAR SUBSTITUTION AND PATHWAYS OF ELIMINATION Substitution or elimination? Analysis: Factor Favors SUBSTRATE is primary: unhindered Substitution NUCLEOPHILE is strongly basic Elimination NUCLEOPHILE is sterically unhindered Substitution Result: Substitution, to form CH₃CH₂CH₂CH₂NH₂. The text summarizes the preferences for El, E2, SN1, and SN2 reactions for 1°, 2°, and 3° haloalkanes, as a function of reaction conditions, in quite a bit of detail. The chart that follows repeats the same material, again somewhat oversimplified for clarity (solvent effects are not included, for instance). SUMMARY CHART Major reactions of haloalkanes with nucleophiles Type of nucleophile Weakly basic Strongly basic Strongly basic Poor good unhindered hindered Type of nucleophile nucleophile nucleophile nucleophile halide like like like CH₃O⁻ like (CH₃)₃CO⁻ Methyl No reaction SN2 SN2 SN2 1° No reaction SN2 E2 - 2° Slow SN2 E2 E2 3° and E1 and E2 E2 Solutions to Problems OCH₂CF₃ 25. (a) (CH₃)₃COCH₂CH₃ (b) (CH₃)₂CCH₂CH₃ CH₃ CH₃CH₂_OCH₃ (c) (d) C OCH CH₃ H (e) (CH₃)₃COD (f) (CH₃)₃C- 26. (a) For the answer to this part we show each step on a separate line. CH₃ CH₃ CH₃ + Br⁻ CH₃ CH₃