Prévia do material em texto

138 Chapter 7 FURTHER REACTIONS OF HALOALKANES: UNIMOLECULAR SUBSTITUTION AND PATHWAYS OF ELIMINATION (b) Rates of (1) and (2) will be the same, or nearly so. (1) is and (2) is and and they have the same rate-determining step; if the reaction mixtures are similar in polarity, the rates will be very close. Rate of (3) will depend on the concentration of the base because of the occurrence of bimolecular elimination. 46. (a) CH₂ E2 (b) No reaction. Poor leaving group. (c) Racemic CH₃CH₂CHOHCH₃ (d) E2 (e) SN2 I (f) Racemic (g) No reaction, except for reversible proton transfer. (h) CH₂CH₂CH₂CN and NC CH₂CH₂CH₂CN E2 and SN2 OCH₃ (i) (j) CH₂CH₃ (k) (I) No reaction. Poor nucleophile. 47. Reagent Haloalkane KOC(CH₃)₃ no reaction SN2 SN2 no reaction SN2 } (CH₃)₂CHOH } (CH₃)₂CHSeCH₃ (CH₃)₃COH } E2 E2 (CH₃)₂C=CH₂ (CH₃)₂C=CH₂ and and 48. See answer to Problem 47. Secondary halides give higher E2/E1 ratios than do tertiary halides (secondary carbocations form less readily than tertiary). 49. (a) Poorly. and are important products. (b) Not at all. No reaction; poor nucleophile.