Chapter 13 — Quiz
Twenty-five questions. The decision framework workout.
1. Methyl halide + nucleophile, polar aprotic solvent, room T: (a) always SN2 (b) sometimes SN1 (c) E2 if base is bulky (d) depends on nucleophile
2. Tertiary halide + strong base + heat: (a) SN2 (b) E2 (c) SN1 (d) E1
3. Bulky base on a primary alkyl halide: (a) SN2 dominant (b) E2 (Hofmann) dominant (c) no reaction
4. Polar aprotic solvent favors: (a) SN2 (b) SN1 (c) E1
5. High temperature favors: (a) substitution (b) elimination (c) neither
6. 2° halide + strong nu (NaCN) + polar aprotic + room T: (a) SN2 main (b) SN1 main (c) E1 main (d) E2 main
7. Weak nucleophile = neutral solvent molecule means: (a) SN2 (b) SN1/E1 path (c) E2 (d) no reaction
8. Silver salts (like $AgNO_3$) promote: (a) SN2 (b) SN1 (via halide precipitation, leaving group is "helped" out) (c) E2 (d) no effect
9. t-butyl + methanol at 60°C: (a) SN1 or E1 (b) SN2 (c) no reaction
10. Primary halide + t-butoxide, hot: (a) SN2 (b) E2 (Hofmann) (c) SN1 (d) E1
11. Why does methyl halide always do SN2? (a) No β-H, so no elimination possible (b) Very fast SN2 due to low steric crowding (c) Both (a) and (b) (d) None of the above
12. Why doesn't a tertiary halide do SN2? (a) Steric blockade in the TS (b) Tertiary cation forms first (c) Tertiary halides are less reactive (d) Base attacks the β-H instead
13. Why does heating shift toward elimination? (a) Higher entropy from making a gas (alkene) (b) Higher activation energy is overcome (c) Both (a) and (b) (d) Neither
14. Polar protic solvent + tertiary substrate at room T: (a) SN2 (b) SN1 + E1 mix (c) E2 only (d) no reaction
15. Polar aprotic solvent + 2° substrate + strong nu: (a) SN2 (b) SN1 (c) E2 (d) E1
16. Hofmann elimination is preferred when: (a) bulky base (b) small base (c) polar protic (d) low T
17. A reaction shows: 1st-order kinetics, racemic product, rearrangement. Mechanism? (a) SN2 (b) SN1 (c) E2 (d) E1
18. A reaction shows: 2nd-order kinetics, inverted product, no rearrangement. Mechanism? (a) SN2 (b) SN1 (c) E2 (d) E1
19. A reaction shows: 2nd-order kinetics, alkene product, anti-periplanar geometric requirement. Mechanism? (a) SN2 (b) SN1 (c) E2 (d) E1
20. Why does increasing T shift SN1/E1 ratio toward E1? (a) Entropy favors making a gas (b) Higher activation energy of E1 favored at higher T (thermodynamic accessibility) (c) Both (a) and (b) (d) Neither
21. Match conditions to the mechanism: 2-bromobutane + KO-tBu in t-BuOH at 80°C. (a) SN2 (b) SN1 (c) E2 (Hofmann) (d) E1
22. Match: 2-bromopropane + NaCN in DMSO at 25°C. (a) SN2 (b) SN1 (c) E2 (d) E1
23. Match: $(CH_3)_3CCl$ in 50% aq EtOH at 70°C. (a) SN2 (b) SN1 + E1 (c) E2 (d) Hofmann
24. Match: 2-bromocyclohexane + NaSH in DMF at 25°C. (a) SN2 (b) SN1 (c) E2 (d) E1
25. Why is Chapter 13 the most important chapter in Part III? (a) It unifies the four substitution/elimination mechanisms into one framework. (b) It's needed for every later chapter that uses alkyl halide chemistry. (c) Both (a) and (b). (d) It's not particularly important.
Answer key
- a. 2. b. 3. b. 4. a. 5. b. 6. a. 7. b. 8. b. 9. a. 10. b. 11. c. 12. a. 13. c. 14. b. 15. a. 16. a. 17. b. 18. a. 19. c. 20. c. 21. c. 22. a. 23. b. 24. a. 25. c.