Chapter 12 — Quiz

Twenty-five questions. Answers at the end.

1. $E2$ kinetics: (a) first order (b) second order (c) zero order

2. $E2$ requires the H and X to be: (a) gauche (b) anti-periplanar (c) cis (d) any geometry

3. $E1$ proceeds via: (a) carbocation intermediate (b) concerted single step (c) radical chain (d) cyclic TS

4. Zaitsev product: (a) most-substituted alkene (b) least-substituted alkene (c) both equally (d) inverted

5. Hofmann product is preferred when: (a) bulky base (b) small base (c) high T (d) all of the above

6. Higher temperature favors: (a) substitution (b) elimination (c) neither

7. Tertiary halide + strong bulky base + heat: (a) $S_N1$ (b) $E2$ (c) $S_N2$ (d) $E1$

8. $E1$ kinetics: (a) first-order in substrate, zero-order in base (b) second-order overall (c) zero-order

9. In cyclohexane $E2$, both H and X must be: (a) axial (b) equatorial (c) either works (d) trans

10. Bulky base (KO-tBu) + 2° halide: (a) Zaitsev usually (b) Hofmann due to steric approach (c) no reaction (d) only $S_N2$

11. A reaction is first-order in substrate but zero-order in base. Mechanism? (a) $E1$ (b) $E2$ (c) $S_N2$ (d) any of the above

12. Acid-catalyzed dehydration of an alcohol uses what mechanism? (a) $E1$ (b) $E2$ (c) free radical (d) ionic but not E1

13. A 1° alkyl halide + strong bulky base + heat: (a) $S_N2$ dominant (b) $E2$ Hofmann dominant (c) $S_N1$ (d) no reaction

14. Why is Zaitsev product more stable? (a) Hyperconjugation with alkyl groups (b) Less steric strain (c) Aromatic stabilization (d) None of above

15. A trans-1-bromo-2-methylcyclohexane has the substituents on opposite faces. The E2 reaction requires axial Br. In the chair where Br is axial, what is the configuration of the methyl? (a) axial (b) equatorial (c) doesn't matter (d) trans

16. Cope elimination uses a 5-membered cyclic TS. The geometry is: (a) anti-periplanar (b) syn-periplanar (c) eclipsed (d) anti-clinal

17. Hofmann elimination of $R_4N^+ OH^-$ gives: (a) Zaitsev alkene (b) Hofmann (less-substituted) alkene (c) no alkene (d) only ammonia

18. A 1,3-diaxial relationship between two large substituents in a cyclohexane $E2$ TS: (a) is energetically unfavorable but doesn't matter for the reaction (b) makes E2 of one chair much faster than the other (c) only affects E1 (d) means the reaction can't proceed

19. In $E1$, the rate-determining step is: (a) ionization (carbocation formation) (b) base attacking the β-H (c) the proton transfer (d) nucleophilic attack

20. A reaction shows: 1st order kinetics, gives Zaitsev alkene, occurs in polar protic solvent at high T. Mechanism? (a) $E2$ (b) $E1$ (c) $S_N2$ (d) $S_N1$

21. Why is anti-periplanar geometry the requirement for E2? (a) Bond rotation makes other geometries unstable (b) Orbital overlap of forming π bond requires it (the C-H σ orbital must align with C-X σ* antibonding) (c) Steric clash blocks other geometries (d) All of the above contribute

22. Why is $E2$ on cyclohexane substrates often slower than on acyclic 2° substrates? (a) The cyclohexane requires axial-axial geometry (only one chair conformation can do E2) (b) Cyclohexane can't form anti-periplanar at all (c) Different mechanism (d) Hyperconjugation is different

23. Distinguishing E1 from E2 experimentally: (a) Vary base concentration; rate response indicates E2 (b) Run at different temperatures; T effect indicates mechanism (c) Check for rearrangement (E1 only) (d) All of the above

24. Industrial vinyl chloride is made by: (a) $E2$ on 1,2-dichloroethane at 500°C (b) $E1$ of 2-chloroethanol (c) Direct reaction of HCl with ethylene (d) Free radical halogenation

25. Why would a chemist choose Hofmann elimination over standard E2? (a) When the less-substituted alkene is wanted (b) When the substrate has only an amine, not a halide (c) Both (a) and (b) (d) Hofmann is just a name for E2

Answer key

1. b. 2. b. 3. a. 4. a. 5. d. 6. b. 7. b. 8. a. 9. a. 10. b. 11. a. 12. a. 13. b. 14. a. 15. b (if Br is axial, methyl is equatorial because they were trans on the original ring). 16. b. 17. b. 18. b. 19. a. 20. b. 21. d. 22. a. 23. d. 24. a. 25. c.