Elimination reactions Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following alkenes is the major product obtained from the acid-catalyzed dehydration of 3,3-dimethyl-2-butanol?

   • A) 3,3-dimethyl-1-butene
   • B) 4-methyl-2-pentene
   • C) 2,3-dimethyl-1-butene
   • D) 2,3-dimethyl-2-butene
2. 2.

   Which sequence of mechanistic steps defines the $\text{E1cB}$ (elimination unimolecular conjugate base) pathway?

   • A) Concerted abstraction of the $\beta$-proton and departure of the leaving group via a single transition state
   • B) Rate-determining ionization of the substrate to form a carbocation intermediate, followed by rapid deprotonation
   • C) Deprotonation of the substrate to generate a carbanion intermediate, followed by expulsion of the leaving group
   • D) Attack of the base at the leaving-group carbon to form a pentacoordinate intermediate, followed by hydride elimination
3. 3.

   Which of the following reaction conditions most effectively favors an $\text{E1}$ pathway over an $\text{E2}$ pathway for the elimination reaction of a tertiary alkyl halide?

   • A) Using a high concentration of a strong, unhindered base in an aprotic solvent
   • B) Employing a sterically hindered strong base such as potassium tert-butoxide
   • C) Decreasing solvent polarity to suppress ionization of the carbon–halogen bond
   • D) Using a weak base in a polar protic solvent
4. 4.

   In a bimolecular elimination ($\text{E2}$) reaction, which stereoelectronic alignment between the leaving group and the $\beta$-hydrogen atom is required in the transition state to achieve optimal orbital overlap?

   • A) Syn-clinal arrangement with a dihedral angle of 60°
   • B) Anti-periplanar arrangement with a dihedral angle of 180°
   • C) Syn-periplanar arrangement with a dihedral angle of 0°
   • D) Orthogonal arrangement with a dihedral angle of 90°
5. 5.

   Which of the following is the major alkene product formed when 2-bromo-2-methylbutane undergoes elimination in the presence of sodium ethoxide?

   • A) 2-Methylbut-1-ene
   • B) 3-Methylbut-1-ene
   • C) 2-Methylbut-2-ene
   • D) 2-Ethoxy-2-methylbutane