Substitution reactions Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following primary alkyl halides undergoes nucleophilic substitution at the fastest rate under identical reaction conditions due to possessing the best leaving group?

   • A) 1-Iodobutane
   • B) 1-Bromobutane
   • C) 1-Chlorobutane
   • D) 1-Fluorobutane
2. 2.

   In the electrophilic aromatic substitution of benzene with bromine, what is the primary function of the iron(III) bromide ($FeBr_3$) catalyst?

   • A) It acts as a nucleophile that attacks the aromatic ring to form a tetrahedral intermediate.
   • B) It protonates the benzene ring to increase its susceptibility to halogen attack.
   • C) It coordinates with molecular bromine to generate a more powerful electrophilic species.
   • D) It acts as a Brønsted base to deprotonate the arenium ion in the rate-determining step.
3. 3.

   In the unimolecular nucleophilic substitution ($S_N1$) reaction of a tertiary alkyl halide, which event corresponds to the rate-determining step?

   • A) Attack of the nucleophile on the planar carbocation intermediate
   • B) Proton transfer from the nucleophile to a solvent molecule
   • C) Heterolytic cleavage of the carbon–halogen bond to form a carbocation intermediate
   • D) Simultaneous bond breaking and bond formation via a pentacoordinate transition state
4. 4.

   Which statement correctly characterizes the mechanism and stereochemical outcome of a bimolecular nucleophilic substitution ($S_N2$) reaction at a chiral carbon center?

   • A) It proceeds via a planar carbocation intermediate, resulting in racemization at the chiral center.
   • B) It takes place through a stepwise pathway where the leaving group departs prior to nucleophilic attack.
   • C) It exhibits first-order kinetics with the reaction rate depending solely on substrate concentration.
   • D) It proceeds through a concerted backside attack by the nucleophile, leading to an inversion of configuration.
5. 5.

   Which of the following chemical transformations represents an organic substitution reaction?

   • A) Conversion of propene to propane by reaction with hydrogen gas over a nickel catalyst
   • B) Conversion of 1-chlorobutane to butan-1-ol by reaction with warm aqueous sodium hydroxide
   • C) Conversion of ethanol to ethene by heating with concentrated sulfuric acid
   • D) Conversion of 2-methylpropene to 2-bromo-2-methylpropane by reaction with hydrogen bromide