Fundamentals of Organic ChemistryChemistryHaloalkanes and Haloarenes
Consider the following two substitution reactions: Reaction I: Reaction II: Which of the following correctly identifies the faster reaction and its predominant mechanism?
Options
- AReaction II is faster and proceeds via an S _ N 1 mechanism.
- BReaction II is faster and proceeds via an S _ N 2 mechanism.
- CReaction I is faster and proceeds via an S _ N 1 mechanism.
- DReaction I is faster and proceeds via an S _ N 2 mechanism.
Correct answer
B. Reaction II is faster and proceeds via an S _ N 2 mechanism.
Step-by-step solution
The given reactions involve 1-bromopropane, which is a primary alkyl halide. Primary alkyl halides undergo nucleophilic substitution predominantly via the S_N2 mechanism due to minimal steric hindrance. The solvent used is DMF (N,N-dimethylformamide), which is a polar aprotic solvent. Polar aprotic solvents favor S_N2 reactions because they do not strongly solvate anions (nucleophiles) through hydrogen bonding, thereby increasing their reactivity. To determine which reaction is faster, we must compare the nucleophi