MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms III: Nucleophilic Substitution / SN2 mechanism, rate, stereochemistry, steric effects
JEE Main levelSingle correct optionDifficulty 2 of 3o3068

Assertion (A): Neopentyl bromide , a primary halide, undergoes SN2 with in acetone much more slowly than isopropyl bromide, a secondary halide. Reason (R): The three methyl groups on the carbon next to the reacting carbon screen the backside of the C-Br carbon in the SN2 transition state. Choose the correct option.

  1. AA is true but R is false.
  2. BBoth A and R are true and R is the correct explanation of A.
  3. CA is false but R is true.
  4. DBoth A and R are true but R is not the correct explanation of A.

Answer: B

Neopentyl bromide is extremely unreactive in SN2 (its rate constant is thousands of times smaller than that of isopropyl bromide), so A is true. The cause is beta-branching: the bulky tert-butyl group blocks the approach of the nucleophile along the C-Br axis from behind. R is true and explains A.
Practice Organic Reaction Mechanisms III: Nucleophilic Substitution More on SN2 mechanism, rate, stereochemistry, steric effects
Previous questionNext question

More questions on SN2 mechanism, rate, stereochemistry, steric effects