MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms IV: Elimination / Substitution vs elimination competition
JEE Advanced levelSingle correct optionDifficulty 3 of 3o4091

Assertion (A): Sodium ethoxide converts 2-bromo-2-methylpropane mainly into 2-methylpropene, while 1-bromopropane gives mainly propyl ethyl ether. Reason (R): at the tertiary carbon SN2 attack is blocked by the three alkyl groups, while ethoxide, a strong base, can still remove an easily reached beta hydrogen.

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

Answer: A

Tertiary halides cannot undergo backside SN2 attack because three alkyl groups shield the carbon, while the nine unhindered beta hydrogens are readily available to the base, so E2 wins. For the primary halide the carbon is open to attack, so SN2 (ether formation) dominates. R correctly explains A.
Practice Organic Reaction Mechanisms IV: Elimination More on Substitution vs elimination competition
Previous questionNext question

More questions on Substitution vs elimination competition