MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms IV: Elimination / Substitution vs elimination outcome for drawn substrates
JEE Advanced levelSingle correct optionDifficulty 3 of 3o4273

The halo ketone shown is stirred with dilute aqueous sodium hydroxide at room temperature. Which description of the major pathway and product is correct?

  1. AE1cB through the enolate, giving 4-hydroxybutan-2-one
  2. BE1 through a primary carbocation, giving but-3-en-2-one
  3. CE1cB through the enolate, giving but-3-en-2-one
  4. DSN2 at the primary carbon, giving 4-hydroxybutan-2-one as the main product

Answer: C

The compound is 4-bromobutan-2-one. The hydrogen on C-3 is alpha to the carbonyl and acidic, so hydroxide forms the enolate quickly. The enolate then expels bromide from the beta-carbon (E1cB), giving the conjugated enone but-3-en-2-one (methyl vinyl ketone). A primary carbocation is not formed, and the hydroxy ketone would be the unconjugated substitution product.
Practice Organic Reaction Mechanisms IV: Elimination More on Substitution vs elimination outcome for drawn substrates
Previous questionNext question

More questions on Substitution vs elimination outcome for drawn substrates