Phenylpropyne (Ph-C≡C-CH3) undergoes acid-catalysed hydration. What is the major product of this reaction?

Ph-CO-CH2CH3 (phenyl ethyl ketone / propiophenone)
Ph-CH(OH)-CH=CH2
Ph-CH2-CO-CH3 (phenylacetone)
Ph-C(OH)=CH-CH3 (enol intermediate)

Correct answer: Ph-CO-CH2CH3 (phenyl ethyl ketone / propiophenone)

Solution

Protonation of Ph-C≡C-CH3 at the internal carbon bearing CH3 forms the benzylic carbocation Ph-C⁺=CH-CH3. Water attacks to give the enol Ph-C(OH)=CH-CH3, which tautomerises to the more stable ketone Ph-CO-CH2CH3 (propiophenone).

Related JEE Advanced Chemistry questions

Identify the correct combination for preparing benzoic acid using the given starting materials, reaction conditions, and reaction types.
Consider the molecule Ph-CO-CH2-CH2-CO2Me (methyl 4-oxo-4-phenylbutanoate), which contains both a ketone group and a methyl ester group. Which of the following reagents will selectively reduce only the ketone to give Ph-CH(OH)-CH2-CH2-CO2Me, leaving the ester intact?
Which of the following statements is INCORRECT regarding NaBH4?
From the compounds listed below, how many will give a POSITIVE iodoform test but a NEGATIVE Tollens' test? (a) Ethanal (CH3CHO) (b) Propan-2-one (CH3COCH3) (c) Butan-2-ol (CH3CH(OH)CH2CH3) (d) 4-acetylbenzaldehyde (OHC-C6H4-COCH3) (e) Cyclopropyl methyl ketone (cyclopropane ring bearing a -COCH3 group) (f) A cyclopentanone derivative bearing both an aldehyde (-CHO) and an acetyl (-COCH3) substituent (g) Ethanol (CH3CH2OH) (h) Acetic acid (CH3COOH) (i) Acetophenone (C6H5COCH3)
Among the following carboxylic acids, which one undergoes decarboxylation most easily upon heating?
A vinyl ether (cyclohexyl enol ether where one cyclohexyl group is attached to the oxygen and a cyclohexenyl group forms the vinyl part) undergoes acid-catalyzed hydrolysis (H+ / H2O) to give two products P and Q. On treatment with concentrated H2SO4 and heat, P and Q both give the same alkene R of molecular formula C6H10. Identify Q.

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →