Which one of the following carbonyl compound cannot be prepared by addition of water on an alkyne in the presence of…
Hydrocarbons · Class 11 · JEE Main Previous Year Question
Which one of the following carbonyl compound cannot be prepared by addition of water on an alkyne in the presence of and ?
- a✓
A
- b
B
- c
C
- d
D
A
Step 1: Hydration mechanism with HgSO4/H2SO4
Markovnikov addition of water to alkyne:
- Terminal alkynes give methyl ketones (OH on internal C)
- Ethyne gives acetaldehyde (only exception)
- Internal alkynes give ketones
Step 2: Evaluate Options
(a) Propanal : An aldehyde where the CHO is at terminal position. To get this from propyne, water must add anti-Markovnikov (OH on terminal C). follows Markovnikov, so this CANNOT be prepared this way. Answer: (a)
(b) Methyl ethyl ketone: From 1-butyne by Markovnikov hydration. Possible.
(c) Cyclohexanone: From cyclohexyne (internal alkyne). Possible.
(d) Acetaldehyde: From ethyne (unique case, gives ). Possible.
Key Points:
- hydration follows Markovnikov rule
- Terminal alkynes give methyl ketones (not aldehydes) except ethyne
- Propanal requires anti-Markovnikov hydration (use hydroboration-oxidation)
Practice this question with progress tracking
Want timed practice with adaptive difficulty? Solve this question (and hundreds more from Hydrocarbons) inside The Crucible, our adaptive practice platform.
More JEE Main Hydrocarbons PYQs
Compound A formed in the following reaction reacts with B gives the product C. Find out A and B.
Metallic sodium does not react normally with:
The major product obtained from the following reaction is:
Consider the following reactions: A is:
Given below are two statements: Statement (I): On nitration of m-xylene with HNO3, H2SO4 followed by oxidation, 4-nitrobenzene-1,3-dicarboxylic acid is obtained as the major product. Statement (II):…