Question

Give IUPAC name of the final product Z.

• A. Mesityl oxide
• B. 4-Methylpent-3-en-2-one
• C. 4,4-Dimethylbut-3-en-2-one
• D. 2-Methylpent-2-en-4-one

Hint:

Hydration of terminal alkyne in presence of \(\mathrm{HgSO_4/H_2SO_4}\) gives a methyl ketoneAlso, nitrile with Grignard reagent followed by hydrolysis gives ketoneWhen two molecules of acetone undergo aldol condensation followed by dehydration, mesityl oxide is formed, whose IUPAC name is 4-Methylpent-3-en-2-one.

Answer 1

The Correct Option is B

Step 1: Find product \([X]\) from propyne.
Propyne undergoes hydration in the presence of \(\mathrm{HgSO_4/H_2SO_4}\).
This is Markovnikov addition of water to the alkyne, giving first an enol, which then tautomerises to a ketone.
\[ \mathrm{CH_3-C \equiv CH \xrightarrow[\mathrm{H_2SO_4}]{\mathrm{HgSO_4}} CH_3COCH_3} \] So, \([X]\) is propanone (acetone).

Step 2: Find product \([Y]\) from ethanenitrile.
Ethanenitrile \(\mathrm{CH_3CN}\) reacts with methyl magnesium bromide \(\mathrm{MeMgBr}\).
Grignard reagent adds to nitrile carbon and on acidic hydrolysis gives a ketone.
\[ \mathrm{CH_3CN \xrightarrow[(B)\ H_3O^+]{(A)\ CH_3MgBr} CH_3COCH_3} \] So, \([Y]\) is also propanone (acetone).

Step 3: Reaction between \([X]\) and \([Y]\) in presence of \(\mathrm{Ba(OH)_2}\).
Since both \([X]\) and \([Y]\) are acetone, the reaction is aldol condensation of acetone.
Under basic conditions, two molecules of acetone first give diacetone alcohol, which on heating undergoes dehydration.
First aldol addition:
\[ 2\mathrm{CH_3COCH_3} \xrightarrow{\mathrm{Ba(OH)_2}} \mathrm{CH_3COCH_2C(OH)(CH_3)_2} \] On heating, dehydration occurs:
\[ \mathrm{CH_3COCH_2C(OH)(CH_3)_2 \xrightarrow{\Delta} CH_3COCH=C(CH_3)_2} \] Thus, final product \([Z]\) is:
\[ \mathrm{CH_3COCH=C(CH_3)_2} \]
Step 4: Write the IUPAC name of \([Z]\).
Now name the compound \(\mathrm{CH_3COCH=C(CH_3)_2}\).
The longest chain containing the ketone group has 5 carbon atoms.
Numbering is done so that the ketone gets the lowest possible locant.
So the structure is named as:
\[ \text{4-Methylpent-3-en-2-one} \]
Step 5: Match with the given options.
The correct option is:
\[ \boxed{(B)\ 4\text{-Methylpent-3-en-2-one}} \] Final Answer:
\[ \boxed{4\text{-Methylpent-3-en-2-one}} \]