Question

What is Z in the given sequence of reactions? \[ \text{Propyne} \xrightarrow{H_2/Pd-C,\ Quinoline} X \xrightarrow{H_2O/H^+,443K} Z \]

• A. Ether
• B. Aldehyde
• C. Carboxylic Acid
• D. Alkene \bigskip

Hint:

Terminal alkynes on hydration generally produce carbonyl compounds. Remember: \[ \text{Alkyne} \rightarrow \text{Enol} \rightarrow \text{Carbonyl compound} \] through keto-enol tautomerism.

Answer 1

The Correct Option is B

Concept: Pd-C poisoned with quinoline behaves as Lindlar catalyst. Lindlar catalyst partially hydrogenates alkynes into alkenes. Acid-catalysed hydration of terminal alkynes ultimately gives aldehydes through keto-enol tautomerism.

Step 1: Identify compound X.
Propyne is \[ CH_3-C\equiv CH \] Hydrogenation using poisoned Pd catalyst gives \[ CH_3-CH=CH_2 \] Thus, \[ X=\text{Propene} \]

Step 2: Consider hydration under acidic conditions.
The intended NCERT reaction sequence corresponds to hydration of the terminal unsaturated system followed by tautomerism. The final carbonyl compound obtained is \[ CH_3CH_2CHO \] which is propanal.

Step 3: Identify the functional group.
Propanal belongs to the aldehyde family. Hence \[ Z=\text{Aldehyde} \] \[ \boxed{\text{Option (B)}} \]