Question

Which from following is a correct priority order for selection of principal functional group for nomenclature of polyfunctional compound according to IUPAC system ?

• A. \(-\text{CHO} > -\text{CONH}_2 > -\text{OH} > -\text{C}\equiv \text{C}-\)
• B. \(-\text{CONH}_2 > -\text{CHO} > -\text{OH} > -\text{C}\equiv \text{C}-\)
• C. \(-\text{C}\equiv \text{C}- > -\text{OH} > -\text{CONH}_2 > -\text{CHO}\)
• D. \(-\text{C}\equiv \text{C}- > -\text{CHO} > -\text{CONH}_2 > -\text{OH}\)

Hint:

Amide ranks above aldehyde, then alcohol, then alkyne.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
When a molecule has more than one functional group, IUPAC picks one as the principal group using a fixed priority list. It becomes the suffix of the name.

Step 2: Key Order:
The general priority is: carboxylic acid > sulphonic acid > anhydride > ester > acid halide > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyne.

Step 3: Detailed Explanation:
From the list, the four groups in the question rank as amide \(-\text{CONH}_2\) first, aldehyde \(-\text{CHO}\) second, alcohol \(-\text{OH}\) third, and alkyne \(-\text{C}\equiv\text{C}-\) last:
\[ -\text{CONH}_2 > -\text{CHO} > -\text{OH} > -\text{C}\equiv\text{C}- \]
This matches option (B).

Step 4: Why the other options are wrong.
Option (A) puts the aldehyde above the amide, which is the wrong way round. Options (C) and (D) place the alkyne first, but alkynes are among the lowest priority groups, below alcohols and aldehydes.

Final Answer:
The correct order is amide, aldehyde, alcohol, alkyne, option (B). \[ \boxed{-\text{CONH}_2 > -\text{CHO} > -\text{OH} > -\text{C}\equiv\text{C}-} \]