IUPAC name of propiophenone is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 1-Phenylpropan-1-one
Propiophenone is a common name: alkyl phenyl ketones are named by adding the name of the acyl group as a prefix to the word phenone. Propionyl (\( \ce{CH3CH2CO} \)–) + phenone gives propiophenone, \( \ce{C6H5-CO-CH2CH3} \).
For the IUPAC name, the longest chain containing the carbonyl carbon has three carbons (propane), the ending –e becomes –one, and the chain is numbered from the end nearer to the carbonyl group:
C6H5–C1O–C2H2–C3H3
The carbonyl group is at C-1 and the phenyl group is also on C-1, so the name is 1-phenylpropan-1-one.
Why the other options are incorrect
Option (1) 2-Phenylpropanone — Incorrect. This is \( \ce{C6H5CH2COCH3} \) (phenylacetone), in which the C=O is at C-2 and the phenyl group on C-1; it is a different compound.
Option (3) Ethyl phenyl ketone — Incorrect. This is the same compound, but it is a common (functional class) name, not the IUPAC name.
Option (4) 1-Phenylethanone — Incorrect. This is the IUPAC name of acetophenone, \( \ce{C6H5COCH3} \), which has one carbon less.
NCERT (2026-27 edition):
Common Names – “… The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. … Alkyl phenyl ketones are usually named by adding the name of acyl group as prefix to the word phenone.”
IUPAC Names – “The IUPAC names of open chain aliphatic aldehydes and ketones are derived from the names of the corresponding alkanes by replacing the ending –e with –al and –one respectively. In case of aldehydes the longest carbon chain is numbered starting from the carbon of the aldehyde group while in case of ketones the numbering begins from the end nearer to the carbonyl group.”