How many of the following pairs of common name and IUPAC name are correctly matched?
(i) Acrolein – Prop-2-enal
(ii) Valeraldehyde – Pentanal
(iii) Methyl n-propyl ketone – Pentan-3-one
(iv) Isobutyraldehyde – 2-Methylpropanal
(v) Phthaldehyde – Benzene-1,3-dicarbaldehyde
(vi) Mesityl oxide – 4-Methylpent-3-en-2-one
(vii) α-Methoxypropionaldehyde – 3-Methoxypropanal
(viii) Diisopropyl ketone – 2,4-Dimethylpentan-3-one
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 5
Write the structure behind each common name, then name it by the IUPAC rules: in aldehydes the chain is numbered from the carbon of the –CHO group; in ketones the numbering begins from the end nearer to the carbonyl group. In common names, the α-carbon is the one directly linked to the aldehyde group.
Correctly matched:
(i) Acrolein, \( \ce{CH2=CHCHO} \) — prop-2-enal
(ii) Valeraldehyde, \( \ce{CH3CH2CH2CH2CHO} \) — pentanal
(iv) Isobutyraldehyde, \( \ce{(CH3)2CHCHO} \) — 2-methylpropanal
(vi) Mesityl oxide, \( \ce{(CH3)2C=CHCOCH3} \) — 4-methylpent-3-en-2-one
(viii) Diisopropyl ketone, \( \ce{(CH3)2CHCOCH(CH3)2} \) — 2,4-dimethylpentan-3-one
Not matched:
(iii) Methyl n-propyl ketone, \( \ce{CH3COCH2CH2CH3} \) — the carbonyl carbon is C-2: pentan-2-one.
(v) Phthaldehyde — the two CHO groups are on adjacent ring carbons: benzene-1,2-dicarbaldehyde.
(vii) α-Methoxypropionaldehyde, \( \ce{CH3CH(OCH3)CHO} \) — the α-carbon is C-2: 2-methoxypropanal.
Correctly matched pairs: (i), (ii), (iv), (vi) and (viii) = 5.
NCERT (2026-27 edition):
8.1.1 Nomenclature – “…The α-carbon being the one directly linked to the aldehyde group, β- carbon the next, and so on.”
“…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.”
“The common and IUPAC names of some aldehydes and ketones are given in Table 8.1.”
Table 8.1: Common and IUPAC Names of Some Aldehydes and Ketones
