SSC CGL 2024 Tier-I · 9 September 2024, Shift 2 · General Awareness · Question 17 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 5 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

What is the IUPAC name of tertiarybutyl alcohol?

(a)1-propylpropan-3-ol
(b)1-ethylpropan-3-ol
(c)1-Methylpropan-3-ol
(d)2-Methylpropan-2-ol

Answer

Why

Correct — D. tert-Butyl alcohol is (CH₃)₃C–OH — one carbon carrying the –OH and three methyl groups.

Rule: the parent chain is the longest chain through the carbon that bears the –OH.

Longest chain here = three carbons → propane.
The third methyl becomes a methyl branch.
–OH takes the lower locant → C2, methyl at C2.

Name: 2-methylpropan-2-ol → option (d).

The prefix tert is itself the clue: the carbinol carbon is joined to three other carbons.

Why the others are wrong

(a)
1-propylpropan-3-ol — Not a legal name. Write it out — propyl on C1 of propane, –OH on C3 — and the chain through the –OH runs six carbons, so the compound is hexan-1-ol, a primary alcohol.
(b)
1-ethylpropan-3-ol — Five carbons, so it is out before you check the class. Ethyl on propane gives pentan-1-ol; tert-butyl alcohol has four carbons in all.
(c)
1-Methylpropan-3-ol — Primary, and 'tert' rules that out. Methyl on propane is butan-1-ol misnumbered — a genuine isomer of tert-butyl alcohol, both C₄H₁₀O, but its –OH sits on a terminal carbon.

Concept

Two rules settle almost every alcohol-naming question.

Parent chain — the longest carbon chain containing the carbon that bears the –OH. Anything left over is a substituent.

Numbering — the chain is numbered so the –OH takes the lowest possible locant. Substituent numbers follow from that choice, never the reverse.

The four alcohols of formula C₄H₁₀O are worth memorising outright:

n-butyl alcohol = butan-1-ol
sec-butyl alcohol = butan-2-ol
isobutyl alcohol = 2-methylpropan-1-ol
tert-butyl alcohol = 2-methylpropan-2-ol

Options (a) to (c) are not merely wrong answers — none of them is a legal IUPAC name. Each keeps a three-carbon parent when a longer chain through the –OH exists.

Key facts

tert-Butyl alcohol, (CH₃)₃C–OH, is 2-methylpropan-2-ol in IUPAC nomenclature.
An alcohol is primary, secondary or tertiary according to whether the –OH carbon is bonded to one, two or three other carbons.
The parent chain is the longest chain containing the –OH carbon, and that carbon takes the lowest locant.
C₄H₁₀O has four alcohol isomers: butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol.

Study next

Common name to IUPAC conversions for small molecules — acetic acid, acetone, formaldehyde, glycerolPrimary, secondary and tertiary alcohols, and how the class changes the oxidation productFunctional group priority and suffix selection when more than one group is present

Common traps

Naming the longest chain in the molecule instead of the longest chain through the –OH carbon.
Fixing the substituent's number first and letting the –OH take whatever locant is left.
Picking the most complicated-looking option because the common name sounds complicated.

SSC's chemistry in General Awareness stays at naming and everyday identity — a common name to convert, a formula to match, a use to recall. Never mechanisms.

Related PYQs

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