Question
Name the following compound using IUPAC rules:
Solution — Step by Step
Write out the structure and count: C–C–C. Three carbons in the parent chain.
The parent alkane for 3 carbons is propane, so our base name is prop-.
We have an –OH group, which is an alcohol. In IUPAC nomenclature, alcohols get the suffix -ol (replacing the terminal ‘-e’ of the alkane).
Base name becomes: propanol.
We number from the end closest to the –OH group. The –OH is on the terminal carbon, so we number from that end — it gets carbon 1.
If we had numbered from the other end, –OH would be on carbon 3. We always choose the direction that gives the principal group the lowest number.
Parent chain: prop
Suffix for alcohol: -an-1-ol (insert the locant before the suffix)
IUPAC name: Propan-1-ol
Why This Works
IUPAC naming for alcohols follows a strict priority: the –OH group must get the lowest possible locant. This is the principal characteristic group rule — whatever suffix group you’re naming, minimise its position number first, before worrying about substituents.
For a straight-chain 3-carbon alcohol with –OH at the end, the locant is always 1. The name propan-1-ol tells us everything: 3-carbon chain (prop), single bonds throughout (an), alcohol group (ol), located at carbon 1.
This compound is simply common rubbing-alcohol’s smaller cousin — it’s used as a solvent and in pharmaceuticals, but for your exam, it’s the go-to example in every NCERT alcohol chapter.
Alternative Method — Common Name Cross-Check
In organic chemistry practice, you’ll encounter the common name n-propyl alcohol for this structure. While common names aren’t accepted in IUPAC answers, cross-checking helps confirm your structure.
The ‘n’ stands for normal (straight chain), and ‘propyl’ confirms 3 carbons. If your IUPAC name doesn’t correspond to the expected common name, go back and recount.
For straight-chain primary alcohols (–OH on the end carbon), the IUPAC name always ends in -an-1-ol: methanol, ethanol, propan-1-ol, butan-1-ol. Memorise this pattern — it saves time in MCQs.
Common Mistake
Writing “1-propanol” instead of “propan-1-ol”
Many students write the locant before the parent name (American-style: 1-propanol). IUPAC 2013 recommendations require the locant immediately before the suffix it refers to: propan-1-ol, not 1-propanol.
CBSE board answer keys and JEE marking schemes follow IUPAC 2013. In a board exam, writing “1-propanol” may cost you the mark — the examiner is specifically checking for correct locant placement.