Chemistry · Alcohols, Phenols And Ethers · NEET
Pick the LONGEST continuous carbon chain that CONTAINS the carbon bonded to -OH. The -OH group must be on the main chain, even if a longer chain exists elsewhere. First find -OH, then trace the longest chain through it. Drop the final 'e' of the alkane name and add '-ol' (example: propane becomes propan-1-ol).
Number the chain from the end that gives the -OH group the SMALLEST possible number. The -OH always beats a branch (like methyl) when deciding which end to start from. So if -OH can be C2 from one end or C4 from the other, you choose C2. This is the 'lowest locant' rule and it is where most NEET mistakes happen.
You number from the end that gives -OH the lower number. In (CH3)2C(OH)-CH2-CH3 the longest chain is 4 carbons (butane). The -OH is on the second carbon whether you count from the OH end (C2). The methyl branch is also on that carbon (C2). Both give '2', so the name is 2-methylbutan-2-ol. If you numbered from the wrong end, -OH would be C3, which is higher and therefore wrong.
Ethers are named as 'alkoxyalkane'. The LARGER alkyl group becomes the parent alkane (the -ane part), and the SMALLER group becomes the alkoxy prefix. For example CH3-O-C2H5: the larger side is ethane and the smaller side is methoxy, so the name is methoxyethane (common name: ethyl methyl ether). Anisole (C6H5-O-CH3) is methoxybenzene.
The IUPAC name of C6H5-OH is simply 'phenol' (this is a retained/accepted name). For substituted phenols, number the ring so -OH is C1 and the other groups get the lowest locants. Example: 2-nitrophenol has NO2 on C2. Cresols are methylphenols (o-cresol = 2-methylphenol).
When the -OH position ties (same number from both ends), then decide by giving the substituents (branches) the lowest set of locants. If they still tie, use alphabetical order of the substituents. But remember: the functional group -OH always has FIRST priority for the lowest locant, before any branch.
What is the IUPAC name of the organic compound formed in the following reaction? CH3COCH3 (acetone) → (i) C2H5MgBr, dry ether (ii) H2O/H+ → Product
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. The chain is only carbon atoms. The -OH is a substituent group that tells you where to start numbering and what suffix (-ol) to use. Oxygen is never counted as a chain carbon.
The -OH suffix still gets priority for the lowest locant over the double bond. Name it as an 'en-ol', for example but-3-en-1-ol (double bond at C3, OH at C1). The -OH takes the lower number.
No, that is the common (trivial) name. The IUPAC name is methoxyethane. For NEET, know both, because questions may give either the common or IUPAC form in the options.
Glycerol is propane-1,2,3-triol. It has three -OH groups on a 3-carbon chain, so you use the multiplying prefix 'tri' and keep the 'e' of propane before 'triol'.
NEET regularly asks 'IUPAC name of the product' after a reaction (Grignard, hydration, reduction). You must first find the correct structure, then name it correctly. One wrong locant or wrong chain length changes the whole answer, so naming rules directly earn marks.
