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Alcohols and thiols use the -ol and -thiol suffixes, with the OH or SH carbon included in the main chain and numbered to give the functional group the lowest position. Ethers are named either as alkoxyalkanes or as ether-functional-group compounds, depending on which functional group is principal.
Name alcohols and thiols, ensuring the OH/SH carbon is part of the main chain count and gets the lowest number. Compare naming of ethers as alkoxy-substituted alkanes versus as principal ethers.
You already know how to name alkanes using IUPAC rules — find the longest chain, number it, and attach substituent prefixes. Naming oxygenated compounds follows the same logic, but now the oxygen-containing functional group takes priority and determines the suffix. Think of it as adding a new rule on top of the naming system you already have: the functional group gets the lowest possible locant, and the suffix changes to reflect what kind of oxygen is present.
For alcohols (R–OH), replace the final -e of the parent alkane with -ol. The hydroxyl group must be part of the longest chain, and you number the chain so the –OH carbon gets the lowest possible number. For example, butan-2-ol tells you the parent chain is four carbons long and the hydroxyl is on carbon 2. If there are multiple hydroxyl groups, use -diol, -triol, and so on (ethane-1,2-diol for ethylene glycol). Thiols (R–SH) follow the same pattern but use the suffix -thiol instead — ethanethiol is the sulfur analog of ethanol.
Ethers (R–O–R') are handled differently because the oxygen bridges two carbon groups rather than terminating the chain. The IUPAC approach names the smaller group as an alkoxy substituent on the larger parent chain. For instance, methoxyethane describes a methyl group connected through oxygen to an ethane chain. This "alkoxy-as-substituent" method works cleanly when the ether is the only functional group. When a higher-priority group is present — say a hydroxyl or a carbonyl — the ether oxygen is always named as the alkoxy substituent, never as the principal suffix.
The critical skill is recognizing functional group priority. IUPAC rules rank functional groups in a strict hierarchy: carboxylic acids outrank aldehydes, which outrank ketones, which outrank alcohols, which outrank ethers. Only the highest-priority group gets the suffix; everything else becomes a prefix or substituent. A molecule with both an –OH and an ether linkage is named as an alcohol with an alkoxy substituent, not the other way around. Practicing this hierarchy with molecules that contain multiple oxygen-based groups is the fastest way to build reliable naming fluency.