Q.Give the IUPAC name of $\text{CH}_3\text{COCH}_2\text{CH}_2\text{CH}_3$ and identify the lowest locant given to the carbonyl carbon.

Both families are named by locating the longest chain through the carbonyl carbon and swapping the alkane's '-e' for '-al' (aldehyde) or '-one' (ketone). An aldehyde's carbonyl carbon is ALWAYS C1, since -CHO can only sit at a chain end; a ketone's carbonyl carbon instead gets the LOWEST possible locant among its two numbering directions, since it can sit anywhere along an interior chain -- e.g. pentan-2-one, not pentan-4-one. A second, ketonic carbonyl appearing as a substituent on a chain whose PRIMARY suffix is already '-al' (only one group can be the suffix) is cited instead as an 'oxo-' prefix with its own locant, e.g. 3-oxopentanal. Common names (formaldehyde, acetone, benzaldehyde) remain in constant everyday and exam use alongside the IUPAC names, and are built the same way common names of the corresponding acids are (Section 12.8) -- by substituting a family ending onto a familiar trivial root rather than a systematic chain name.