Question

The IUPAC name of:

A) 5-Oxo-4-hydroxy-2-pentanone.
B) 4-Hydroxy-5-al-2-pentanone.
C) 2-Hydroxy-4-oxopentanal
D) 1-al-4-oxo-2-pentanol

Answer 1

Given compound is a polyfunctional compound. Recall the rules for the naming of polyfunctional compounds. In case of polyfunctional compounds, one of the functional groups is chosen as the principal functional group and then further naming is done on that basis. The choice of the principal functional group is made on the basis of order of preference and you should know that order to answer this question.

Complete answer:
Given compound is:

In the above compound, there are three functional groups and these are: Ketone ($- C = O$), alcohol ($- OH$), and aldehyde ($- CHO$). Since the compound contains three functional groups, it is considered as a polyfunctional compound.
In case of polyfunctional compounds, one of the functional groups is chosen as the principal functional group and the compound is further named on that basis. The identified principal functional group determines the choice of appropriate suffix. The remaining functional groups are named as substituents using the appropriate prefixes.
Now, the choice of principle functional group in the given compound will be made on the basis of order of preference. The order of decreasing priority for the required three functional groups is:
$- CHO > - C = O > - OH$
Therefore, the principal functional group will be aldehyde ($- CHO$); hence the parent chain will be suffixed with ‘al’. Numbering of the chain will start from $- CHO$ functional group. The longest chain including $- CHO$ group contains 5 carbon atoms, hence the parent chain will be named as pentanal. The keto ($- C = O$) group in the chain at carbon 4 is indicated by ‘oxo’ and the alcohol group ($- OH$) at carbon 2 is indicated by ‘hydroxy’.
Therefore, on concluding the above explanation, the IUPAC name of the given compound is:
2-Hydroxy-4-oxopentanal.

Hence, option C is correct.

Note: Some functional groups and their IUPAC suffix and IUPAC prefix:

Class of compounds	Functional group structure	IUPAC prefix	IUPAC suffix
Alcohols	$- OH$	hydroxy-	-ol
Aldehydes	$- C = O$	formyl, or oxo	-al
Ketones	$- CHO$	oxo-	-one