What is the correct IUPAC name of this compound?
I'm not able to understand why the name of this compound is 5-hydroxycyclopent-2-enone and not 2-hydroxycyclopent-4-enone. The -OH group has a higher priority than alkene group so it should be given a smaller number than alkene and hence the name should be 2-hydroxycyclopent-4-enone.
I'm not able to understand why the name of this compound is 5-hydroxycyclopent-2-enone and not 2-hydroxycyclopent-4-enone. The -OH group has a higher priority than alkene group so it should be given a smaller number than alkene and hence the name should be 2-hydroxycyclopent-4-enone.
1 Answer
The correct IUPAC name is 5-hydroxycyclopent-2-enone.
Explanation:
The IUPAC rules for organic nomenclature cover more than 1300 pages.
You may not yet have learned them all.
Here's an edited section on the naming of substituted cycloalkenones.
Insofar as [the preceding rules leave a choice], the starting point and direction of numbering of a compound are chosen so as to give lowest locants to the following structural features … considered successively in the order listed …
(d) the principal group named as a suffix (i.e. -one) …
(f) unsaturation (i.e. -en-)
(g) substituents named as prefixes (i.e. hydroxy)
Thus,
-
the numbering starts with the carbonyl carbon as
#"C1"# -
the first alkene carbon becomes
#"C2"# -
the numbering continues through the double bond and around the ring to
#"C5"#
Thus, the IUPAC name is 5-hydroxycyclopent-2-enone.
