Where to put the number in organic nomenclature? [closed]








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Should one write 4-hydroxypentan-2-one or 4-hydroxy-2-pentanone?
It has been seen that both have been used frequently.




The IUPAC recommendations on this matter have been changed.


According to the 1979 recommendations, the correct name was still 4-hydroxy-2-pentanone.


According to the [1993 recommendations](http://www.acdlabs.com/iupac/nomenclature/93/r93_42.htm), however, locants were placed immediately before the part of the name to which they relate. This rule is still included in the 2013 version. Therefore, the correct name is now **4-hydroxypentan-2-one.**


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