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Why is this the correct name for this compound? I understand the 2,4-dichloro part, but...

  1. Why is it a phenol if there is no hydroxyl group directly bonded to the hydrocarbon ring?

  2. Why is it an acetic acid if it has a CH2COOH instead of a CH3COOH branch on it?


For reasons passing understanding, a cyclic, aromatic, $\ce{C6H5}$ radical fragment (so a benzene minus one $\ce{H}$) is called "phenyl" for the purpose of nomenclature.

I doubt that "2,4-dichlorophenylacetic acid" is a truly IUPAC conforming name, so I'll outline the evolution of this name instead. First, there is acetic acid. You substitute one of the methyl $\ce{H}$s by phenyl: phenylacetic acid (tough to get nowadays, thanks to meth cookers). Now you substitute chlorine atoms for $\ce{H}$s on phenyl, voila.

Note that substitution here is conceptual, not chemical - one would synthesize this very differently.

  • 2
    $\begingroup$ I only had a brief flip through the Blue Book, but if I am not mistaken the PIN for this compound is probably (2,4-dichlorophenyl)acetic acid, as parentheses are required around compound substituents. $\endgroup$ – orthocresol Jan 18 '18 at 1:38

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