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If ammonia, $\ce{NH3}$, is protonated, it becomes ammonium: $\ce{NH4+}$.

If piperidine is protonated, it becomes piperidinium:

piperidine protonation reaction

If piperazine is protonated once, what does it become? By analogy, I would assume piperazinium:

piperazine first protonation

If the resulting monocation is protonated again, what does it then become? The best I've come up with are piperazine dication and piperazin-dium, but that latter seems really awkward:

piperazine second protonation

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2 Answers 2

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The relevant rule in the current (corrected) version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) is:

P-73.1.1.2 General rule for systematically naming cationic centers in parent hydrides

A cation derived formally by adding one or more hydrons to any position of a neutral parent hydride (listed in Chapter P-2), or whose degree of hydrogenation has been modified (see P-31) is named by replacing the final letter ‘e’ of the parent hydride name, if any, by the suffix ‘ium’, preceded by multiplying prefixes ‘di’, ‘tri’, etc. to denote the multiplicity of identical cationic centers. (…)

Therefore, the preferred IUPAC names are piperazin-1-ium and piperazine-1,4-diium, respectively.

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  • $\begingroup$ "... by replacing the final letter ‘e’ of the parent hydride name, if any, by the suffix ‘ium’, preceded by multiplying prefixes..." Shouldn't it be 'piperazin-1,4-diium', without the 'e' immediately before the locants? $\endgroup$
    – hBy2Py
    Commented Apr 18, 2018 at 21:26
  • $\begingroup$ @hBy2Py The elision of vowels is described in more detail in Subsection P-16.7: “Vowels are systematically elided as follows: (a) the terminal letter ‘e’ in names of parent hydrides (…) when followed by a suffix or an ending beginning with ‘a’, ‘e’, ‘i’, ‘o’, ‘u’, or ‘y’;” Therefore, it’s “piperazinium” but “piperazinediium”. $\endgroup$
    – user7951
    Commented May 6, 2018 at 19:53
  • $\begingroup$ Interesting. Obviously not the way I would've initially thought to do it, but I can see the logic. Thanks! $\endgroup$
    – hBy2Py
    Commented May 7, 2018 at 3:20
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Thanks to AvnishKabaj reminding me of ChemSpider's structure search, the names for these compounds are piperazin-1-ium and piperazinediium.

Interestingly, the IUPAC name for the singly protonated species appears to require the locant for the protonated nitrogen, despite its being nominally superfluous, likely due to logic similar to the methyl group in the hydrocarbon discussed in this question.

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