My primary school released a folder which contains some sketches. As you can see, they included two molecules. One of them is isopropanol. What's the name of the other molecule (bottom)? Does it exist? The formula would be $\ce{C8H2N4}$. It needs to be in a pentagon shape. I guess it has something "tri cyano cyclo penta" in the name.

Folder C8H2N4 C8H2N4

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    $\begingroup$ The formula reported in the first and in the second picture are not finished. The nitrogen atom down at left should be attached to two H atoms. These two H atoms are correctly reported in the third picture, with spherical atoms. The total number of H atoms is $4$, and not $2$. $\endgroup$
    – Maurice
    Sep 9, 2021 at 20:07
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    $\begingroup$ I suspect the scribble you are interpreting as as N at the bottom is not related to the structure and that carbon is supposed to be a CH2 group so the core structure is cyclopentadiene and the overall molecule is tricycanocyclopentadiene. $\endgroup$
    – Andrew
    Sep 9, 2021 at 21:02
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    $\begingroup$ Then again, at this level of precision N might well be a part of the structure, and even a part of the ring (as in pyrrole). Who cares. All suggested molecules exist, but are not particularly famous or important. $\endgroup$ Sep 9, 2021 at 21:33

1 Answer 1


Aside apparent possibilities of a made-up structure or structure being a fragment ripped off from a larger heterocycle by the designer, there is a third one. Let's pretend the black dash next to the label ‘N’ on the bottom is a minus sign. Then we have 2,3,4‐tricyano‐1H‐pyrrol‐1‐ide $\ce{C7HN4-}$:


I haven't found this exact structure, but a more symmetrical tetracyanopyrrolide anion $\ce{C8N5-}$ (2,3,4,5-tetracyanopyrrol-1-ide, TCP) is well-known and has been structurally characterized with single crystal diffraction [1] (see also supplementary structures with CSD IDs PEMTOS, PEMTUY and PEMVAG).

tetramethylammonium 2,3,4,5-tetracyanopyrrol-1-ide

Figure 1. Fragment of the crystal structure of tetramethylammonium 2,3,4,5-tetracyanopyrrol-1-ide (CSD ID: PEMTOS). Color code: $\color{#EEEEEE}{\Large\bullet}~\ce{H};$ $\color{#909090}{\Large\bullet}~\ce{C};$ $\color{#3050F8}{\Large\bullet}~\ce{N}.$


  1. Becker, M.; Harloff, J.; Jantz, T.; Schulz, A.; Villinger, A. Structure and Bonding of Tetracyanopyrrolides. Eur. J. Inorg. Chem. 2012, 2012 (34), 5658–5667. DOI: 10.1002/ejic.201200790.
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    $\begingroup$ What an unpleasantly high N:C ratio. This molecule looks like a vicious accident wanting to happen. $\endgroup$
    – Stian
    Sep 10, 2021 at 9:01
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    $\begingroup$ @StianYttervik See nitrogen enriched energetic materials e.g., by the Klapötke group. The military is interested in these. $\endgroup$
    – Buttonwood
    Sep 13, 2021 at 17:23
  • $\begingroup$ @StianYttervik 5:8 ? That's a piece of cake ;) Something like 5:1 and things are interesting :D $\endgroup$
    – Mithoron
    Jan 19, 2022 at 22:13

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