3
$\begingroup$

I found this question online on Jiskha Homework Help:

Of the compounds mercury(II) cyanate, $\ce{Hg(OCN)2},$ and mercury(II) fulminate, $\ce{Hg(CNO)2},$ one is highly explosive, the other is not. Explain.

My teachers says that most explosives are made of nitro compounds as abnormal expansion in $\ce{N-O}$ bond has been observed in nitro compounds above a certain temperature. So, fulminate will be more explosive as it contains $\ce{N-O}$ bond.

According to Wikipedia, explosiveness of nitro and other nitrogen containing compounds (like $\ce{NI3})$ is because of possibility of forming highly inert and stable $\ce{N2}$ molecules. Thus slight amount of energy causes breaking of relatively weaker $\ce{N-O}$ bonds and highly exothermic formation of $\ce{N2}$ triple bond making it act like an explosive.

Is my teacher correct? The reasoning given on Wikipedia also points to fulminate but some other concept may be at play here. So, which is correct? Also what would be the reaction mechanism if any?

$\endgroup$
3
  • 2
    $\begingroup$ "Obligatory" Breaking Bad reference: Fulminated mercury Wiki. As for the question, I bet there is an answer in one of Klapötke's published works:) $\endgroup$
    – andselisk
    Jul 20, 2020 at 6:53
  • 2
    $\begingroup$ @andselisk That Klapötke is alive to write with all fingers and faculties intact is a majestic testament to either walking the razors edge with skill or armed with an unseemly supply of sheer luck. Or both. $\endgroup$
    – Stian
    Dec 17, 2020 at 8:43
  • $\begingroup$ See also Azidoazide azide: Chemistry in its element 12/11/20 by Chemistry World Web player: podcastaddict.com/episode/116426632 Episode: traffic.libsyn.com/secure/chemistryinitselement/… A compound so explosively unstable that nobody has been able to measure how sensitive it is without it, well, exploding. $\endgroup$
    – Poutnik
    Jan 7, 2023 at 13:50

2 Answers 2

0
$\begingroup$

This can be attributed to the formal charges of fulminate ion and cyanate ion. Structural stability of a compound sometimes depend on formal charge.

enter image description here

enter image description here

We observe that formal charges of fulminate ion is higher than cyanate ion for which fulminate ions are said to have a less favorable molecular configurations which leads to facile decomposition of the fulminate ion.

Fulminate vs cyanate stability has been demonstrated by using their corresponding silver compounds. Here is a video demonstration.

$\endgroup$
2
  • 1
    $\begingroup$ In fulminate different minor structures then the ones you included are necessary. Also need for formal charge means virtually nothing on itself. . $\endgroup$
    – Mithoron
    Jul 20, 2020 at 18:16
  • $\begingroup$ I understand that you are saying that fulminate is less stable and thus more explosive, but what the abnormal expansion of N-O bond that my teacher said, have you ever heard of it? $\endgroup$ Jul 21, 2020 at 3:37
0
$\begingroup$

One possible explanation is that compounds with formal postive charges on certain elements, such as nitrogen or chlorine, that are directly adjacent to formal negative charges AND with these charges not being able to be intramolecularly "neutralised" (were it not for formally "hypervalent" resonance contributors) are often explosive. This is evident from the two-year-old answer by Nilay Ghosh- cyanate has no such issues, while fulminate does, the latter being an explicit example in the paper.

*Before you comment things like "hypervalency has been disproven a long time ago" please read this paper.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.