In p. 137 of John D. Clark's Ignition! (in the new edition), Clark reports an interesting observation regarding the shock sensitivity of different isomers of alkyls and ammonium salts.

Specifically, he says that he compared the sensitivity of tetramethyl ammonium nitrate ("Tallulah") in $\ce{N2O4}$ with the isomeric chain ion $\ce{NH3+CH2CH2CH2CH3}$, with the latter being far more sensitive (58 cards vs 8 cards, on his card-gap test setup, which he explains in p. 69).

And, analogously, he compared neopentane with pentane (i.e. the same structures, swapping out $\ce{N+}$ for $\ce C$, again in $\ce{N2O4}$), and again got a fifty-card difference between the two, with pentane testing at 100 cards and neopentane much more stable at 50 cards:

Again a difference of 50 cards, which meant that the ratio of the critical shock wave pressures due to structure was the same in both systems. I was fascinated by this coincidence, but never had the chance to carry the work any further. It's recommended to the attention of some future investigator.

Has this observation been followed up on? If so, what explains the coincidence?

  • $\begingroup$ @Mithoron Which aspects of the question would benefit from bibliographic references beyond the one that's already provided? $\endgroup$ Mar 2, 2019 at 22:23
  • $\begingroup$ Ah, there's only a parallel, still I'm curious is the test for hydrocarbons in mix with N2O4 too? $\endgroup$
    – Mithoron
    Mar 2, 2019 at 22:58
  • $\begingroup$ @Mithoron Identical molar mixtures with dinitrogen tetroxide, yes. $\endgroup$ Mar 2, 2019 at 23:12


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