A 5-high straight flush of water-ionised acids?

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I do not play poker, and so I had to look up a 5-4-3-2-1(A), which Wikipedia informs me is a 5-high straight flush, also apparently known as a steel wheel. In previous posts  I have suggested acids which can be ionised by (probably) 5, 4, 3 or  1 discrete water molecules in the gas phase; now to try to track down  a candidate for ionisation by the required two water molecules to form that straight flush.

As the counter-anion to quaternary ammonium cations, bis(trifluoromethylsulfonyl)imide is a component of some ionic liquids. Its conjugate acid is thought[1],[2] to protonate on the nitrogen.

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My first obvious attempt was to place two waters near that N-H to see if it would ionise from that position.[3] The proton remains attached to the nitrogen(-:

Next, how about re-locating the waters so that they are closer to the sulfonyl oxygens? This time we do have the characteristic hydronium cation forming.[4] However, the free energy of this isomer is +6.7 kcal/mol higher relative to the NH form. So not a 5-high straight flush in a strict sense, but it perhaps does give a hint of how one might design the missing card.

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Confession time. I did spend many a Wednesday afternoon as an undergraduate playing the card game bridge.


  1. Z. Žák, A. Růžička, and C. Michot, "Structures of bis(fluorosulfonyl)imide HN(SO2F)2, bis(trifluoromethylsulfonyl)imide HN(SO2CF3)2, and their potassium salts at 150 K", Zeitschrift für Kristallographie - Crystalline Materials, vol. 213, 1998. http://dx.doi.org/10.1524/zkri.1998.213.4.217
  2. Zak, Z.., and Ruzicka, A.., "CCDC 119129: Experimental Crystal Structure Determination", 1999. http://dx.doi.org/10.5517/CC3ZYWW
  3. Henry S Rzepa., "C 2 H 5 F 6 N 1 O 6 S 2", 2015. http://dx.doi.org/10.14469/ch/191136
  4. Henry S Rzepa., "C 2 H 5 F 6 N 1 O 6 S 2", 2015. http://dx.doi.org/10.14469/ch/191137

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