- The protiotetramethylammonium dication (CH3)3NCH42+: Hydrogen/deuterium exchange and calculational studies. Search for the parent protioammonium dication NH52+
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The protonation of ammonium ions NR4+ (R = H, CH3) to form the corresponding protioammonium dications HNR42+ (R = H, CH3) was investigated by hydrogen/deuterium exchange experiments and by ab initio molecular orbital calculations. Hydrogen/deuterium exchange was observed by 2H NMR spectroscopy at the CH3 groups of tetramethylammonium ion N(CH3)4+ when reacted with excess DF:SbF5 superacid. On the basis of calculational results, the intermediacy of the corresponding C-H-protonated protiotetramethylammonium dication (CH3)3NCH42+ is suggested to account for the observed exchange. Under similar conditions, no exchange was observed in the parent ammonium ion NH4+ in FSO3D:SbF5 superacid, although the NH52+ dication was calculated to be kinetically stable with a considerable barrier to deprotonation. The pentafluoroammonium dication NF52+ was also investigated theoretically, and the results were compared to those of neutral NF5.
- Olah, George A.,Burrichter, Arwed,Rasul, Golam,Prakash, G.K. Surya
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- H/D isotope exchange between methane and magic acid (HSO 3F-SbF5): An in situ NMR study
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The kinetics of hydron exchange between methane and a series of DSO 3F-SbF5 superacids were measured by in situ 2H decoupled 1H NMR spectroscopy. The rates of exchange showed a strong dependence on antimony pentafluoride concentration, with the free energy of activation ΔG# (30°C) decreasing from 97 to 84 kJ mol -1 over the range of concentration 19 to 49 mol % SbF5. The constant free enthalpy of activation ΔH# (ca. 65 kJ mol-1) and the decreasing entropy of activation ΔS# seem to indicate that an increase in acidity of the superacid system does not substantially change the nature of the transition state but rather acts on its solvation.
- Walspurger, Stephane,Goeppert, Alain,Haouas, Mohamed,Sommer, Jean
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p. 266 - 269
(2007/10/03)
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