Benchmark binding energies of ammonium and alkyl-ammonium ions interacting with water. Are ammonium–water hydrogen bonds strong?
Abstract
Alkyl-ammonium ion/water interactions are investigated using high level quantum computations, yielding thermodynamics data in good agreement with gas-phase experiments. Alkylation and hydration lead to weaken the NH O hydrogen bonds. Upon complete hydration by four water molecules, their main features are close to those of the OH O bond in the isolated water dimer. Energy decomposition analyses indicate that hydration of alkyl-ammonium ions are mainly due to electrostatic/polarization effects, as for hard monoatomic cations, but with a larger effect of dispersion.