Theoretical study of strong hydrogen bonds between neutral molecules.The case of amine oxides and phosphine oxides as hydrogen bond acceptors
A theoretical study of the ability of amine oxides and phosphine oxides as hydrogen bond (HB) acceptors has been carried out using ammonium oxide, trimethylamine oxide, and phosphine oxide as model systems. The analysis of the energetic results indicate that only small spatial preferences are observed in the HB interaction. The value of the interaction energies are in several cases within the range of strong HB (>12 kcal/mol), and in complexes between amine oxides and strong acids in the gas phase, a spontaneous proton transfer is obtained. A logarithmic correlation between the electron density at the HB critical points and the HB distance that is able to fit not only calculated data but also experimental ones has been obtained. Finally, a linear relationship has been found between the number of HBs and the 31P NMR shielding in the H3PO···(HF)n series, in good agreement with experimental reports.