Theoretical prediction of hydrogen bond basicity

Abstract

Ab initio and DFT calculations on around 50 hydrogen bond, or Lewis bases and their complexes with hydrogen fluoride are reported. A range of calculated properties of both free bases and complexes are correlated with β, an experimental scale of hydrogen bond basicity. For the entire range of bases, we find that none of the isolated base properties correlate well with β, although some family-dependent models can be constructed for O and N bases separately. In contrast, several properties of the HF complexes and changes on complexation correlate strongly with β, including the H-bond binding energy, changes in the electron density at bond critical points, and the lengthening and weakening of the H–F bond on H-bond formation. Using these models, new values of β are predicted for molecules and functional groups which have no experimentally measured counterparts, including carbenes, C-ylides, phosphines, and amine and phosphine oxides.