Chem. Eur. J. 24, 1971 – 1977 (2018)

DOI: 10.1002/chem.201705047

Large Proton-Affinity Enhancements Triggered by Noncovalent Interactions

The proton affinity (PA) of the hydroxyl group of a series of compounds YHxOH (x=0–3; Y=Li, Na, Be, Mg, B, Al, Si, P, S, Cl, H) always increases on interaction with Lewis bases (LB=NH3, H2CNH, HCN) according to electronic structure calculations at the G4 level of theory. The LB:YHxOH complexes experience enhancements of PA from 24.8 to 304.8 kJ mol−1 for the OH group with respect to the free compounds. This enhancement is related to the ability of these YHxOH compounds, acting as Lewis acids, to form noncovalent interactions of different kinds. Interestingly, weakly interacting systems can give rise to PA enhancements equal to or even larger than those of strongly interacting systems, as observed in the halogen-bonded complex H2CNH⋅⋅⋅ClOH, whereby the free compound (PA=642.4 kJ mol−1) is transformed into a base (PA=947.2 kJ mol−1) that is stronger than pyridine.