Resonance-assisted hydrogen bonding in terms of substituent effect

A quantitative description of resonance-assisted H-bond in terms of σ-scale of substituent effect for proton-donating and proton-accepting groups is presented. Application of the proposed approach to malonaldehyde and ortho-hydroxybenzaldehyde shows that formation of H-bonding significantly changes the electronic properties of interacting groups expressed by σ-values, which furthermore explains the increase of π-electron delocalization in such RAHB systems. The presented analyses are based on quantum-chemical modelling at B3LYP/6-311+G∗∗ level.