Basicity of primary amines: a group properties based study of the importance of inductive (electronegativity and softness) and resonance effects

The group properties of substituents are invoked to explain the gas phase proton affinity of a variety of primary amines XNH2. A triple correlation using the group electronegativity, group softness and a resonance parameter of the substituent was successful for interpreting the proton affinity sequence. The group electronegativity and resonance parameter were found to be important in determining this sequence, the group softness being of minor importance. Density functional theory based as well as more traditional quantum chemical properties in the neighbourhood of the nitrogen atom were found to be inadequate for our purpose.