Gas-Phase Basicity of Polyfunctional Amidinazines:  Experimental Evidence of Preferred Site(s) of Protonation

Gas-phase basicities of four polyfunctional N 1,N 1-dimethyl-N 2-azinylformamidines (1−4) are obtained from proton-transfer equilibrium constant determinations, using Fourier transform ion-cyclotron resonance mass spectrometry. Comparison with model amidines and azines (GB revised according to the recent compilation of Hunter and Lias) indicates the aza group as the favored site of protonation. The strong basicity of ortho derivatives is explained in term of intramolecular stabilization (the so-called “internal solvation”).