Spanning and expanding the basicity scale with simple ammonia derivatives

The currently known intrinsic basicity (Delta G degrees) range spans about 154 kcal/mol, from the basicity of the oxygen molecule (94.7 kcal/mol) to that of 7-isopropyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (248.4 kcal/mol). In this paper, we show that the basicities of two commercially available derivatives of ammonia, viz. F3N and Li3N, differ by 182 kcal/mol, which is greater than the above-mentioned range. We also show that the basicity range from F3N to Li3N can be spanned with simple ammonia derivatives containing single-atom substituents of electronegativity higher or lower than that of nitrogen and that basicities even higher than that of Li3N (a superbase) are indeed possible. The large basicity differences exhibited by these compounds are analyzed in the light of the energies of their charged and neutral forms. It should be noted that the most basic compounds reported fill the current gap between the intrinsic acidity and basicity scales, which allows such basic substances to be inserted in the known acidity range for neutral compounds in order to generate the corresponding conjugate charged forms by reacting in the gas phase an appropriate acid with a neutral base.