Conclusion In the gas-phase FDM* R with R= alkyl are among the strongest organic bases yet known, comparable to tetramethylguanidine and 4-(dimethy1amino) pyridine. Formamidines are protonated on the imino nitrogen atom. The gas-phase basicity depends linearly on the polarizability of alkyl substituents linked to the imino nitrogen. Due to the charge delocalization on the protonated amidine framework the sensitivity to this effect is ...