Consequences of proton transfer in guanidine

Consequences of proton-transfer reactions in guanidine in the solid state, solution and gas phase are discussed. Y-delocalization, resonance and symmetry strongly influence the basicity of guanidine in the gas phase. These effects, are, however, insufficient to explain the basicity of guanidine which in aqueous solution is stronger than that of trisubstituted alkylamines and proton. sponge (DMAN). The intrinsic (gas-phase) basicity of guanidine is close to that of triethylamine. The large difference between the basicities of amines and guanidine in solution is attributed to the important role played by effects such as polarizability and internal and external solvation. Copyright (C) 2003 John Wiley Sons, Ltd.