Abstract
The dipole moment of 17 Mannich bases has been measured for a broad range of the intramolecular hydrogen bond strength. The increase of the dipole moment caused by the hydrogen bond formation has been calculated and is discussed in terms of the proton transfer equilibrium.The conformation of the chelate ring was analyzed by means of the atom‐atom and Lippincott‐Schroeder potentials. The calculations predict a nonplanar structure for both the molecular hydrogen bonded form and the zwitterionic proton transfer form. The correlation between the chelate ring structure and the hydrogen bond strength is discussed.