Proton sponges, such as 1,8- bis(dimethylamino)naphthalene (DMAN). are aromatic diamines characterized by exceptional basicity. For these compounds protonation causes substantial redistribution of electron density which may be traced by observing the changes in structural parameters and in the properties of electron density at bond critical points. On protonation electron density in DMAN goes from the terminal atoms towards the centre of the molecule. This redistribution can also be confirmed by good quality neutron structural data.