Charge density distribution in the "proton sponge" compound 1,8-bis(dimethylamino)naphthalene

This is the first low-temperature, high-resolution X-ray and neutron diffra ction study of charge distribution in an uncomplexed proton sponge compound . In the parent compound of this class, 1,8-bis(dimethylamino)naphthalene ( DMAN), a small degree of asymmetry of the naphthalene moiety is induced by weak, asymmetric intermolecular interactions. The only manifestation of thi s asymmetry is at the level of the Laplacian of the charge distribution. Co mparing the DMAN molecule with its cation shows the consequences of protona tion, such as shortening of the C-C, and lengthening of the C(ar)-H and C-N bond lengths. These changes are even more apparent in CP properties, with rho(b) on average smaller in the cation than in the neutral molecule. Relat ionships between CP and structural parameters viz, rho(b) vs Laplacian, Lap lacian vs bond length, and rho(b) US bond length depend on bond type, and a re different for DMAN and its cation. Comparison with ab initio calculated values reveals some systematic discrepancies. Only two critical points are located between stacked DMAN molecules. Curved interaction Lines joining th ese molecules can be associated with CH...pi-electron interactions.