Charge density study of 2-pyridone.

The crystal structure of 2-pyridone has been redetermined from high-resolution X-ray data collected at 123 K. The molecule is in the lactam form. Bond lengths (corrected for rigid-body libration) and angles have been determined with s.u.'s of 0.001 A and 0.1 degree, respectively. The hydrogen-bonded cyclic dimers which occur in the vapor and in solution are absent in the crystal where molecules are linked by N-H...O hydrogen bonds to form puckered chains. There also appears to be a weaker C-H...O interaction (H...O, 2.57 A) and weak C-H...pi or van der Waals interactions occurring on both sides of the pyridone ring. Following a refinement of the structure assuming Stewart's rigid pseudo-atom model, the electronic charge density distribution in the crystal and its Laplacian have been calculated for atoms at rest. The total electrostatic potential has been mapped for an isolated molecule and the molecular dipole moment has been determined [8.8 (19) D; 1D approximately = 3.33564 x 10(-30) C m]. Critical points in the electron density have been located for the bonds within the molecule and for the molecular interactions cited above. For the C-H...pi interactions, only the spherical components of the valence density for the pyridone ring atoms contribute effectively at the critical points. Hence, these may be better described as van der Waals interactions.