Crystal structures, packing features, Hirshfeld surface analyses and DFT calculations of hydrogen-bond energy of two homologous 8a-aryl-2,3,4,7,8,8a-hexahydropyrrolo[1,2-a]pyrimidin-6(1H)-ones.

The crystal structures and packing features of two homologous Meyer's bicyclic lactams with fused pyrrolidone and medium-sized perhydropyrimidine rings, namely, 8a-phenyl-2,3,4,7,8,8a-hexahydropyrrolo[1,2-a]pyrimidin-6(1H)-one, C13H16N2O (1), and 8a-(4-methylphenyl)-2,3,4,7,8,8a-hexahydropyrrolo[1,2-a]pyrimidin-6(1H)-one, C14H18N2O (2), were elucidated, and Hirshfeld surface plots were calculated and drawn for visualization and a deeper analysis of the intermolecular noncovalent interactions. Molecules of 1 and 2 are weakly linked by intermolecular C=O...H-N hydrogen bonds into chains, which are in turn weakly linked by other C=O...H-Car interactions. The steric volume of the substituent significantly affects the crystal packing pattern.

7a-Phenyl-tetra-hydro-pyrrolo-[2,1-b]oxazol-5(6H)-one.

In the title compound, C12H13NO2, the pyrrolidinone moiety is almost flat while the oxazole ring adopts an envelope conformation with the carbon atom bearing the phenyl substituent as the flap: the angle between the mean planes of the fused heterocyclic rings is 45.47 (19)°. In the crystal, C-H⋯O and C-H⋯π contacts link the mol-ecules into infinite [010] chains.