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(1 H )‐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(1 H )‐one, C 13 H 16 N 2 O ( 1 ), and 8a‐(4‐methylphenyl)‐2,3,4,7,8,8a‐hexahydropyrrolo[1,2‐ a ]pyrimidin‐6(1 H )‐one, C 14 H 18 N 2 O ( 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—C ar interactions. The steric volume of the substituent significantly affects the crystal packing pattern.